4
Nailing the Right Exposure
When you bought your Nikon D800, you probably thought your days of worrying about getting the correct exposure were over. To paraphrase an old Kodak tagline dating back to the 19th Century—the goal is, “you press the button, and the camera does the rest.” For the most part, that’s a realistic objective. The D800 is one of the smartest cameras available when it comes to calculating the right exposure for most situations. You can generally press the mode button and spin the main command dial to switch to Program (P), Aperture-priority (A), or Shutter-priority (S) and shoot away. Even Manual (M) mode doesn’t leave you up a creek without a paddle: the D800’s analog exposure display at the bottom of the viewfinder provides feedback about how much your selected settings vary from what the D800 would have used if you’d opted for one of the semi-automated exposure modes.
But even a camera as smart as the D800 frequently can benefit from intelligent input. For example, when you shoot with the main light source behind the subject, you end up with backlighting, which can result in an overexposed background and/or an under-exposed subject. The Nikon D800 recognizes backlit situations nicely, and can properly base exposure on the main subject, producing a decent photo. Features like the D800’s built in HDR and Active D-Lighting can fine-tune exposure as you take photos, to preserve detail in the highlights and shadows.
But what if you want to underexpose the subject, to produce a silhouette effect? Or, perhaps, you might want to flip up the D800’s built-in flash unit to fill in the shadows on your subject. The more you know about how to use your D800, the more you’ll run into situations where you want to creatively tweak the exposure to provide a different look than you’d get with a straight shot.
This chapter shows you the fundamentals of exposure, so you’ll be better equipped to override the Nikon D800’s default settings when you want to, or need to. After all, correct exposure is one of the foundations of good photography, along with accurate focus and sharpness, appropriate color balance, freedom from unwanted noise and excessive contrast, as well as pleasing composition.
The Nikon D800 gives you a great deal of control over all of these, although composition is entirely up to you. You must still frame the photograph to create an interesting arrangement of subject matter, but all the other parameters are basic functions of the camera. You can let your D800 set them for you automatically, you can fine-tune how the camera applies its automatic settings, or you can make them yourself, manually. The amount of control you have over exposure, sensitivity (ISO settings), color balance, focus, and image parameters like sharpness and contrast make the D800 a versatile tool for creating images.
In the next few pages I’m going to give you a grounding in one of those foundations, and explain the basics of exposure, either as an introduction or as a refresher course, depending on your current level of expertise. When you finish this chapter, you’ll understand most of what you need to know to take well-exposed photographs creatively in a broad range of situations.
Getting a Handle on Exposure
This section explains the fundamental concepts that go into creating an exposure. If you already know about the role of f/stops, shutter speeds, and sensor sensitivity in determining an exposure, you might want to skip to the next section, which explains how the D800 calculates exposure.
In the most basic sense, exposure is all about light. Exposure can make or break your photo. Correct exposure brings out the detail in the areas you want to picture, providing the range of tones and colors you need to create the desired image. Poor exposure can cloak important details in shadow, or wash them out in glare-filled featureless expanses of white. However, getting the perfect exposure requires some intelligence—either that built into the camera or the smarts in your head—because digital sensors can’t capture all the tones we are able to see. If the range of tones in an image is extensive, embracing both inky black shadows and bright highlights, we often must settle for an exposure that renders most of those tones—but not all—in a way that best suits the photo we want to produce.
As the owner of a Nikon D800, you’re probably well aware of the traditional “exposure triangle” of aperture (quantity of light, light passed by the lens), shutter speed (the amount of time the shutter is open), and the ISO sensitivity of the sensor—all work proportionately and reciprocally to produce an exposure. The trio is itself affected by the amount of illumination that is available to work with. So, if you double the amount of light, increase the aperture by one stop, make the shutter speed twice as long, or boost the ISO setting 2X, you’ll get twice as much exposure. Similarly, you can increase any of these factors while decreasing one of the others by a similar amount to keep the same exposure.
Working with any of the three controls involves trade-offs. Larger f/stops provide less depth-of-field, while smaller f/stops increase depth-of-field (and, especially, with a camera like the D800, decreases sharpness through a phenomenon called diffraction, as discussed in Chapter 7). Shorter shutter speeds do a better job of reducing the effects of camera/subject motion, while longer shutter speeds make that motion blur more likely. Higher ISO settings increase the amount of visual noise and artifacts in your image, while lower ISO settings reduce the effects of noise. (See Figure 4.1.)
Figure 4.1 The traditional exposure triangle includes aperture, shutter speed, and ISO sensitivity.
To further understand exposure, you need to understand the six aspects of light that combine to produce an image. Start with a light source—the sun, an interior lamp, or the glow from a campfire—and trace its path to your camera, through the lens, and finally to the sensor that captures the illumination. Here’s a brief review of the things within our control that affect exposure, listed in “chronological” order (that is, as the light moves from the subject to the sensor):
Light at its source. Our eyes and our cameras—film or digital—are most sensitive to that portion of the electromagnetic spectrum we call visible light. That light has several important aspects that are relevant to photography, such as color, and harshness (which is determined primarily by the apparent size of the light source as it illuminates a subject). But, in terms of exposure, the important attribute of a light source is its intensity. We may have direct control over intensity, which might be the case with an interior light that can be brightened or dimmed. Or, we might have only indirect control over intensity, as with sunlight, which can be made to appear dimmer by introducing translucent light-absorbing or reflective materials in its path.
Light’s duration. We tend to think of most light sources as continuous. But, as you’ll learn in Chapter 8, the duration of light can change quickly enough to modify the exposure, as when the main illumination in a photograph comes from an intermittent source, such as an electronic flash.
Light reflected, transmitted, or emitted. Once light is produced by its source, either continuously or in a brief burst, we are able to see and photograph objects by the light that is reflected from our subjects toward the camera lens; transmitted (say, from translucent objects that are lit from behind); or emitted (by a candle or television screen). When more or less light reaches the lens from the subject, we need to adjust the exposure. This part of the equation is under our control to the extent we can increase the amount of light falling on or passing through the subject (by adding extra light sources or using reflectors), or by pumping up the light that’s emitted (by increasing the brightness of the glowing object).
Light passed by the lens. Not all the illumination that reaches the front of the lens makes it all the way through. Filters can remove some of the light before it enters the lens. Inside the lens barrel is a variable-sized diaphragm that produces an opening called an aperture that dilates and contracts to control the amount of light that enters the lens. You, or the D800’s autoexposure system, can control exposure by varying the size of the aperture. The relative size of the aperture is called the f/stop. (See Figure 4.2.)
Light passing through the shutter. Once light passes through the lens, the amount of time the sensor receives it is determined by the D800’s shutter, which can remain open for as long as 30 seconds (or even longer if you use the Bulb setting) or as briefly as 1/8,000th second.
Light captured by the sensor. Not all the light falling onto the sensor is captured. If the number of photons reaching a particular photosite doesn’t pass a set threshold, no information is recorded. Similarly, if too much light illuminates a pixel in the sensor, then the excess isn’t recorded or, worse, spills over to contaminate adjacent pixels. We can modify the minimum and maximum number of pixels that contribute to image detail by adjusting the ISO setting. At higher ISOs, the incoming light is amplified to boost the effective sensitivity of the sensor.
F/STOPS AND SHUTTER SPEEDS
If you’re really new to more advanced cameras (and I realize that a few ambitious amateurs do purchase the D800 as their first digital SLR), you might need to know that the lens aperture, or f/stop, is a ratio, much like a fraction, which is why f/2 is larger than f/4, just as 1/2 is larger than 1/4. However, f/2 is actually four times as large as f/4. (If you remember your high-school geometry, you’ll know that to double the area of a circle, you multiply its diameter by the square root of two: 1.4.)
Lenses are usually marked with intermediate f/stops that represent a size that’s twice as much/half as much as the previous aperture. So, a lens might be marked: f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, with each larger number representing an aperture that admits half as much light as the one before, as shown in Figure 4.2.
Shutter speeds are actual fractions (of a second), but the numerator is omitted, so that 60, 125, 250, 500, 1,000, and so forth represent 1/60th, 1/125th, 1/250th, 1/500th, and 1/1,000th second. To avoid confusion, Nikon uses quotation marks to signify longer exposures: 2”, 2”5, 4”, and so forth representing 2.0, 2.5, and 4.0-second exposures, respectively.
Figure 4.2 Top row (left to right): f/2, f/2.8, f/4, f/5.6; bottom row: f/8, f/11, f/16, f/22.
Most commonly, exposure settings are made using the aperture and shutter speed, followed by adjusting the ISO sensitivity, if it’s not possible to get the preferred exposure (that is, the one that uses the “best” f/stop or shutter speed for the depth-of-field or action stopping we want). Table 4.1 shows equivalent exposure settings using various shutter speeds and f/stops.
When the D800 is set for P mode, the metering system selects the correct exposure for you automatically, but you can change quickly to an equivalent exposure by spinning the main command dial until the desired equivalent exposure combination is displayed. You can use this Flexible Program feature more easily if you remember that you need to rotate the command dial toward the left when you want to increase the amount of depth-of-field or use a slower shutter speed; rotate to the right when you want to reduce the depth-of-field or use a faster shutter speed. The need for more/less DOF and slower/faster shutter speed are the primary reasons you’d want to use Flexible Program. This program shift mode does not work when you’re using flash.
In Aperture-priority (A) and Shutter-priority (S) modes, you can change to an equivalent exposure, but only by either adjusting the aperture (the camera chooses the shutter speed) or shutter speed (the camera selects the aperture). I’ll cover all these exposure modes later in the chapter.
Table 4.1 Equivalent Exposures
F/STOPS VERSUS STOPS
In photography parlance, f/stop always means the aperture or lens opening. However, for lack of a current commonly used word for one exposure increment, the term stop is often used. (In the past, EV served this purpose, but Exposure Value and its abbreviation have since been inextricably intertwined with its use in describing Exposure Compensation.) In this book, when I say “stop” by itself (no f/), I mean one whole unit of exposure, and am not necessarily referring to an actual f/stop or lens aperture. So, adjusting the exposure by “one stop” can mean both changing to the next shutter speed increment (say, from 1/125th second to 1/250th second) or the next aperture (such as f/4 to f/5.6). Similarly, 1/3 stop or 1/2 stop increments can mean either shutter speed or aperture changes, depending on the context. Be forewarned.
How the D800 Calculates Exposure
Although it can make some good guesses based on how the brightness levels vary within a scene, your D800 has no way of knowing for sure what it’s pointed at. So, it must make some assumptions and calculate the correct exposure based on its internal rules. One parameter is that the brightness of all—or part—of a scene will average down to a so-called middle gray tone. The conventional wisdom is that this tone is roughly 18 percent gray. Unfortunately, while the traditional 18 percent value is a middle gray in terms of what the eye sees, the D800 is actually calibrated for a slightly darker tone. This section explains how your D800 actually decides on an exposure in one of its semi-automatic (non-manual) modes.
Your D800 calculates exposure by measuring the light that passes through the lens and is bounced up by the mirror to an RGB exposure sensor with roughly 91,000 pixels, located near the focusing surface. The exposure is measured using a pattern you can select (more on that later) and based on the assumption that each area being measured reflects about the same amount of light as a neutral gray card that reflects a “middle” gray of about 12- to 18-percent reflectance. (The photographic “gray cards” you buy at a camera store have an 18-percent gray tone; your camera is calibrated to interpret a somewhat darker 12-percent gray; I’ll explain more about this later.) That “average” 12- to 18-percent gray assumption is necessary, because different subjects reflect different amounts of light. In a photo containing, say, a white cat and a dark gray cat, the white cat might reflect five times as much light as the gray cat. An exposure based on the white cat will cause the gray cat to appear to be black, while an exposure based only on the gray cat will make the white cat washed out.
This is more easily understood if you look at some photos of subjects that are dark (they reflect little light), those that have predominantly middle tones, and subjects that are highly reflective. The next few figures show a simplified scale with a middle gray 18-percent tone, plus black and white patches, along with a human figure to illustrate how different exposure measurements actually do affect an exposure.
Correctly Exposed
The image shown in Figure 4.3 represents how a photograph might appear if the exposure were calculated by measuring the light reflecting from the middle gray patch, which, for the sake of illustration, we’ll assume reflects approximately 12 to 18 percent of the light that strikes it. The exposure meter in the D800 sees an object that it thinks is a middle gray, calculates an exposure based on that, and the patch in the center of the strip is rendered at its proper tonal value. Best of all, because the resulting exposure is correct, the black patch at left and white patch at right are rendered properly as well.
When you’re shooting pictures with your D800, and the meter happens to base its exposure on a subject that averages that “ideal” middle gray, then you’ll end up with similar (accurate) results. The camera’s exposure algorithms are concocted to ensure this kind of result as often as possible, barring any unusual subjects (that is, those that are backlit, or have uneven illumination). The D800 has three different metering modes (described next), each of which is equipped to handle certain types of unusual subjects, as I’ll outline.
Overexposed
Figure 4.4 shows what would happen if the exposure were calculated based on metering the leftmost, black patch. The light meter sees less light reflecting from the black square than it would see from a gray middle-tone subject, and so figures, “Aha! I need to add exposure to brighten this subject up to a middle gray!” That lightens the “black” patch, so it now appears to be gray.
But now the patch in the middle that was originally middle gray is overexposed and becomes light gray. And the white square at right is now seriously overexposed and loses detail in the highlights, which have become a featureless white. Our human subject is similarly overexposed.
Figure 4.3 When exposure is calculated based on the middle-gray tone in the center of the card, the black and white patches are rendered accurately, too, and our model is properly exposed.
Figure 4.4 When exposure is calculated based on the black square at lower left, the black patch looks gray, the gray patch appears to be a light gray, and the white square is seriously overexposed.
Figure 4.5 When exposure is calculated based on the white patch on the right, the other two patches, and the photo, are underexposed.
Underexposed
The third possibility in this simplified scenario is that the light meter might measure the illumination bouncing off the white patch, and try to render that tone as a middle gray. A lot of light is reflected by the white square, so the exposure is reduced, bringing that patch closer to a middle gray tone. The patches that were originally gray and black are now rendered too dark. Clearly, measuring the gray card—or a substitute that reflects about the same amount of light, is the only way to ensure that the exposure is precisely correct. (See Figure 4.5.)
As you can see, the ideal way to measure exposure is to meter from a subject that reflects 12 to 18 percent of the light that reaches it. If you want the most precise exposure calculations, the solution is to use a stand-in, such as the evenly illuminated gray card I mentioned earlier. The standard Kodak gray card reflects 18 percent of the light that reaches it, what is considered to be a middle gray. But, as I said earlier, your D800 is calibrated for a somewhat darker tone than that middle gray, roughly 12 percent gray, so you would need to add about one-half stop more exposure than the value metered from the card.
Another substitute for a gray card is the palm of a human hand (the backside of the hand is too variable). But a human palm, regardless of ethnic group, is even brighter than a standard gray card, so instead of one-half stop more exposure, you need to add one additional stop. That is, if your meter reading is 1/500th of a second at f/11, use 1/500th second at f/8 or 1/250th second at f/11 instead. (Both exposures are equivalent.)
If you actually wanted to use a gray card, place it in your frame near your main subject, facing the camera, and with the exact same even illumination falling on it that is falling on your subject. Then, use the Spot metering function (described in the next section) to calculate exposure. Of course, in most situations, it’s not necessary to do this. Your camera’s light meter will do a good job of calculating the right exposure, especially if you use the exposure tips in the next section. But, I felt that explaining exactly what is going on during exposure calculation would help you understand how your D800’s metering system works.
EXTERNAL METERS CAN BE CALIBRATED
The light meters built into your D800 are calibrated at the factory and can only be changed using the Fine Tune Optimal Exposure option (Custom Setting b6). But if you use a hand-held incident or reflective light meter, you can calibrate it, using the instructions supplied with your meter. Because a hand-held meter can be calibrated to the 18-percent gray standard (or any other value you choose), my rant about the myth of the 18-percent gray card doesn’t apply.
Why are so many photographers under the impression that camera light meters are calibrated to the 18-percent “standard,” rather than the true value, which may be 12 to 14 percent, depending on the vendor? You’ll find this misinformation in an alarming number of places. I’ve seen the 18-percent “myth” taught in camera classes; I’ve found it in books, and even been given this wrong information from the technical staff of camera vendors. (They should know better—the same vendors’ engineers who design and calibrate the cameras have the right figure.)
The most common explanation is that during a revision of Kodak’s instructions for its gray cards in the 1970s, the advice to open up an extra half stop was omitted, and a whole generation of shooters grew up thinking that a measurement off a gray card could be used as-is. The proviso returned to the instructions by 1987, it’s said, but by then it was too late. Next to me is a (c)2006 version of the instructions for KODAK Gray Cards, Publication R-27Q, and the current directions read (with a bit of paraphrasing from me in italics):
For subjects of normal reflectance increase the indicated exposure by 1/2 stop.
For light subjects use the indicated exposure; for very light subjects, decrease the exposure by 1/2 stop. (That is, you’re measuring a cat that’s lighter than middle gray.)
If the subject is dark to very dark, increase the indicated exposure by 1 to 1-1/2 stops. (You’re shooting a black cat.)
MODES, MODES, AND MORE MODES
Call them modes or methods, the Nikon D800 seems to have a lot of different sets of options that are described using similar terms. Here’s how to sort them out:
Metering method. These modes determine the parts of the image within the 91,000-segment sensor array that are examined in order to calculate exposure. The D800 may look at many different points within the image, segregating them by zone (Matrix metering), examine the same number of points, but give greater weight to those located in the middle of the frame (Center-weighted metering), or evaluate only a limited number of points in a limited area (Spot metering).
Exposure method. These modes determine which settings are used to expose the image. The D800 may adjust the shutter speed, the aperture, or both, or even ISO setting (if Auto ISO is active), depending on the method you choose.
To meter properly you’ll want to choose both the metering method (how light is evaluated) and exposure method (how the appropriate shutter speeds and apertures are chosen). I’ll describe both in the following sections.
Choosing a Metering Method
The D800 has three different schemes for evaluating the light received by its exposure sensors: Matrix (with several variations, depending on what lens you have attached), Center-weighted, and Spot metering. Select the mode you want to use by rotating the metering switch located concentrically with the AE-L/AF-L button on the back of the camera to the right of the viewfinder. You’ll be able to see which metering method is selected by noting the symbols shown in the top control panel LCD.
INSTANT SWITCHING
If you frequently use one metering method, but occasionally like to switch to another method on the fly, you can redefine the D800’s Fn, Preview, or AE-L/AF-L buttons to shift to your alternate mode instantly. The Fn button can be programmed to provide Matrix metering, Center-weighted metering, or Spot metering (as well as other functions discussed in Chapter 12), using Custom Setting entry CSM #f4. The Preview button can be assigned that role with CSM #f5, while the same option is available for the AE-L/AF-L button in CSM #f6.
The really cool thing is that you can define one button for, say, Center-weighted metering, another one for Spot metering, and then set the main Metering mode switch to Matrix, and thus be able to switch among all three on a whim. I’ve done this as a way to compare the exposure settings of the three metering methods while composing a single image in the viewfinder. I’ve also found the capability useful when I’m, say, working with Matrix metering and want to zero in on a particular area of the frame temporarily using Spot metering. The indicators in the viewfinder will help you remember what metering mode you’ve switched to.
Here is what you need to know about each metering method:
Matrix Metering
For its various Matrix metering modes, the D800 slices up the frame into 91,000 different zones in an RGB (red/green/blue) array that covers most of the sensor area, shown in Figure 4.6. When Matrix metering is active, an icon appears in the monochrome status LCD (enlarged in the upper-left corner of the figure; in the viewfinder it’s actually located at lower left). In all cases, the D800 evaluates the differences between the zones, and compares them with a built-in database of 30,000 actual images to make an educated guess about what kind of picture you’re taking. For example, if the top sections of a picture are much lighter than the bottom portions, the algorithm can assume that the scene is a landscape photo with lots of sky. An image that includes most of the lighter portions in the center area may be a portrait. A typical image suitable for Matrix metering is shown in Figure 4.7.
The Nikon D800 also uses information other than brightness to make its evaluation:
3D Color Matrix metering III. This metering mode is used by default when the D800 is equipped with a lens that has a type G or type D designator in its name, such as the 24-120mm f/4G ED VR AF-S Nikkor lens. The G after the f/4 is the giveaway. (More on lens nomenclature in Chapter 7.) The camera calculates exposure based on brightness, colors of the subject matter (that is, blue pixels in the upper part of the image are probably sky; green pixels in the lower half probably foliage), focus point, and distance information. The D800 is able to use that additional distance data to better calculate what kind of scene you have framed. For example, if you’re shooting a portrait with a longer focal-length lens focused to about 5 to 12 feet from the camera, and the upper half of the scene is very bright, the camera assumes you would prefer to meter for the rest of the image, and discount the bright area. However, if the camera has a wide-angle lens attached and is focused at infinity, the D800 can assume you’re taking a landscape photo and take the bright upper area into account to produce better-looking sky and clouds.
Color Matrix metering III. If you have a non-G or non-D lens equipped with a CPU chip (these are generally older lenses, although chips can sometimes be added to optics that lack them), the distance range is not used. Instead, only focus, brightness, and color information is taken into account to calculate an appropriate exposure.
Figure 4.6 Matrix metering calculates exposure based on 91,000 points in the frame.
Figure 4.7 Complex scenes lend themselves to the exposure interpretation provided by Matrix metering.
Color Matrix metering. If you’re using a non-CPU lens (such as an older manual focus lens) and have specified the focal length and maximum aperture in the Setup menu (as described in Chapter 10), then the D800 uses plain old color Matrix metering, which evaluates exposure based only on brightness and color information detected in the scene.
With other lenses. If you don’t specify focal length or maximum aperture for a non-CPU lens, the D800 defaults to Center-weighted metering.
Matrix metering is best for most general subjects, because it is able to intelligently analyze a scene and make an excellent guess of what kind of subject you’re shooting a great deal of the time. The camera can tell the difference between low-contrast and high-contrast subjects by looking at the range of differences in brightness across the scene. Because the D800 has a fairly good idea about what kind of subject matter you are shooting, it can underexpose slightly when appropriate to preserve highlight detail when image contrast is high. (It’s often possible to pull detail out of shadows that are too dark using an image editor, but once highlights are converted to white pixels, they are gone forever.)
CAUTION
If you’re using a strong filter, including a polarizing filter, split-color filter, or neutral-density filter (particularly a graduated neutral-density filter), you should switch from Matrix metering to Center-weighted, because the filter can affect the relationships between the different areas of the frame used to calculate a Matrix exposure. For example, a polarizing filter produces a sky that is darker than usual, hindering the Matrix algorithm’s recognition of a landscape photo. Extra dark or colored filters disturb the color relationships used for color Matrix metering, too.
Center-Weighted Metering
In this mode, the exposure meter emphasizes a zone in the center of the frame to calculate exposure, as shown in Figure 4.8. I must apologize for the psychedelic color scheme, but color-coding was the easiest way to see the center-weighted coverage at the four optional spot sizes offered by the D800. About 75 percent of the exposure is based on that central area, and the remaining 25 percent of the exposure is based on the rest of the frame. The center-weighted area can take up as little as 5.8 percent or as much as 36 percent of the entire frame area. Your options are:
8mm circle. This smaller circle size, represented by the orange disc in Figure 4.8, covers 5.8% of the image frame. Use this size if the center area you want to emphasize is relatively small, but not small enough to switch to Spot metering (which has a 4mm metering circle). The distinction is a subtle one, and your choice of this size center-weighted circle will probably come from experience with the kinds of subjects you shoot. I find it useful for shooting plays with multiple performers, when Spot metering may be too narrow and you don’t want to bother manipulating the position of the spot metering zone.
12mm circle. The default value for the center-weighted metering circle is 12mm, which extends out to the edges of the yellow area of the illustration, roughly 13 percent of the image area. If you’re using a non-CPU lens, then this 12mm value is applied even if you’ve specified an 8mm, 15mm, or 20mm circle. It’s a good all-around choice for most subjects that lend themselves to center weighting, like the one shown in Figure 4.9.
15mm circle. This slightly larger circle covers about 20 percent of the frame area, extending out to the blue edges in the illustration. It is a good choice with larger subjects that are in bright or dark surroundings that might confuse Matrix metering.
20mm circle. The largest center-weighted circle covers 36 percent of the frame area, out to the magenta edges of the disc in the figure. I use this when my subject occupies a large area in the viewfinder, but would like to ignore some distracting bright or dark spots at the edges or corners.
Averaging. This setting isn’t a center weighting at all, but, instead, averages the illumination of the entire frame to calculate exposure. It’s a good choice for evenly lit subjects, without any remarkably bright or dark areas, or when you simply want a decent exposure under varied lighting conditions.
Figure 4.8 Center-weighted metering calculates exposure based on the full frame, but gives 75 percent of the weight to the center area using the circle size you select; the remaining 25 percent of the exposure is determined by the rest of the image area.
Figure 4.9 Scenes with the main subject in the center, surrounded by areas that are significantly darker or lighter, are perfect for Center-weighted metering.
The theory with all center-weighted metering is that, for most pictures, the main subject will be located in the center. So, if the D800 reads the center portion and determines that the exposure for that region should be f/8 at 1/250th second, while the outer area, which is a bit darker, calls for f/4 at 1/125th second, the camera will give the center portion the most weight and arrive at a final exposure of f/5.6 at 1/250th second.
Center-weighting in general works best for portraits, architectural photos, backlit subjects with extra-bright backgrounds (such as snow or sand), and other pictures in which the most important subject is located in the middle of the frame. As the name suggests, the light reading is weighted toward the central portion, but information is also used from the rest of the frame. If your main subject is surrounded by very bright or very dark areas, the exposure might not be exactly right. However, this scheme works well in many situations if you don’t want to use one of the other modes. This mode can be useful for close-ups of subjects like flowers, or for portraits. You can adjust the size of the center area assigned the greatest weight using CSM #b5, as described in Chapter 12. As I noted above, the available circles include 8mm, 12mm, 15mm, 20mm, and “Average” (which in effect, covers the entire screen to produce what is called Average metering).
Spot Metering
Spot metering is favored by those of us who have used a hand-held light meter to measure exposure at various points (such as metering highlights and shadows separately). However, you can use Spot metering in any situation where you want to individually measure the light reflecting from light, midtone, or dark areas of your subject—or any combination of areas.
This mode confines the reading to a limited 4mm area in the viewfinder, making up only 1.5 percent of the image, as shown in Figure 4.10. The circle is centered on the current focus point (which can be any of the 39 focus points, not just the center one shown in Figure 4.10), but is larger than the focus point, so don’t fall into the trap of believing that exposure is being measured only within the brackets that represent the active focus point. This is the only metering method you can use to tell the D800 exactly where to measure exposure when using the optical viewfinder. However, if a non-CPU lens is mounted, or you have selected Auto-area AF, only the center focus point is used to spot meter.
You’ll find Spot metering useful when you want to base exposure on a small area in the frame. If that area is in the center of the frame, so much the better. If not, you’ll have to make your meter reading for an off-center subject using an appropriate focus point, and then lock exposure by pressing the shutter release halfway, or by pressing the AE-L/AF-L button. This mode is best for subjects where the background is significantly brighter or darker, as in Figure 4.11.
Figure 4.10 Spot metering calculates exposure based on a center spot that’s only 1.5 percent of the image area, centered around the current focus point.
Figure 4.11 Spot metering allowed measuring exposure from the two performers.
Using Spot Metering
Matrix and Center-weighted metering basically have few options to worry about. As I noted earlier, when using Center-weighted, you can vary the size of the center spot from 8mm up to 20mm, or select Averaging, and both Matrix and Center-weighted metering are affected by exposure compensation changes and CSM #b6 Fine-Tune Optimal Exposure adjustments. Spot metering, on the other hand, can benefit from your input in selecting the spot used. Here are some considerations to keep in mind:
Moving the spot. Remember that you don’t move the metering spot itself; the D800 uses the current focus spot. So, you must be using an AF area mode that allows changing the AF spot, which happens to be any of the AF area modes except Auto-area AF.
Choosing a compatible AF-area mode. Press the button in the center of the focus mode switch on the front of the camera (just below the lens release button), and rotate the main command dial to switch to AF-C mode, then rotate the sub-command dial to cycle among Single-point, 9-point Dynamic-area, 21-point Dynamic-area, 51-point Dynamic-area, or 3D-tracking (but not Auto). Use AF-S mode instead, and you can switch only between Auto and Single-point. All these AF-area modes except for Auto-area AF will allow you to switch the AF point to any of the 11 or 51 focus points in the viewfinder.
Available points. The Single, 9, 21, and 51 numbers refer only to the total number of points centered around the selected point that will be used to determine focus, not the number of zones you can use to locate the focus point. That’s determined by CSM #a7, where you can select either AF11 or AF51. If you’ve selected AF11, then your focus point selection is limited to 11 more widely spread AF points, and the metering spot is confined to those same points. I’ll explain AF area modes in more detail in Chapter 5; it’s necessary to drag the feature into this chapter only because the spot metering zone is dependent on where the AF point is located.
Wrap around. You’ll use the multi selector’s directional buttons to move the AF point around within the focus brackets in the viewfinder—and the metering spot with it. The focus point’s movement will stop at the left/right/top/bottom edges unless you’ve turned on focus point wrap-around in CSM #a6.
When using Auto-area AF. If you’ve selected Auto-area AF, the center focus point will always be used—even if the camera selects a different point for the autofocus function. That’s actually a positive: since in Auto-area AF mode you don’t know what the focus spot will be until you press the shutter release halfway, it’s good to know that the D800 will be using the center spot. While Spot metering is most useful when not using Auto-area AF, it still functions, albeit in a less flexible way.
Choosing an Exposure Method
You’ll find four methods for choosing the appropriate shutter speed and aperture, when using the semi-automatic/manual modes. (Scene modes, which use their own exposure biases, are described next.) You can choose among Program, Aperture-priority, Shutter-priority, or Manual options by pressing the mode button at top right of the camera, and rotating the main dial until the mode of your choice appears on the top control panel or in the viewfinder. Your decision on which is best for a given shooting situation will depend on things like your need for lots of (or less) depth-of-field, a desire to freeze action or allow motion blur, or how much noise you find acceptable in an image. Each of the D800’s exposure methods emphasizes one aspect of image capture or another. This section introduces you to all four.
Aperture-Priority
In A mode, you specify the lens opening used, and the D800 selects the shutter speed. Aperture-priority is especially good when you want to use a particular lens opening to achieve a desired effect. Perhaps you’d like to use the smallest f/stop possible to maximize depth-of-field in a close-up picture. Or, you might want to work with a large f/stop to throw everything except your main subject out of focus, as in Figure 4.12. Maybe you’d just like to “lock in” a particular f/stop because it’s the sharpest available aperture with that lens. Or, you might prefer to use, say, f/2.8 on a lens with a maximum aperture of f/1.4, because you want the best compromise between speed and sharpness.
Figure 4.12 Use Aperture-priority to “lock in” a large f/stop when you want to blur the background.
Aperture-priority can even be used to specify a range of shutter speeds you want to use under varying lighting conditions, which seems almost contradictory. But think about it. You’re shooting a soccer game outdoors with a telephoto lens and want a relatively high shutter speed, but you don’t care if the speed changes a little should the sun duck behind a cloud. Set your D800 to A, and adjust the aperture until a shutter speed of, say, 1/1,000th second is selected at your current ISO setting. (In bright sunlight at ISO 400, that aperture is likely to be around f/11.) Then, go ahead and shoot, knowing that your D800 will maintain that f/11 aperture (for sufficient depth-of-field as the soccer players move about the field), but will drop down to 1/750th or 1/500th second if necessary should the lighting change a little.
When the shutter speed indicator in the viewfinder and the top-panel monochrome LCD blink, that indicates that the D800 is unable to select an appropriate shutter speed at the selected aperture and that over- and underexposure will occur at the current ISO setting. That’s the major pitfall of using A: you might select an f/stop that is too small or too large to allow an optimal exposure with the available shutter speeds. For example, if you choose f/2.8 as your aperture and the illumination is quite bright (say, at the beach or in snow), even your camera’s fastest shutter speed might not be able to cut down the amount of light reaching the sensor to provide the right exposure. Or, if you select f/8 in a dimly lit room, you might find yourself shooting with a very slow shutter speed that can cause blurring from subject movement or camera shake. Aperture-priority is best used by those with a bit of experience in choosing settings. Many seasoned photographers leave their D800 set on A all the time. The exposure indicator scale in the status panel and viewfinder indicate the amount of under- or overexposure.
When to use Aperture-priority:
General landscape photography. The D800 is a great camera for landscape photography, of course, because its high resolution allows making huge, gorgeous prints, as well as smaller prints that are filled with eye-popping detail. Aperture priority is a good tool for ensuring that your landscape is sharp from foreground to infinity, if you select an f/stop that provides maximum depth-of-field (without running into the D800’s diffraction bug-a-boo, which I’ll discuss in Appendix B).
If you use A mode and select an aperture like f/11 or f/16, it’s your responsibility to make sure the shutter speed selected is fast enough to avoid losing detail to camera shake, or that the D800 is mounted on a tripod. One thing that new landscape photographers fail to account for is the movement of distant leaves and tree branches. When seeking the ultimate in sharpness, go ahead and use Aperture-priority, but boost ISO sensitivity a bit, if necessary, to provide a sufficiently fast shutter speed, whether shooting hand-held or with a tripod.
Specific landscape situations. Aperture-priority is also useful when you have no objection to using a long shutter speed, or, particularly, want the D800 to select one. Waterfalls are a perfect example. You can use A mode, set your camera to ISO 100, use a small f/stop, and let the camera select a longer shutter speed that will allow the water to blur as it flows. Indeed, you might need to use a neutral density to get a sufficiently long shutter speed. But Aperture-priority mode is a good start.
Portrait photography. Portraits are the most common applications of selective focus. A medium-large aperture (say, f/5.6 or f/8) with a longer lens/zoom setting (in the 85mm-135mm range) will allow the background behind your portrait subject to blur. A very large aperture (I frequently shoot wide open with my 85mm f/1.4D AF Nikkor) lets you apply selective focus to your subject’s face. With a three-quarters view of your subject, as long as her eyes are sharp, it’s okay if the far ear or her hair is out of focus, as in Figure 4.13.
Figure 4.13 A large aperture is useful for portrait photography as long as the eyes are sharp.
When you want to ensure optimal sharpness. All lenses have an aperture or two at which they perform best, providing the level of sharpness you expect from a camera with the resolution of the D800. That’s usually about two stops down from wide open, and thus will vary depending on the maximum aperture of the lens. My 85mm f/1.4 is good wide open, but it’s even sharper at f/2.8 or f/4; I shoot my 70-200mm f/2.8 wide open at concerts, but, if I can use f/4 instead, I’ll get better results. A relatively slow lens like my favorite travel lens—the super-compact Nikon 28-200mm f/3.5-5.6G ED IF zoom—really needs to be set at f/11 if I crank it out to its maximum focal length. Aperture-priority allows me to use each lens at its very best f/stop.
Close-up/Macro photography. Depth-of-field is typically very shallow when shooting macro photos, and you’ll want to choose your f/stop carefully. Perhaps you need the smallest aperture you can get away with to maximize depth-of-field. Or, you might want to use a wider stop to emphasize your subject, as I did with the photo of the miniature trains in Figure 4.14. A mode comes in very useful when shooting close-up pictures. Because macro work is frequently done with the D800 mounted on a tripod, and your close-up subjects, if not living creatures, may not be moving much, a longer shutter speed isn’t a problem. Aperture-priority can be your preferred choice.
Figure 4.14 Extra depth-offield came in handy when shooting closeups of these miniature trains.
Shutter-Priority
Shutter-priority (S) is the inverse of Aperture-priority: you choose the shutter speed you’d like to use, and the camera’s metering system selects the appropriate f/stop. Perhaps you’re shooting action photos and you want to use the absolute fastest shutter speed available with your camera; in other cases, you might want to use a slow shutter speed to add some blur to a sports photo that would be mundane if the action were completely frozen. (See the ends of the hockey sticks in Figure 4.15.) Shutter-priority mode gives you some control over how much action-freezing capability your digital camera brings to bear in a particular situation.
You’ll also encounter the same problem as with Aperture-priority when you select a shutter speed that’s too long or too short for correct exposure under some conditions. As in A mode, it’s possible to choose an inappropriate shutter speed. If that’s the case, the shutter speed indicator in the viewfinder and control panel LCD will blink.
When to use Shutter-priority:
To reduce blur from subject motion. Set the shutter speed of the D800 to a higher value to reduce the amount of blur from subjects that are moving. The exact speed will vary depending on how fast your subject is moving and how much blur is acceptable. You might want to freeze a basketball player in mid-dunk with a 1/1000th second shutter speed, or use 1/250th second to allow the spinning wheels of a motocross racer to blur a tiny bit to add the feeling of motion.
Figure 4.15 Lock the shutter at a specific speed to introduce blur into an action shot.
To add blur from subject motion. There are times when you want a subject to blur, say, when shooting waterfalls with the camera set for a one- or two-second exposure in Shutter-priority mode.
To add blur from camera motion when you are moving. Say you’re panning to follow a pair of relay runners. You might want to use Shutter-priority mode and set the D800 for 1/60th second, so that the background will blur as you pan with the runners. The shutter speed will be fast enough to provide a sharp image of the athletes, as shown in Figure 4.16.
To reduce blur from camera motion when you are moving. In other situations, the camera may be in motion, say, because you’re shooting from a moving train or auto, and you want to minimize the amount of blur caused by the motion of the camera. Shutter-priority is a good choice here, too.
Landscape photography hand-held. If you can’t use a tripod for your landscape shots, you’ll still probably want the sharpest image possible. Shutter-priority can allow you to specify a shutter speed that’s fast enough to reduce or eliminate the effects of camera shake. Just make sure that your ISO setting is high enough that the D800 will select an aperture with sufficient depth-of-field, too.
Concerts, stage performances. I shoot a lot of concerts with my 70-200mm f/2.8 VR Nikkor lens, and have discovered that, when vibration reduction is taken into account, a shutter speed of 1/180th second is fast enough to eliminate camera shake that can result from hand-holding the D800 with this lens, and also to avoid blur from the movement of all but the most energetic performers. I use Shutter-priority and set the ISO so the camera will select an aperture in the f/4-5.6 range.
Figure 4.16 Shutter-priority allows you to specify a speed that will render a moving subject sharp as you pan.
Program Mode
Program mode (P) uses the D800’s built-in smarts to select the correct f/stop and shutter speed using a database of picture information that tells it which combination of shutter speed and aperture will work best for a particular photo. If the correct exposure cannot be achieved at the current ISO setting, the shutter speed and aperture will blink in the viewfinder and control panel. You can then boost or reduce the ISO to increase or decrease sensitivity.
The D800’s recommended exposure can be overridden if you want. Use the EV (exposure value) setting feature (described later, because it also applies to S and A modes) to add or subtract exposure from the metered value. And, as I mentioned earlier in this chapter, in Program mode you can rotate the main command dial to change from the recommended setting to an equivalent setting (as shown previously in Table 4.1) that produces the same exposure, but using a different combination of f/stop and shutter speed.
This is called “Flexible Program” by Nikon. Rotate the main command dial left to reduce the size of the aperture (going from, say, f/4 to f/5.6), so that the D800 will automatically use a slower shutter speed (going from, say, 1/250th second to 1/125th second). Rotate the main command dial right to use a larger f/stop, while automatically producing a shorter shutter speed that provides the same equivalent exposure as metered in P mode. An asterisk appears next to the P in the control panel so you’ll know you’ve overridden the D800’s default program setting. Your adjustment remains in force until you rotate the main command dial until the asterisk disappears, or you switch to a different exposure mode, or turn the D800 off.
MAKING EV CHANGES
Sometimes you’ll want more or less exposure than indicated by the D800’s metering system. Perhaps you want to underexpose to create a silhouette effect, or overexpose to produce a high key look. It’s easy to use the D800’s exposure compensation system to override the exposure recommendations. Press the EV button on the top of the camera (just southeast of the shutter release). Then rotate the main command dial left to add exposure, and right to subtract exposure. The EV change you’ve made remains for the exposures that follow, until you manually zero out the EV setting. The EV plus/minus icon appears in the viewfinder and control panel to warn you that an exposure compensation change has been entered. You can increase or decrease exposure over a range of plus or minus five stops. (If you’ve activated Easy Exposure Compensation using CSM #b4, as described in Chapter 12, you don’t have to hold down the EV button; rotating the main or sub-command dials alone changes the EV value when using Program, Aperture-priority, Shutter-priority, or Manual exposure modes.)
When to use Program mode priority:
When you’re in a hurry to get a grab shot. The D800 will do a pretty good job of calculating an appropriate exposure for you, without any input from you.
When you hand your camera to a novice. Set the D800 to P, hand the camera to your friend, relative, or trustworthy stranger you meet in front of the Eiffel Tower, point to the shutter release button and viewfinder, and say, “Look through here, and press this button.”
When no special shutter speed or aperture settings are needed. If your subject doesn’t require special anti- or pro-blur techniques, and depth-of-field or selective focus aren’t important, use P as a general-purpose setting. You can still make adjustments to increase/decrease depth-of-field or add/reduce motion blur with a minimum of fuss.
Manual Exposure
Part of being an experienced photographer comes from knowing when to rely on your D800’s automation (with P mode), when to go semi-automatic (with S or A), and when to set exposure manually (using M). Some photographers actually prefer to set their exposure manually, as the D800 will be happy to provide an indication of when its metering system judges your manual settings provide the proper exposure, using the analog exposure scale at the bottom of the viewfinder.
Manual exposure can come in handy in some situations. You might be taking a silhouette photo and find that none of the exposure modes or EV correction features give you exactly the effect you want. Set the exposure manually to use the exact shutter speed and f/stop you need. Or, you might be working in a studio environment using multiple flash units. The additional flash are triggered by slave devices (gadgets that set off the flash when they sense the light from another flash unit, or, perhaps from a radio or infrared remote control). Your camera’s exposure meter doesn’t compensate for the extra illumination, so you need to set the aperture manually.
Because, depending on your proclivities, you might not need to set exposure manually very often, you should still make sure you understand how it works. Fortunately, the D800 makes setting exposure manually very easy. Just press the mode button and rotate the main command dial to change to Manual mode, and then turn the main command dial to set the shutter speed, and the sub-command dial to adjust the aperture. Press the shutter release halfway or press the AE lock button, and the exposure scale in the viewfinder shows you how far your chosen setting diverges from the metered exposure.
Older lenses that lack the CPU chip that tells the Nikon D800 what kind of lens is mounted can be used with Aperture-priority and Manual exposure modes only, assuming you’ve entered the Non-CPU Lens information in the Setup menu, as described in Chapter 7. If the D800 knows the maximum aperture of the lens, you can set the aperture using the lens’s aperture ring, and, in A mode, the camera will automatically select an appropriate shutter speed. In Manual mode, you can set the aperture, and the analog exposure scale in the viewfinder will indicate when you’ve set the correct shutter speed manually. If a non-CPU lens is mounted and you try to set Program or Shutter-priority modes, the D800 switches to Aperture-priority automatically. The process works because the D800 camera body and other advanced Nikon models (from the old D200 on up through the D4) have a mechanical linkage built into the lens mount that tells the camera when the f/stop has been changed. Less advanced Nikon digital cameras, including the D5100 and D3200, lack this linkage and cannot meter with non-CPU lenses.
When to use Manual exposure:
When working in the studio. If you’re working in a studio environment, you generally have total control over the lighting and can set exposure exactly as you want. The last thing you need is for the D800 to interpret the scene and make adjustments of its own. Use M and shutter speed, aperture, and (as long as you don’t use ISO-Auto) the ISO setting are totally up to you.
When using non-dedicated flash. The Nikon Creative Lighting System (CLS) is cool, and can even be used to coordinate use of your D800’s internal flash with external compatible dedicated flash units, like the SB-910. But if you’re working with non-CLS flash units, particularly studio flash plugged into the D800’s PC/X connector, the camera has no clue about the intensity of the flash, so you’ll have to dial in the appropriate aperture manually.
If you’re using a hand-held light meter. Determining that appropriate aperture, both for flash exposures and shots taken under continuous lighting, can be determined by a hand-held light meter, flash meter, or combo meter that measures both kinds of illumination. With an external meter, you can measure highlights, shadows, backgrounds, or additional subjects separately, and use Manual exposure to make your settings.
When you want to outsmart the metering system. Your D800’s metering system is “trained” to react to unusual lighting situations, such as backlighting, extra bright illumination, or low-key images with murky shadows. In many cases, it can counter these “problems” and produce a well-exposed image. But what if you don’t want a well-exposed image? Manual exposure allows you to produce silhouettes in backlit situations, wash out all the middle tones to produce a luminous look, or underexpose to create a moody or ominous dark-toned photograph.
Adjusting Exposure with ISO Settings
Another way of adjusting exposures is by changing the ISO sensitivity setting. Sometimes photographers forget about this option, because the common practice is to set the ISO once for a particular shooting session (say, at ISO 200 for bright sunlight outdoors, or ISO 800 when shooting indoors) and then forget about ISO. ISOs higher than ISO 200 or 400 are seen as “bad” or “necessary evils.” However, changing the ISO is a valid way of adjusting exposure settings, particularly with the Nikon D800, which produces good results at ISO settings that create grainy, unusable pictures with some other camera models.
Indeed, I find myself using ISO adjustment as a convenient alternate way of adding or subtracting EV when shooting in Manual mode, and as a quick way of choosing equivalent exposures when in Program or Shutter-priority or Aperture-priority modes. For example, I’ve selected a Manual exposure with both f/stop and shutter speed suitable for my image using, say, ISO 200. I can change the exposure in 1/3 stop increments by holding down the ISO button located on the left side of the camera next to the LCD, and spinning the main command dial one click at a time. The difference in image quality/noise at ISO 200 is negligible if I dial in ISO 160 or ISO 125 to reduce exposure a little, or change to ISO 250 or 320 to increase exposure. I keep my preferred f/stop and shutter speed, but still adjust the exposure.
Or, perhaps, I am using S mode and the metered exposure at ISO 200 is 1/500th second at f/11. If I decide on the spur of the moment I’d rather use 1/500th second at f/8, I can press the ISO button and spin the main command dial three clicks left to switch to ISO 100. Of course, it’s a good idea to monitor your ISO changes, so you don’t end up at ISO 6400 accidentally. An ISO indicator appears in the control panel and in the viewfinder to remind you what sensitivity setting has been dialed in.
ISO settings can, of course, also be used to boost or reduce sensitivity in particular shooting situations. The D800 can use ISO settings from ISO 100 up to ISO 6400, plus L 1.0 and L 2.0 (ISO 80/ISO 50 equivalent), and H 1.0 and H 2.0 (ISO 12800 and 25600 equivalent). The camera can also adjust the ISO automatically as appropriate for various lighting conditions. When you choose the Auto ISO setting in the Shooting menu, as described in Chapter 8, the D800 adjusts the sensitivity dynamically to suit the subject matter, based on minimum shutter speed and ISO limits you have prescribed. As I note in Chapter 11, you should use Auto ISO cautiously if you don’t want the D800 to use an ISO higher than you might otherwise have selected.
Dealing with Noise
Visual image noise is that random grainy effect that some like to use as a special effect, but which, most of the time, is objectionable because it robs your image of detail even as it adds that “interesting” texture. Noise is caused by two different phenomena: high ISO settings and long exposures.
High ISO noise commonly appears when you raise your camera’s sensitivity setting above ISO 400. With the Nikon D800, noise may become visible at ISO 1600, and is often fairly noticeable at ISO 3200. At ISO 6400 and above, noise is usually quite bothersome. Nikon tips you off that ISO 12800 and 25600 may be tools used in special circumstances only by labeling them H1.0 and H2.0. You can expect noise and increase in contrast in any pictures taken at these lofty ratings. (You can also expect some higher contrast when using the low-end L 1.0 and L 2.0 settings.) High ISO noise appears as a result of the amplification needed to increase the sensitivity of the sensor. While higher ISOs do pull details out of dark areas, they also amplify non-signal information randomly, creating noise. You’ll find a High ISO NR choice in the Shooting menu, where you can specify High, Norm, or Low noise reduction, or turn the feature off entirely. Because noise reduction tends to soften the grainy look while robbing an image of detail, you may want to disable the feature if you’re willing to accept a little noise in exchange for more details.
A similar noisy phenomenon occurs during long time exposures, which allow more photons to reach the sensor, increasing your ability to capture a picture under low light conditions. However, the longer exposures also increase the likelihood that some pixels will register random phantom photons, often because the longer an imager is “hot,” the warmer it gets, and that heat can be mistaken for photons. There’s also a special kind of noise that CMOS sensors like the one used in the D800 are potentially susceptible to. With a CCD, the entire signal is conveyed off the chip and funneled through a single amplifier and analog-to-digital conversion circuit. Any noise introduced there is, at least, consistent. CMOS imagers, on the other hand, contain millions of individual amplifiers and A/D converters, all working in unison. Because these circuits don’t necessarily all process in precisely the same way all the time, they can introduce something called fixed-pattern noise into the image data.
Fortunately, Nikon’s electronics geniuses have done an exceptional job minimizing noise from all causes in the D800. Even so, you might still want to apply the optional long exposure noise reduction that can be activated using Long Exp. NR in the Shooting menu, where the feature can be turned On or Off. This type of noise reduction involves the D800 taking a second, blank exposure, and comparing the random pixels in that image with the photograph you just took. Pixels that coincide in the two represent noise and can safely be suppressed. This noise reduction system, called dark frame subtraction, effectively doubles the amount of time required to take a picture, and is used only for exposures longer than one second. Noise reduction can reduce the amount of detail in your picture, as some image information may be removed along with the noise. So, you might want to use this feature with moderation.
You can also apply noise reduction to a lesser extent using Photoshop, and when converting RAW files to some other format, using your favorite RAW converter, or an industrial-strength product like Noise Ninja (www.picturecode.com) to wipe out noise after you’ve already taken the picture.
Bracketing
Bracketing is a method for shooting several consecutive exposures using different settings, as a way of improving the odds that one will be exactly right. Alternatively, bracketing can be used to create a series of photos with slightly different exposures (or white balances) in anticipation that one of the exposures will be “better” from a creative standpoint. For example, bracketing can supply you with a normal exposure of a backlit subject, one that’s “underexposed,” producing a silhouette effect, and a third that’s “overexposed” to create still another look.
Before digital cameras took over the universe, it was common to bracket exposures, shooting, say, a series of three photos at 1/125th second, but varying the f/stop from f/8 to f/11 to f/16. In practice, smaller than whole-stop increments were used for greater precision, and lenses with apertures that were set manually commonly had half-stop detents on their aperture rings, or could easily be set to a mid-way position between whole f/stops. It was just as common to keep the same aperture and vary the shutter speed, although in the days before electronic shutters, film cameras often had only whole increment shutter speeds available.
Today, cameras like the D800 can bracket exposures much more precisely, and bracket white balance and Active D-Lighting (described later in this chapter) as well. While WB bracketing is sometimes used when getting color absolutely correct in the camera is important, autoexposure bracketing is used much more often. When this feature is activated, the D800 takes a series of consecutive photos: starting with the metered “correct” exposure, then progressing to shots with less exposure, and additional shots with more exposure, using an increment of your choice up to +1/−1 stops. (Choose between increments by setting Custom Setting b2.) In A mode, the shutter speed will change, while in S mode, the aperture will change as the bracketed exposures are made.
ACTIVATING BRACKETING
Once you’ve set up the type of bracketing you want to use, as described next, taking a bracketed set of exposures is easy. When bracketing is active, to initiate exposing a set just press the Bracketing Burst button. (By default the Fn button, but you can also define the Preview and AE-L/AF-L buttons to perform this function. Use CSM #e5, #e6, and #e7 to define the Bracketing Burst button.) Once the burst button is pressed, all shots in the set will be taken each time you press the shutter release button once.
Setting up autoexposure bracketing parameters is trickier than it needs to be, but you can follow these steps to get results like those shown in Figure 4.17:
1. Choose type of bracketing. First, select the type of bracketing you want to do, using Custom Setting e5 (Auto Bracketing Set), as explained in Chapter 12. You can select autoexposure and flash, autoexposure only, flash only, white balance only, and ADL bracketing.
If you plan on shooting in Manual exposure mode, you can specify how bracketing is performed using Custom Setting e6. Your choices there are flash+shutter speed, flash+shutter speed+aperture, flash+aperture, or flash only. White balance and ADL bracketing are not available in Manual exposure mode.
2. Choose bracketing order. With CSM #e7 you can select MTR > Under > Over or Under > MTR > Over bracket orders. I prefer the latter order, as it makes certain types of manual HDR exposures easier. You can, for example, shoot 9 bracketed exposures, each 1 stop different from the last, and then delete the even-numbered shots to end up with five bracketed images that are two stops apart. It’s easier to drop the correct exposures if you use the Under > MTR > Over bracket order.
3. Press bracketing setting button. Press and hold the BKT button on the top-left side of the D800.
4. Select number of bracketed exposures. With the BKT setting button held down, rotate the main command dial to choose the number of shots in the sequence, 0 (which turns bracketing off), 2, 3, 5, 7, or 9 bracketed shots. Rotate the main command dial counterclockwise to center the bracketed shots around the metered exposure (the 2 value is not available if you do this), and rotate it clockwise to choose 2 or 3 bracketed exposures concentrated either over or under the metered exposure. This is the most confusing aspect of bracketing, so I’ll explain how this works in more detail next.
Figure 4.17 Bracketing can give you three different exposures of the same subject.
5. Choose bracket increment. With the setting button still held down, rotate the sub-command dial to choose the exposure increment: 1/3, 2/3, or 1 EV (unless you’ve redefined the exposure compensation increment to 1/2 or 1EV in Custom Setting b2).
6. Frame and shoot. As you take your photos, the camera will vary exposure, flash level, or white balance for each image, based on the bracketing “program” you selected, and in the order you specified in Custom Setting e7. In Single-frame mode, you’ll need to press the shutter release button the number of times you specified for the exposures in your bracketed burst (2, 3, 5, 7, or 9 shots). I’ve found it easy to forget that I am shooting bracketed pictures, stop taking my sequence, and then wonder why the remaining pictures in my defined burst are “incorrectly” exposed. To avoid that, I often set the D800 to one of the two continuous shooting modes, so that all my bracketed pictures are taken at once. The D800 does provide indicators on the monochrome LCD (a BKT indicator as well as a bracketing progress indicator), but they may be overlooked.
7. Turn bracketing off. When you’re finished bracketing shots, remember to press the bracket setting button and rotate the main command dial until the number of shots in the sequence is 0F, and the BKT indicator is no longer displayed.
More on Bracketing
Unless you have previous experience with Nikon’s bracketing procedures, the process can seem a little confusing, particularly when it comes time to select the number of bracketed exposures. That’s because Nikon combines two functions in one setting: how many actual shots in the burst and where those shots are placed within the overall scheme of exposure. Both those parameters are set when you hold down the BKT button and spin the main command dial. That’s an entirely different operation than setting the exposure increment, which, as I said, is accomplished by holding down the BKT setting button and spinning the sub-command dial.
Here’s what happens. When you go to set the number of bracketed exposures, there are two “modes” based on which direction you rotate the main command dial:
Rotate main command dial counterclockwise. The number of exposures increases from 0 to 3, 5, 7, or 9 images. In all cases, the bracketed exposure values will be evenly spaced on either side of the metered exposure, using the increment you have selected separately (with the sub-command dial). Suppose you have already chosen 1/3 EV as your increment, and then rotate the main command dial counterclockwise. At the 3F 0.3 position, the exposures will be taken at the metered exposure, plus 1/3 stop less and 1/3 stop more (three shots in all). At the 5F 0.3 position, the exposures will be taken at the metered exposure, plus 1/3 stop and 2/3 stop less, as well as 1/3 stop and 2/3 stop more (five shots in all). The bracketed exposures are evenly spread on either side of the metered exposure.
Rotate the main command dial clockwise. In that case, the first setting that appears on the control panel is -2F 0.3, which will tell the D800 to shoot one picture at the measured exposure, and one at 1/3 stop less (two shots). The next click produces a readout of +2F 0.3, which produces one shot at the metered exposure, and one at 1/3 stop more. You can also select -3F 0.3 or +3F 0.3. In all cases, the additional bracketed shots are biased either toward under- or overexposure. That’s as far as the clockwise spin to the right will take you. There are no -5F or +5F or larger numeric settings available.
A lot of people find this concept confusing, because the Nikon manual discusses these variations (which it calls “bracketing programs”) in the section that follows the description of exposure increments, which are set with the sub-command dial. Yes, the exposure increment you select does affect the “program,” but the number of shots and distribution of the bracketed exposures is an entirely different concept, and is controlled only by spinning the main command dial.
White Balance Bracketing
When you choose white balance bracketing, the D800 does not take multiple exposures. It takes one exposure and saves a series of JPEG images using different color balances. That makes sense, if you think about it. The camera always starts off with a RAW exposure first, no matter whether the camera is set to JPEG, RAW, or RAW+JPEG. If you’ve selected JPEG-only mode, the camera converts the initial RAW exposure to JPEG format using the settings you’ve opted for in the camera, and then discards the RAW data. In RAW mode, the camera stores the RAW data as an NEF file, and also creates a Basic JPEG version of the image that is embedded in the RAW file as a thumbnail. That thumbnail is what you’re actually looking at on the back-panel LCD when you review your pictures; you never actually see the RAW file itself until you import it into your image editor. Your computer may also use the embedded JPEG file, when it displays a RAW image. Finally, if you save in RAW+JPEG, you end up with two files: the NEF RAW file (with its embedded JPEG image) and a separate JPEG file at the quality level you specify (Fine, Normal, or Basic).
Since the RAW file that the camera initially captures contains all the digital information captured during exposure, when you specify white balance bracketing, the D800 needs to take only one picture—and then save a JPEG file at each of the required white balance settings. One snap, and you get two to nine JPEG files at the quality level you specified, bracketed as you directed. Very slick. As you might guess, WB bracketing is applied only to JPEG files; you can’t specify WB bracketing if you’ve chosen RAW or RAW+JPEG. RAW files created are always unmodified, and will be converted according to the white balance settings you opted for in the camera when the photo is imported into your image editor (if you make no white balance changes during importation).
White balance bracketing produces JPEG files that vary, not by f/stops (which is the case with exposure bracketing), but by units called mireds (micro reciprocal degrees) that are used to specify color temperature. You don’t really need to understand mireds at all, other than to know that WB bracketing varies the color temperature of your images by 5, 10, or 15 mireds when you select increments of 1, 2, or 3, respectively. Changes are made only in the amber-blue range; bracketing isn’t applied to the green-magenta color bias.
As with exposure bracketing, hold down the bracket button and spin the main command dial to select the WB program (for example, off, two shots/amber bias, two shots/blue bias, three shots, amber/+blue bias, and the sub-command dial to choose the increment). The whole process can be a little non-intuitive, so Table 4.2 might be a help.
ADL Bracketing
Active D-Lighting is a feature that improves the rendition of detail in highlights and shadows when you’re photographing high contrast scenes. If you’re taking photos in a contrasty environment, Active D-Lighting can automatically improve the apparent dynamic range of your image as you shoot, without additional effort on your part. When shooting non-bracketed ADL images, or bracketed ADL sets you can specify five different ADL “intensities”: Auto, Extra High, High, Normal, or Low. You can read more about how Active D-Lighting works in Chapter 11.
To initiate Active D-Lighting bracketing, select it from the CSM #e5 Auto Bracketing Set menu entry. It’s the last entry in the list. Thereafter, press and hold the BKT button you’ve specified, and follow these steps:
1. Choose number of shots in sequence. While holding the BKT button, rotate the main command dial and choose 0 (Off), 2, 3, 4, or 5 shots. At any setting other than 0, an ADL-BKT symbol will appear in the top-panel monochrome display, and BKT will be shown in the D800’s viewfinder.
Two shots. One shot with ADL off and another at the selected value will be taken.
Three shots. One shot with ADL off, and one shot with Low and one with Normal Active D-Lighting will be taken.
Four shots. One shot with ADL off, and one each with Low, Normal, and High Active D-Lighting will be taken.
Five shots. One shot with ADL off, and one each at the Low, Normal, High, and Extra High settings will be captured.
2. Choose value for a two-shot ADL set. Selecting 3, 4, or 5 shots in the set uses several different ADL intensities automatically. If you select 2, one shot will have ADL turned off, and you can specify the intensity for the second shot by rotating the sub-command dial. You’ll see A, L, N, H, or H+ (for Auto, Low, Normal, High, and Extra High) displayed on the monochrome status LCD.
3. Take your shots. Press the shutter release to produce an ADL-bracketed set. If the D800 is set to CL or CH the entire bracketed sequence will be taken, and then the camera will stop. Press the shutter release again to take another bracketed set. Note that ADL bracketing is “sticky”; if you switch the camera off before the sequence is complete, the set will resume the next time the D800 is turned on.
4. Cancel bracketing. Press the BKT button and rotate the main command dial until 0 is displayed as the number of shots in the sequence.
Table 4.2 White Balance Bracketing Programs
Working with HDR
High dynamic range (HDR) photography is quite the rage these days, and entire books have been written on the subject. It’s not really a new technique—film photographers have been combining multiple exposures for ages to produce a single image of, say, an interior room while maintaining detail in the scene visible through the windows.
It’s the same deal in the digital age. Suppose you wanted to photograph a dimly lit room that had a bright window showing an outdoors scene. Proper exposure for the room might be on the order of 1/60th second at f/2.8 at ISO 200, while the outdoors scene probably would require f/11 at 1/400th second. That’s almost a 7 EV step difference (approximately 7 f/stops) and well beyond the dynamic range of any digital camera, including the Nikon D800.
Until camera sensors gain much higher dynamic ranges (which may not be as far into the distant future as we think), special tricks like Active D-Lighting and HDR photography will remain basic tools. With the Nikon D800, you can create in-camera HDR exposures, or shoot HDR the old-fashioned way—with separate bracketed exposures that are later combined in a tool like Photomatix or Adobe’s Merge to HDR image-editing feature. I’m going to show you how to use both.
Auto HDR
The D800’s in-camera HDR feature is simple, not particularly flexible, but still surprisingly effective in creating high dynamic range images. It’s also remarkably easy to use. Although it combines only two images to create a single HDR photograph, in some ways it’s as good as the manual HDR method I’ll describe in the section after this one. For example, it allows you to specify an exposure differential of three stops/EV between the two shots, whereas the D800 shooting bracketed exposures is limited to one EV between shots. (I’ll show you how to overcome that limitation easily.)
Figure 4.18 illustrates how the two shots that the D800’s HDR feature merges might look. There is a three-stop differential between the underexposed image at left, and the overexposed image at right. The in-camera HDR processing is able to combine the two to derive an image similar to the one shown in Figure 4.19, which has a much fuller range of tones.
To use the D800’s HDR feature, just follow these steps. The feature does not work if you have selected RAW or RAW+JPEG formats, or have one of the bracketing features turned on.
1. Activate the menu. Press the MENU button and navigate to the Shooting menu, represented by a camera icon. (If you need more help using the D800’s menu system, you’ll find an introduction at the beginning of Chapter 11.)
2. Scroll down to HDR. Press the right multi selector button. The screen shown in Figure 4.20 appears.
3. Turn on HDR. Choose HDR Mode, press right, and select either On (series) if you want to shoot multiple HDR photos consecutively, or On (single photo) to take a single HDR image and then shut the feature off. Press OK to confirm.
4. Set increment. Choose Exposure Differential, press the right button, and select Auto (the D800 chooses the differential based on how contrasty it deems your scene to be), or 1EV, 2EV, or 3EV. Auto is a good choice for your initial experiments. Or, select a higher EV value for higher contrast subjects, and a lower value for lower contrast subjects. Press OK to confirm.
Figure 4.18 The underexposed image (left) can be combined with the overexposed version (right)…
Figure 4.19 …to produce this merged high dynamic range (HDR) image.
Figure 4.20 Choose HDR parameters.
TIP
You can reassign the BKT button to serve as an HDR activate control using CSM #f8. That will save you a trip to the main menu. Press the BKT button and rotate the main command dial to select HDR Mode and the sub-command dial to select the Exposure Differential. Smoothing remains as it was last set.
5. Choose smoothing. The edges of the areas in your image may have a high contrast, poster-edge like effect in some circumstances. Smoothing adjusts the shading between these edges. You can select High, Normal, or Low. You may need to experiment until you see exactly what kind of results you get with various types of images. Press OK to confirm.
6. Take your shot. Although you can shoot HDR hand-held, you’ll get the best results with the D800 mounted on a tripod, and with subjects that don’t display a lot of motion. (That is, waterfalls are a poor choice.) While the D800 is combining your two shots, the message Job will appear on the monochrome status LCD, and Job Hdr will be shown at the bottom of the viewfinder.
Bracketing and Merge to HDR
If your credo is “If you want something done right, do it yourself,” you can also shoot HDR manually, without resorting to the D800’s HDR mode. Instead, you can shoot individual images either by manually bracketing or using the D800’s auto bracketing modes, described earlier in this chapter.
While my goal in this book is to show you how to take great photos in the camera rather than how to fix your errors in Photoshop, the Merge to HDR Pro feature in Adobe’s flagship image editor is too cool to ignore. The ability to have a bracketed set of exposures that are identical except for exposure is key to getting good results with this Photoshop feature, which allows you to produce images with a full, rich dynamic range that includes a level of detail in the highlights and shadows that is almost impossible to achieve with digital cameras.
When you’re using Merge to HDR Pro, you’d take several pictures, some exposed for the shadows, some for the middle tones, and some for the highlights. The exact number of images to combine is up to you. Four to seven is a good number. Then, you’d use the Merge to HDR Pro command to combine all of the images into one HDR image that integrates the well-exposed sections of each version. Here’s how.
The images should be as identical as possible, except for exposure. So, it’s a good idea to mount the D800 on a tripod, use a remote release like MC-30, and take all the exposures in one burst. Just follow these steps:
1. Set up the camera. Mount the D800 on a tripod.
2. Set the camera to shoot a bracketed burst with an increment of 1EV. The description of how to do this will be found earlier in this chapter. As I noted there, you can set the D800 to shoot up to 9 exposures, each one stop/EV apart, and use all 9 for your HDR merger. Or, you can go ahead and shoot 9 and discard the even numbered shots to arrive at five images spaced two EV apart.
3. Choose an f/stop. Set the camera for Aperture-priority and select an aperture that will provide a correct exposure at your initial settings for the series of manually bracketed shots. And then leave this adjustment alone! You don’t want the aperture to change for your series, as that would change the depth-of-field. You want the D800 to adjust exposure only using the shutter speed.
4. Choose manual focus. You don’t want the focus to change between shots, so set the D800 to manual focus, and carefully focus your shot.
5. Choose RAW exposures. Set the camera to take RAW files, which will give you the widest range of tones in your images.
6. Take your bracketed set. Press the button on the remote (or carefully press the shutter release or use the self-timer) and take the set of bracketed exposures.
7. Continue with the Merge to HDR Pro steps listed next. You can also use a different program, such as Photomatix, if you know how to use it.
DETERMINING THE BEST EXPOSURE DIFFERENTIAL
How do you choose the number of EV/stops to separate your exposures? You can use histograms, described at the end of this chapter, to determine the correct bracketing range. Take a test shot and examine the histogram. Reduce the exposure until dark tones are clipped off at the left of the resulting histogram. Then, increase the exposure until the lighter tones are clipped off at the right of the histogram. The number of stops between the two is the range that should be covered using your bracketed exposures.
The next steps show you how to combine the separate exposures into one merged high dynamic range image. The sample images in Figure 4.21 show the results you can get from a four-shot bracketed sequence.
1. Copy your images to your computer. If you use an application to transfer the files to your computer, make sure it does not make any adjustments to brightness, contrast, or exposure. You want the real raw information for Merge to HDR Pro to work with.
2. Activate Merge to HDR Pro. Choose File > Automate > Merge to HDR Pro.
3. Select the photos to be merged. Use the Browse feature to locate and select your photos to be merged. You’ll note a checkbox that can be used to automatically align the images if they were not taken with the camera mounted on a rock-steady support. This will adjust for any slight movement of the camera that might have occurred when you changed exposure settings.
4. Choose parameters (optional). The first time you use Merge to HDR Pro, you can let the program work with its default parameters. Once you’ve played with the feature a few times, you can read the Adobe help files and learn more about the options than I can present in this non-software-oriented camera guide. (See Figure 4.22.)
5. Click OK. The merger begins.
6. Save. Once HDR merge has done its thing, save the file to your computer.
Figure 4.21 Four bracketed photos should look like this.
Figure 4.22 Use the Merge to HDR Pro command in Photoshop or Photoshop Elements to combine the four images.
Adobe Photoshop
If you do everything correctly, you’ll end up with a photo like the one shown in Figure 4.23.
What if you don’t have the opportunity, inclination, or skills to create several images at different exposures, as described? If you shoot in RAW format, you can still use Merge to HDR, working with a single original image file. What you do is import the image into Photoshop several times, using Adobe Camera Raw to create multiple copies of the file at different exposure levels.
For example, you’d create one copy that’s too dark, so the shadows lose detail, but the highlights are preserved. Create another copy with the shadows intact and allow the highlights to wash out. Then, you can use Merge to HDR to combine the two and end up with a finished image that has the extended dynamic range you’re looking for. (This concludes the image-editing portion of the chapter. We now return you to our alternate sponsor: photography.)
Figure 4.23 You’ll end up with an extended dynamic range photo like this one.
Fixing Exposures with Histograms
While you can often recover poorly exposed photos in your image editor, your best bet is to arrive at the correct exposure in the camera, minimizing the tweaks that you have to make in post-processing. However, you can’t always judge exposure just by viewing the image on your D800’s LCD after the shot is made. Nor can you get a 100 percent accurately exposed picture by using the D800’s live view feature. Ambient light may make the LCD difficult to see, and the brightness level you’ve set can affect the appearance of the playback image.
Instead, you can use a histogram, which is a chart displayed on the D800’s LCD that shows the number of tones that have been captured at each brightness level. You must use the information to provide correction for the next shot you take, because no “live” histogram is available. In Playback mode, the D800 offers four histogram variations in two screens: one histogram that shows overall brightness levels for an image (Figure 4.24, left) and an alternate version that also shows brightness, but offers additional histograms that separates the red, green, and blue channels of your image into separate graphs (Figure 4.24, right).
DISPLAYING HISTOGRAMS
To view all the available histograms on your screen, you must have the D800 set up properly. First, you’ll need to mark RGB Histograms and Overview using the Playback Display Options entry in the Playback menu, as described in Chapter 11. (Don’t forget to select Done and press OK when finished specifying.) That will make the two screens that show Histograms visible when you cycle among the informational screens while pressing the multi selector up/down buttons while an image is displayed.
Figure 4.24 Four histograms are available on two different screens during playback.
The most basic histogram is displayed during playback when you press the multi selector up/down buttons to produce the Overview Data screen, as described briefly in Chapter 2. This screen provides a small histogram at the right side that displays the distribution of luminance or brightness. The most useful histogram screen is the RGB Histogram, which displays both a luminance chart and separate red, green, and blue charts.
Tonal Range
Histograms help you adjust the tonal range of an image, the span of dark to light tones, from a complete absence of brightness (black) to the brightest possible tone (white), and all the middle tones in between. Because all values for tones fall into a continuous spectrum between black and white, it’s easiest to think of a photo’s tonality in terms of a black-and-white or grayscale image, even though you’re capturing tones in three separate color layers of red, green, and blue.
Because your images are digital, the tonal “spectrum” isn’t really continuous: it’s divided into discrete steps that represent the different tones that can be captured. Figure 4.25 may help you understand this concept. The gray steps shown range from 100 percent gray (black) at the left, to 0 percent gray (white) at the right, with 20 gray steps in all (plus white).
Along the bottom of the chart are the digital values from 0 to 255 recorded by your sensor for an image with 8 bits per channel. (8 bits of red, 8 bits of green, and 8 bits of blue equal a 24 bit, full-color image.) Any black captured would be represented by a value of 0, the brightest white by 255, and the midtones would be clustered around the 128 marker. The actual scale may be “finer” and record say, 0 to 4094 for an image captured when the D800 is set to 12 bits per channel in the NEF (RAW) Bit Depth setting of the Shooting menu (see Chapter 11 for more detail on that option).
Figure 4.25 A tonal range from black (left) to white (right) and all the gray values in between.
Grayscale images (which we call black-and-white photos) are easy to understand. Or, at least, that’s what we think. When we look at a black-and-white image, we think we’re seeing a continuous range of tones from black to white, and all the grays in between. But, that’s not exactly true. The blackest black in any photo isn’t a true black, because some light is always reflected from the surface of the print, and if viewed on a screen, the deepest black is only as dark as the least-reflective area a computer monitor can produce. The whitest white isn’t a true white, either, because even the lightest areas of a print absorb some light (only a mirror reflects close to all the light that strikes it), and, when viewing on a computer monitor, the whites are limited by the brightness of the display’s LCD or LED picture elements. Lacking darker blacks and brighter, whiter whites, that continuous set of tones doesn’t cover the full grayscale tonal range.
The full scale of tones becomes useful when you have an image that has large expanses of shades that change gradually from one level to the next, such as areas of sky, water, or walls. Think of a picture taken of a group of campers around a campfire. Since the light from the fire is striking them directly in the face, there aren’t many shadows on the campers’ faces. All the tones that make up the features of the people around the fire are compressed into one end of the brightness spectrum—the lighter end.
Yet, there’s more to this scene than faces. Behind the campers are trees, rocks, and perhaps a few animals that have emerged from the shadows to see what is going on. These are illuminated by the softer light that bounces off the surrounding surfaces. If your eyes become accustomed to the reduced illumination, you’ll find that there is a wealth of detail in these shadow images.
This campfire scene would be a nightmare to reproduce faithfully under any circumstances. If you are an experienced photographer, you are probably already wincing at what is called a high-contrast lighting situation. Some photos may be high in contrast when there are fewer tones and they are all bunched up at limited points in the scale. In a low-contrast image, there are more tones, but they are spread out so widely that the image looks flat. Your digital camera can show you the relationship between these tones using a histogram.
Histogram Basics
Your D800’s histograms are a simplified display of the numbers of pixels at each of 256 brightness levels, producing an interesting mountain range effect. Although separate charts may be provided for brightness and the red, green, and blue channels, when you first start using histograms, you’ll want to concentrate on the brightness histogram.
Each vertical line in the graph represents the number of pixels in the image for each brightness value, from 0 (black) on the left to 255 (white) on the right. The vertical axis measures that number of pixels at each level.
Although histograms are most often used to fine-tune exposure, you can glean other information from them, such as the relative contrast of the image. Figure 4.26 shows the upper half of the Overview screen, with an image having normal contrast. In such an image, most of the pixels are spread across the image, with a healthy distribution of tones throughout the midtone section of the graph. That large peak at the right side of the graph represents all those light tones in the sky. A normal-contrast image you shoot may have less sky area, and less of a peak at the right side, but notice that very few pixels hug the right edge of the histogram, indicating that the lightest tones are not being clipped because they are off the chart.
Figure 4.26 This image has fairly normal contrast, even though there is a peak of light tones at the right side representing the sky.
With a lower-contrast image, like the one shown in Figure 4.27, the basic shape of the previous histogram will remain recognizable, but gradually will be compressed together to cover a smaller area of the gray spectrum. The squished shape of the histogram is caused by all the grays in the original image being represented by a limited number of gray tones in a smaller range of the scale.
Figure 4.27 This low-contrast image has all the tones squished into one section of the grayscale.
Instead of the darkest tones of the image reaching into the black end of the spectrum and the whitest tones extending to the lightest end, the blackest areas of the scene are now represented by a light gray, and the whites by a somewhat lighter gray. The overall contrast of the image is reduced. Because all the darker tones are actually a middle gray or lighter, the scene in this version of the photo appears lighter as well.
Going in the other direction, increasing the contrast of an image produces a histogram like the one shown in Figure 4.28. In this case, the tonal range is now spread over the entire width of the chart, but, except for the bright sky, there is not much variation in the middle tones; the mountain “peaks” are not very high. When you stretch the gray-scale in both directions like this, the darkest tones become darker (that may not be possible) and the lightest tones become lighter (ditto). In fact, shades that might have been gray before can change to black or white as they are moved toward either end of the scale.
Figure 4.28 A high-contrast image produces a histogram in which the tones are spread out.
The effect of increasing contrast may be to move some tones off either end of the scale altogether, while spreading the remaining grays over a smaller number of locations on the spectrum. That’s exactly the case in the example shown. The number of possible tones is smaller and the image appears harsher.
Understanding Histograms
The important thing to remember when working with the histogram display in your D800 is that changing the exposure does not change the contrast of an image. The curves illustrated in the previous three examples remain exactly the same shape when you increase or decrease exposure. I repeat: The proportional distribution of grays shown in the histogram doesn’t change when exposure changes; it is neither stretched nor compressed. However, the tones as a whole are moved toward one end of the scale or the other, depending on whether you’re increasing or decreasing exposure. You’ll be able to see that in some illustrations that follow.
So, as you reduce exposure, tones gradually move to the black end (and off the scale), while the reverse is true when you increase exposure. The contrast within the image is changed only to the extent that some of the tones can no longer be represented when they are moved off the scale.
To change the contrast of an image, you must do one of four things:
Change the D800’s contrast setting using the menu system. You’ll find these adjustments in your camera’s Picture Controls menus, as explained in Chapter 11.
Use your camera’s shadow-tone “booster.” As previously discussed, Active D-Lighting (or plain old D-Lighting) applied after the fact from the Retouch menu (Chapter 13) can also adjust contrast.
Alter the contrast of the scene itself, for example by using a fill light or reflectors to add illumination to shadows that are too dark.
Attempt to adjust contrast in post-processing using your image editor or RAW file converter. You may use features such as Levels or Curves (in Photoshop, Photoshop Elements, and many other image editors), or work with HDR software to cherry-pick the best values in shadows and highlights from multiple images.
Of the four of these, the third—changing the contrast of the scene—is the most desirable, because attempting to fix contrast by fiddling with the tonal values is unlikely to be a perfect remedy. However, adding a little contrast can be successful because you can discard some tones to make the image more contrasty. However, the opposite is much more difficult. An overly contrasty image rarely can be fixed, because you can’t add information that isn’t there in the first place.
What you can do is adjust the exposure so that the tones that are already present in the scene are captured correctly. Figure 4.29 shows the histogram for an image that is badly underexposed. You can guess from the shape of the histogram that many of the dark tones to the left of the graph have been clipped off. There’s plenty of room on the right side for additional pixels to reside without having them become overexposed. So, you can increase the exposure (either by changing the f/stop or shutter speed, or by adding an EV value) to produce the corrected histogram shown in Figure 4.30.
Figure 4.29 A histogram of an underex-posed image may look like this.
Conversely, if your histogram looks like the one shown in Figure 4.31, with bright tones pushed off the right edge of the chart, you have an overexposed image, and you can correct it by reducing exposure. In addition to the histogram, the D800 has its Highlights option, which, when activated, shows areas that are overexposed with flashing tones (often called “blinkies”) in the review screen. Depending on the importance of this “clipped” detail, you can adjust exposure or leave it alone. For example, if all the dark-coded areas in the review are in a background that you care little about, you can forget about them and not change the exposure, but if such areas appear in facial details of your subject, you may want to make some adjustments.
Figure 4.30 Adding exposure will produce a histogram like this one.
Figure 4.31 A histogram of an overexposed image will show clipping at the right side.
By default, the Highlights display shows “blinkies” for the luminance channel, but you can separately view highlights for the red, green, and blue channels. Just follow these steps:
1. With an image displayed, and the highlights/histogram screen shown, hold down the Zoom In button.
2. Press the multi selector left/right buttons to cycle among RGB (all channels), R, G, and B.
3. When a channel is framed in an orange outline, the highlight information for that channel is shown in the thumbnail image in the upper-left corner. At the bottom left of the screen RGB, R, G, or B will be highlighted to show the currently active channel.
In working with histograms, your goal should be to have all the tones in an image spread out between the edges, with none clipped off at the left and right sides. Underexposing (to preserve highlights) should be done only as a last resort, because retrieving the underexposed shadows in your image editor will frequently increase the noise, even if you’re working with RAW files. A better course of action is to expose for the highlights, but, when the subject matter makes it practical, fill in the shadows with additional light, using reflectors, fill flash, or other techniques rather than allowing them to be seriously underexposed.
The more you work with histograms, the more useful they become. One of the first things that histogram veterans notice is that it’s possible to overexpose one channel even if the overall exposure appears to be correct. For example, flower photographers soon discover that it’s really, really difficult to get a good picture of a red rose, like the one shown in Figure 4.32. The exposure looks okay—but there’s no detail in the rose’s petals. Looking at the histogram (see Figure 4.33) shows why: the red channel is blown out. If you look at the red histogram, there’s a peak at the right edge that indicates that highlight information has been lost. In fact, the green channel has been blown, too, and so the green parts of the flower also lack detail. Only the blue channel’s histogram is entirely contained within the boundaries of the chart, and, on first glance, the white luminance histogram at top of the column of graphs seems fairly normal.
Any of the primary channels—red, green, or blue—can blow out all by themselves, although bright reds seem to be the most common problem area. More difficult to diagnose are overexposed tones in one of the “in-between” hues on the color wheel. Overexposed yellows (which are very common) will be shown by blowouts in both the red and green channels. Too-bright cyans will manifest as excessive blue and green highlights, while overexposure in the red and blue channels reduces detail in magenta colors. As you gain experience, you’ll be able to see exactly how anomalies in the RGB channels translate into poor highlights and murky shadows.
Figure 4.32 It’s common to lose detail in bright red flowers because the red channel becomes over exposed even when the other channels are properly exposed.
Figure 4.33 The RGB histograms show that both the red and green channels are overexposed.
The only way to correct for color channel blowouts is to reduce exposure. As I mentioned earlier, you might want to consider filling in the shadows with additional light to keep them from becoming too dark when you decrease exposure. In practice, you’ll want to monitor the red channel most closely, followed by the blue channel, and slightly decrease exposure to see if that helps. Because of the way our eyes perceive color, we are more sensitive to variations in green, so green channel blowouts are less of a problem, unless your main subject is heavily colored in that hue. If you plan on photographing a frog hopping around on your front lawn, you’ll want to be extra careful to preserve detail in the green channel, using bracketing or other exposure techniques outlined in this chapter.