Aperture affects depth of field

The aperture setting, or f-stop, affects depth of field, which refers to how far in front of and behind your point of focus — which, presumably, is your subject — appears acceptably sharp. With a shallow depth of field, your subject appears more sharply focused than background and foreground objects; with a long depth of field, the sharp-focus zone spreads over a greater distance.

When you reduce the aperture size — “stop down the aperture,” in photo lingo — by choosing a higher f-stop number, you increase depth of field. As an example, see Figure 4-3. For both shots, I established focus on the fountain statue. Notice that the background in the first image, taken at f/13, is sharper than in the right example, taken at f/5.6. Aperture is just one contributor to depth of field, however; the focal length of the lens and the distance between that lens and your subject also affect how much of the scene stays in focus. See Chapter 5 for the complete story on depth of field.

One way to remember the relationship between f-stop and depth of field is to think of the f as focus: The higher the f-stop number, the larger the zone of sharp focus. (Please don’t share this tip with photography elites, who will roll their eyes and inform you that the f in f-stop most certainly does not stand for focus but, rather, for the ratio between aperture size and lens focal length — as if that’s helpful to know if you aren’t an optical engineer. Chapter 1 explains focal length, which is helpful to know.)

Shutter speed affects motion blur

At a slow shutter speed, moving objects appear blurry, whereas a fast shutter speed captures motion cleanly. This phenomenon has nothing to do with the actual focus point of the camera but rather on the movement occurring — and being recorded by the camera — while the shutter is open.

Compare the photos in Figure 4-3, for example. The static elements are perfectly focused in both images, although the background in the left photo appears sharper because that image was shot using a higher f-stop, increasing depth of field. But how the camera rendered the moving portion of the scene — the fountain water — was determined by shutter speed. At 1/25 second (left photo), the water blurs, giving it a misty look. At 1/125 second (right photo), the droplets appear more sharply focused, almost frozen in mid-air. How fast a shutter speed you need to freeze action depends on the speed of your subject.

If your picture suffers from overall image blur, like the picture shown in Figure 4-4, where even stationary objects appear out of focus, the camera moved during the exposure — which is always a danger when you handhold the camera at slow shutter speeds. The longer the exposure time, the longer you have to hold the camera still to avoid the blur caused by camera shake.

Freezing action isn’t the only way to use shutter speed to creative effect. When shooting waterfalls, for example, many photographers use a slow shutter speed to give the water even more of a blurry, romantic look than you see in the fountain example. With colorful moving subjects, a slow shutter can produce some cool abstract effects and create a heightened sense of motion. Chapter 7 offers examples of both effects.

ISO affects image noise

As ISO increases, making the image sensor more reactive to light, you increase the risk of noise. Noise looks like sprinkles of sand and is similar in appearance to film grain, a defect that often mars pictures taken with high ISO film. Figure 4-5 offers an example.

Ideally, then, you should always use the lowest ISO setting on your camera to ensure top image quality. But sometimes the lighting conditions don’t permit you to do so. Take the rose photos in Figure 4-6 as an example. When I shot these pictures, I didn’t have a tripod, so I needed a shutter speed fast enough to allow a sharp handheld image.

I opened the aperture to f/6.3, which was the widest setting on the lens I was using, to allow as much light as possible into the camera. At ISO 100, the camera needed a shutter speed of 1/40 second to expose the picture, and that shutter speed wasn’t fast enough for a successful handheld shot. You see the blurred result on the left in Figure 4-6. Raising the ISO to 200 allowed a shutter speed of 1/80 second, which was fast enough to capture the flower cleanly, as shown on the right in the figure.

Fortunately, you don’t encounter serious noise on the T6/1300D until you really crank up the ISO. In fact, you may even be able to get away with a fairly high ISO if you keep your print or display size small. Some people probably wouldn’t even notice the noise in the left image in Figure 4-5 unless they were looking for it, for example. But as with other image defects, noise becomes more apparent as you enlarge the photo, as shown on the right in that same figure. Noise is also easier to spot in shadow areas of your picture and in large areas of solid color.

How much noise is acceptable (and, therefore, how high an ISO is safe) is a personal choice. Even a little noise isn’t acceptable for pictures that require the highest quality, such as images for a product catalog or a travel shot that you want to blow up to poster size.

It’s also important to know that a high ISO isn’t the only cause of noise: A long exposure time (slow shutter speed) can also produce the defect. Combining a high ISO with a long exposure time, then, increases noise risk.

Doing the exposure balancing act

Aperture, shutter speed, and ISO combine to determine image brightness. So changing any one setting means that one or both of the others must also shift to maintain the same image brightness.

Suppose that you’re shooting a soccer game and you notice that although the overall exposure looks great, the players appear slightly blurry at the current shutter speed. If you raise the shutter speed, you have to compensate with either a larger aperture, to allow in more light during the shorter exposure, or a higher ISO setting, to make the camera more sensitive to the light. Which way should you go? Well, it depends on whether you prefer the reduced depth of field that comes with a larger aperture or the increased risk of noise that accompanies a higher ISO. Of course, you can also adjust both settings to get the exposure results you need. (I explain how to actually adjust all these settings later.)

All photographers have their own approaches to finding the right combination of aperture, shutter speed, and ISO, and you’ll no doubt develop your own system when you become more practiced at using the advanced exposure modes. In the meantime, here are my general recommendations:

• Use the lowest possible ISO setting unless the lighting conditions are such that you can’t use the aperture and shutter speed you want without raising the ISO.
• If your subject is moving, give shutter speed the next highest priority in your exposure decision. Choose a fast shutter speed to ensure a blur-free photo or, on the flip side, select a slow shutter speed to intentionally blur that moving object, an effect that can create a heightened sense of motion.

• For nonmoving subjects, make aperture a priority over shutter speed, setting the aperture according to the depth of field you have in mind. For portraits, for example, try using a wide-open aperture (a low f-stop number) to create a short depth of field and a nice, soft background for your subject.

  Be careful not to go too shallow with depth of field when shooting a group portrait. Unless all the subjects are the same distance from the camera, some may be outside the zone of sharp focus. A shallow depth of field also makes action shots more difficult because you have to be absolutely spot on with focus. With a greater depth of field, the subject can move farther toward or away from you before leaving the sharp-focus area, giving you a bit of a focusing safety net.

Keeping all this information straight may be a little overwhelming at first, but the more you work with your camera, the more the whole exposure equation will make sense to you. You can find tips in Chapter 7 for choosing exposure settings for specific types of pictures; keep moving through this chapter for details on how to monitor and adjust aperture, shutter speed, and ISO settings.

Controlling ISO

To recap the basic exposure information presented at the start of this chapter, your camera’s ISO setting controls how sensitive the image sensor is to light. At a higher ISO value, you need less light to expose the image. Remember the downside to raising ISO, however: The higher the ISO, the greater the possibility of noisy images. Refer to Figure 4-5 for a reminder of what that defect looks like.

In Scene Intelligent Auto, Creative Auto, Flash Off, and the scene modes (Portrait, Landscape, and so on), the camera controls ISO. But in the advanced exposure modes, you have the following ISO choices:

• Select a specific ISO setting. Normally, you can choose ISO settings ranging from 100 to 6400. Or if you really want to push things, you can amp ISO up to 12800. In order to take advantage of that option, set Custom Function 2, ISO Expansion, to On, as shown in Figure 4-14. Now when you adjust ISO, an H (for High) appears as a possible setting; select that setting for ISO 12800.

  A few complications to note: If you enable Highlight Tone Priority, an exposure feature covered later in this chapter, you lose the option of using ISO 100 as well as the expanded ISO setting (H, 12800).

• Let the camera choose (Auto ISO). You can ask the camera to adjust ISO for you if you prefer. By default, the camera has the option to raise the ISO as high as 3200, but you can choose a different limit if you prefer. Make the change via the ISO Auto setting on Shooting Menu 3, as shown in Figure 4-15. The low limit is ISO 400; the high limit, ISO 6400, regardless of whether you turn on ISO Expansion.

  Using Auto ISO is especially handy when the light is changing fast or your subject is moving from light to dark areas quickly. In these situations, Auto ISO can save the day, giving you properly exposed images without any ISO futzing on your part.

You can view the current ISO setting in Shooting Settings and Live View displays, as shown in Figure 4-16, as well as in the viewfinder, as shown in Figure 4-17. (If you don’t see the value in Live View mode, press the DISP button to switch to a display mode that presents the data.)

In Auto ISO mode, the Shooting Settings and Live View displays initially show Auto as the ISO value, as you would expect. But when you press the shutter button halfway, which initiates exposure metering, the value changes to show you the ISO setting the camera has selected. You also see the selected value rather than Auto in the viewfinder.

Note: When you view shooting data during playback, you may see a value reported that isn’t on the list of “official” ISO settings — ISO 320, for example. This happens because in Auto mode, the camera can select values all along the available ISO range, whereas if you select a specific ISO setting, you’re restricted to specific notches within the range.

To adjust the ISO setting, you have these options:

• Use the Quick Control screen. After highlighting the ISO option, as shown on the left in Figure 4-18, rotate the Main dial to cycle through the available ISO settings. You also can press Set to display a screen containing all available options, as shown on the right.

  Figure 4-18 shows you how the screens appear during viewfinder shooting; in Live View mode, the ISO option appears in the lower-left corner of the monitor after you press the Q button to shift to the Quick Control display. Again, highlight the ISO setting and either rotate the Main dial to change it or press Set to see all the available options onscreen at once.

• Press the top cross key, labeled ISO (not available in Live View mode). You then see the screen shown on the right in Figure 4-18, where you can choose your desired setting.
• Reconfigure the Flash button to act as an ISO button. For one-button access to the ISO setting during Live View shooting, you can set the Flash button to bring up the ISO settings screen. Make the change via Custom Function 10 (part of the Custom Functions option found on Setup Menu 3). Obviously, if you plan to use the built-in flash, this isn’t a good solution because you then have no way to raise the flash. Assigning the ISO function to the Flash button may be helpful if you’re shooting with an external flash, in which case you don’t need to use the button for any flash-related purpose. But again, you only need to consider this option if you’re shooting in Live View mode because for viewfinder shooting, the top cross key whisks you to the ISO setting screen.

Adjusting aperture and shutter speed

You can adjust aperture and shutter speed only in P, Tv, Av, and M exposure modes. To wake up the exposure meter and view the current f-stop and shutter speed in the displays, press the shutter button halfway. Then use these techniques to adjust the settings, depending on your exposure mode:

• P (programmed autoexposure): The camera displays its recommended combination of aperture and shutter speed. To select a different combination, rotate the Main dial.
• Tv (shutter-priority autoexposure): Rotate the Main dial to set the shutter speed. When not using flash, you can select from a shutter-speed range of 30 seconds to 1/4000 second. As you change the shutter speed, the camera automatically adjusts the aperture setting.

• Av (aperture-priority autoexposure): Rotate the Main dial to change the f-stop setting. As you do, the camera adjusts the shutter speed to produce the proper exposure. How many f-stops are available depend on your lens and, if you’re using a zoom lens, the current focal length (zoom position).

  After changing the aperture, make sure that the shutter speed hasn’t dropped so low that handholding the camera or capturing a moving subject won’t be possible. If this problem arises, use a higher ISO setting, which will enable the camera to select a faster shutter speed.

• M (manual exposure): Select aperture and shutter speed like so:

  • Adjust shutter speed. Rotate the Main dial.

    In Manual mode, you can access one option not available in Tv mode: Rotate the Main dial one notch past the 30-second setting to access Bulb mode. This setting keeps the shutter open for as long as you hold down the shutter button. Bulb mode is great for night photography, catching lightning in action, and photographing thunderstorms or starry skies. It enables you to experiment with different shutter speeds simply by holding the shutter button down for different lengths of time — you don’t have to fiddle with changing the shutter speed between each shot.

  • Adjust aperture. Press and hold the Exposure Compensation button while rotating the Main dial. (See the Av label on the button? That’s your clue to the aperture-related function of the button — Av stands for aperture value.)

In M, Tv, and Av modes, the setting that’s available for adjustment appears in the Shooting Settings display with little arrows at each side. Your camera manual refers to this display as the Main dial pointer, and it’s provided as a reminder that you use the Main dial to change the setting. For example, in M mode, the shutter speed is bordered by the arrows until you hold down the Exposure Compensation button, at which point the marker shifts to the aperture (f-stop) value, as shown in Figure 4-19.

It’s easy to get confused when you shoot in the Av and Tv modes because as you rotate the Main dial to change the f-stop or shutter speed, respectively, the camera changes the other setting automatically. So remember that the pointer arrows indicate the setting that you’re controlling. If the other setting doesn’t change in tandem, you reached the limits of the shutter-speed or aperture range.

When the Shooting Settings screen is displayed, you also can use the Quick Control screen to adjust the settings in the M, Tv, and Av modes. This technique is more cumbersome but comes in handy in M mode because you can adjust the f-stop setting without having to remember what button to push to do the job. The Quick Control method doesn’t work in Live View mode.

A few more words of wisdom related to aperture and shutter speed:

• When using Manual exposure, don’t forget that you can check the exposure meter to get the camera’s take on your exposure settings (when in Live View, look at the monitor for a preview). Of course, you don’t have to follow the camera’s guidance — you can take the picture using any settings you like, even if the meter indicates that the image will be under- or overexposed.

• In P, Tv, and Av mode, the shutter speed or f-stop value blinks if the camera isn’t able to select settings that produce a good exposure. If the problem is too little light, try raising the ISO or adding flash to solve the problem. If there’s too much light, lower the ISO value or attach an ND (neutral density) filter, which is sort of like sunglasses for your lens — it simply cuts the light entering the lens. (The neutral part just means that the filter doesn’t affect image colors, just brightness.)

• When you use P, Tv, and Av modes, the settings that the camera selects are based on what it thinks is the proper exposure. If you don’t agree with the camera, you have two options. Switch to manual exposure (M) mode and dial in the aperture and shutter speed that deliver the exposure you want. Or if you want to stay in P, Tv, or Av mode, try using exposure compensation, one of the exposure-correction tools described in the next section.

Overriding autoexposure results with Exposure Compensation

In the P, S, and A exposure modes, you have some input over exposure. In P mode, you can rotate the Main dial to choose from different combinations of aperture and shutter speed; in Tv mode, you can dial in the shutter speed; and in Av mode, you can select the aperture setting. But because these are semiautomatic modes, the camera ultimately controls the final exposure. If your picture turns out too bright or too dark in P mode, you can’t simply choose a different f-stop/shutter speed combo because they all deliver the same exposure — which is to say, the exposure that the camera has in mind. And changing the shutter speed in Tv mode or adjusting the f-stop in Av mode won’t help either because as soon as you change the setting that you’re controlling, the camera automatically adjusts the other setting to produce the same exposure it initially delivered.

Not to worry: You actually do have final say over exposure in these exposure modes. The secret is Exposure Compensation, a feature that tells the camera to produce a brighter or darker exposure on your next shot, whether or not you change the aperture or shutter speed (or both, in P mode).

Best of all, this feature is probably one of the easiest on the camera to understand. Here’s all there is to it:

• Exposure compensation is stated in EV values, as in +2.0 EV. Possible values range from +5.0 EV to –5.0 EV.

• Each full number on the EV scale represents an exposure shift of one full stop. In plain English, it means that if you change the Exposure Compensation setting from EV 0.0 to EV –1.0, the camera adjusts either the aperture or the shutter speed to allow half as much light into the camera as it would get at the current setting. If you instead raise the value to EV +1.0, the settings are adjusted to double the light.

• A setting of EV 0.0 results in no exposure adjustment.
• For a brighter image, you raise the EV value. The higher you go, the brighter the image becomes.
• For a darker image, you lower the EV value. The picture becomes progressively darker with each step down the EV scale.

Exposure compensation is especially helpful when your subject is much lighter or darker than an average scene. For example, take a look at the image on the left in Figure 4-20. Because of the very bright sky, the camera chose an exposure that I thought made the tree too dark. Setting the Exposure Compensation value to EV +1.0 resulted in a brighter image, allowing the details of the tree to be more visible.

Sometimes you can cope with situations like this one by changing the Metering mode, as discussed earlier in this chapter. But in cases like the shot in Figure 4-20, the results would have been much the same in all the metering modes because the brightest part of the frame — the area that caused the original underexposure — is in the center. That area would have been part of the exposure calculation in all three metering modes. Also, I find that it usually takes more time to experiment with metering modes than to simply adjust exposure compensation to get the results I’m after.

You can take several roads to applying exposure compensation:

• Exposure Compensation button: The fastest option is to press and hold the Exposure Compensation button while rotating the Main dial. As you adjust the setting, the exposure meter in the Shooting Settings and Live View displays indicates the current Exposure Compensation amount. For example, in Figure 4-21, the amount of adjustment is +1.0. The viewfinder meter also displays the amount of adjustment.

  Note that even though the meters initially show a range of just +/– three stops, you can access the entire five-stop range. Just keep rotating the Main dial to display the far ends of the range.

• Quick Control screen (not available in Live View mode): Highlight the exposure meter in the Quick Control display and rotate the Main dial to move the exposure indicator left or right along the meter.

• Shooting Menu 2: Select Expo Comp/AEB, as shown on the left in Figure 4-22, and press Set to display the screen shown on the right in the figure. You can access this same screen by pressing Set when the meter is highlighted on the Quick Control screen.

  Either way, this is a tricky screen, so pay attention:

  • The screen has a double purpose: You use it to enable automatic exposure bracketing (AEB) as well as exposure compensation. So if you’re not careful, you can wind up changing the wrong setting.

  • To apply exposure compensation, press the left/right cross keys to move the exposure indicator (the red line on the meter) along the scale.

    Notice the triangles at the right end of the meter? They’re there to remind you to use the cross keys to make this adjustment. The symbol just below — the jagged half circle — represents the Main dial, which sets up automatic exposure bracketing.

When you dial in an adjustment of greater than three stops, the notch under the viewfinder meter disappears and is replaced by a little triangle at one end of the meter — at the right end for a positive Exposure Compensation value and at the left for a negative value. However, the meter on the Shooting Settings and Live View screens and on Shooting Menu 2 adjust to show the proper setting.

Whatever setting you select, the way that the camera arrives at the brighter or darker image you request depends on the exposure mode:

• In Av (aperture-priority) mode, the camera adjusts the shutter speed but leaves your selected f-stop in force.
• In Tv (shutter-priority) mode, the opposite occurs: The camera opens or stops down the aperture, leaving your selected shutter speed alone.
• In P (programmed autoexposure) mode, the camera decides whether to adjust aperture, shutter speed, or both to accommodate the Exposure Compensation setting.

These explanations assume that you have a specific ISO setting selected rather than Auto ISO. If you do use Auto ISO, the camera may adjust that value instead.

Keep in mind, too, that the camera can adjust the aperture only so much, according to the aperture range of your lens. The range of shutter speeds is limited by the camera; when you use flash, the fastest available shutter speed is 1/200 second. (Otherwise, the shutter speed can go up to 1/4000 second.) If you reach the end of those ranges, you have to compromise on either shutter speed or aperture, or adjust ISO.

A final, and critical, point about exposure compensation: When you power off the camera, it doesn’t return you to a neutral setting (EV 0.0). The setting you last used remains in force for the P, Tv, and Av modes until you change it. So it’s always a good idea to zero out the setting at the end of a shoot.

Improving high-contrast shots with Highlight Tone Priority

When a scene contains both very dark and very bright areas, achieving a good exposure can be difficult. If you choose exposure settings that render the shadows properly, the highlights are often overexposed, as in the left image in Figure 4-23. Although the dark lamppost in the foreground looks fine, the white building behind it has become so bright that all detail has been lost. The same thing occurred in the highlight areas of the green church steeple.

Your camera offers an option that can help produce a better image in this situation — Highlight Tone Priority — which was used to produce the image on the right in Figure 4-23. The difference is subtle, but if you look at that white building and steeple, you can see that the effect does make a difference. Now the windows in the building are at least visible, the steeple has regained some of its color, and the sky, too, has a bit more blue.

This feature is available only in the P, Tv, Av, and M modes. It’s turned off by default, which may seem like an odd choice after looking at the improvement it made to the scene in Figure 4-23. What gives? The answer is that in order to do its thing, Highlight Tone Priority needs to play with a few other camera settings, as follows:

• The ISO range is reduced to ISO 200–6400. The camera needs the more limited range in order to favor the image highlights.
• Auto Lighting Optimizer is automatically disabled. This feature, which attempts to improve image contrast, is incompatible with Highlight Tone Priority. So read the next section, which explains Auto Lighting Optimizer, to determine which of the two exposure tweaks you want to use.
• You can wind up with slightly more noise in shadow areas of the image. Again, noise is the defect that looks like speckles in your image.

The only way to enable Highlight Tone Priority is via Custom Function 6, found on Setup Menu 3 and shown in Figure 4-24.

As a reminder that Highlight Tone Priority is enabled, a D+ symbol appears near the ISO value in the Shooting Settings and Live View displays, as shown in Figure 4-25. The same symbol appears with the ISO setting in the viewfinder and in the shooting data that appears in Playback mode. (See Chapter 9 to find out more about picture playback.) Notice that the symbol that represents Auto Lighting Optimizer is dimmed because that feature is automatically disabled as soon as you turn on Highlight Tone Priority. I labeled the Auto Lighting Optimizer symbol in the figure as well.

Experimenting with Auto Lighting Optimizer

When you select an Image Quality setting that results in a JPEG image file — that is, any setting other than Raw — the camera tries to enhance your photo while it’s processing the picture. Unlike Highlight Tone Priority, which concentrates on preserving highlight detail only, Auto Lighting Optimizer adjusts both shadows and highlights to improve the final image tonality (range of darks to lights). In other words, it’s a contrast adjustment.

In the fully automatic exposure modes as well as in Creative Auto, you have no control over how much adjustment is made. But in P, Tv, Av, and M modes, you can decide whether to enable Auto Lighting Optimizer. You also can request a stronger or lighter application of the effect than the default setting. Figure 4-26 offers an example of the type of impact of each Auto Lighting Optimizer setting.

Given the level of improvement that the Auto Lighting Optimizer correction made to this photo, you may be thinking that you’d be crazy to ever disable the feature. But it’s important to note a few points:

• The level of shift that occurs between each Auto Lighting Optimizer setting varies depending on the subject. This particular example shows a fairly noticeable difference between the Strong and Off settings. But you don’t always see this much impact from the filter. Even in this example, it’s difficult to detect much difference between Off and Low.
• Although the filter improved this particular scene, at times you may not find it beneficial. For example, maybe you’re purposely trying to shoot a backlit subject in silhouette or produce a low-contrast image. Either way, you don’t want the camera to insert its opinions on the exposure or contrast you’re trying to achieve.
• Because the filter is applied after you capture the photo, while the camera is writing the data to the memory card, it can slow your shooting rate.
• In some lighting conditions, Auto Lighting Optimizer can produce an increase in image noise.

• The corrective action taken by Auto Lighting Optimizer can make some other exposure-adjustment features less effective. So turn it off if you don’t see the results you expect when you’re using the following features:

  • Exposure compensation, discussed earlier in this chapter
  • Flash compensation, discussed in Chapter 2
  • Automatic exposure bracketing, also discussed later in this chapter
• You can’t use this feature while Highlight Tone Priority (explained in the preceding section) is enabled.

You can adjust the setting in two ways:

• Quick Control screen: After highlighting the Auto Lighting Optimizer symbol, labeled in Figure 4-27, rotate the Main dial to cycle through the four options. You also can press Set to display a screen showing all the available settings.

• Shooting Menu 2: Select the option and press Set to display the selection screen, as shown on the left in Figure 4-28.

  Notice the little vertical bars in the graphic that represents the Auto Lighting Optimizer setting. The number of bars tells you how much adjustment is being applied. Two bars, as in Figure 4-27, represent the Standard setting, which is the default; three bars, Strong; and one bar, Low. The bars are replaced by the word Off when the feature is disabled.

Correcting lens vignetting with Peripheral Illumination Correction

Some lenses produce pictures that appear darker around the edges of the frame than in the center, even when the lighting is consistent throughout. This phenomenon goes by several names, but the two heard most often are vignetting and light fall-off. How much vignetting occurs depends on the lens, your aperture setting, and the lens focal length.

To help compensate for vignetting, your camera offers Peripheral Illumination Correction, which adjusts image brightness around the edges of the frame. Figure 4-29 shows an example. In the left image, just a slight amount of light fall-off occurs at the corners, most noticeably at the top of the image. The right image shows the same scene with Peripheral Illumination Correction enabled.

Now, this “before” example hardly exhibits serious vignetting — it’s likely that most people wouldn’t even notice if it weren’t shown next to the “after” example. But if your lens suffers from stronger vignetting, Peripheral Illumination Correction can help correct the problem.

The adjustment is available in all your camera’s exposure modes. But a few factoids need spelling out:

• The correction is available only for photos captured in the JPEG file format. For Raw photos, you can choose to apply the correction and vary its strength if you use Canon Digital Photo Professional to process your Raw images. Chapter 10 talks more about Raw processing.

• For the camera to apply the proper correction, data about the specific lens must be included in the camera’s firmware (internal software). You can determine whether your lens is supported by opening Shooting Menu 1 and selecting Peripheral Illumination Correction, as shown on the left in Figure 4-30. Press Set to display the right screen in the figure. If the screen reports that correction data is available, as in the figure, the feature is enabled by default.

  If your lens isn’t supported, you may be able to add its information to the camera; Canon calls this step registering your lens. You do this by using the supplied USB cable to connect the camera to your computer and then using tools included with Canon EOS Utility software. (The software is available for free download from the Canon website; look for the download links in the support section of the site.) I must refer you to the software manual for help on this bit of business because of the limited number of words that can fit in these pages.

• For non-Canon lenses, Canon recommends disabling Peripheral Illumination Correction even if correction data is available. You can still apply the correction in Digital Photo Professional when you shoot in the Raw format.

• In some circumstances, the correction may produce increased noise at the corners of the photo. This problem occurs because exposure adjustment can make noise more apparent. Also, at high ISO settings, the camera applies the filter at a lesser strength — presumably to avoid adding even more noise to the picture. (See the earlier “ISO affects image noise” section and “Dampening noise” sidebar for an understanding of noise and its relationship to ISO.)

Turning auto bracketing on and off

The following steps show you how to turn on Automatic Exposure Bracketing via Shooting Menu 2. (I explain more about another option for enabling the feature momentarily.)

1. Display Shooting Menu 2 and highlight Expo Comp/AEB, as shown on the left in Figure 4-31.

2. Press Set.

   You see a screen like the one shown on the right in Figure 4-31. This is the same dual-natured screen that appears when you apply exposure compensation, as explained earlier in this chapter. In M mode, exposure compensation isn’t relevant — if you want a darker or brighter image, you just adjust the f-stop, shutter speed, or ISO. So the Exposure Compensation controls are dimmed on the Exposure Comp/AEB screen if the Mode dial is set to M.

3. Rotate the Main dial to establish the amount of exposure change you want between images.

   What you see onscreen after you rotate the dial depends on your exposure mode:

   • M mode: The screen changes to look similar to the one on the left in Figure 4-32, with only the AEB setting active. On the little meter, each whole number represents one stop of exposure shift. The little red lines under the meter show you the amount of shift that will occur in your bracketed series of shots. For example, the settings in Figure 4-32 represent one stop of adjustment. No matter what the settings, the first image is captured at the actual exposure settings; the second, at settings that produce a darker image; and the third, at settings that produce a brighter photo.

   • P, Tv, or Av modes: For these modes, both the Exposure Compensation and AEB features are enabled. And the meter expands, as shown on the right in Figure 4-32, to represent the total four-stop adjustment you can make in bracketed shots if you also enable the maximum amount of exposure compensation. (The meter expands after you rotate the Main dial; otherwise, it just shows the five-stop range for exposure compensation.)

     Where does the four-stop thing come from? Well, you’re still limited to adjusting exposure a total of two stops between bracketed shots. However, if you turn on the Exposure Compensation feature and set that value to +5.0 and then set the bracketed amount to +2.0, your brightest shot in the bracketed series is captured at +7.0. Your darkest shot is captured at +3.0.

   Keep rotating the dial until you get the exposure indicators to reflect the amount of adjustment you want between each bracketed shot. (If you want to adjust the Exposure Compensation setting, press the right/left cross keys.)

4. Press Set.

   AEB is now enabled. To remind you of that fact, the exposure meter in the Shooting Settings shows the three exposure indicators to represent the exposure shift you established, as shown in Figure 4-33. You see the same markers on Shooting Menu 2, on the viewfinder meter, and on the meter that appears at the bottom of the screen in Live View mode.

For viewfinder photography, you can also enable AEB through the Quick Control screen. After highlighting the exposure meter, press Set to display a screen that works just like the one you get through the menu. Again, rotate the Main dial to set the bracketing amount and then press Set to wrap things up. In M exposure mode, you don’t even have to press Set; just highlight the meter and rotate the Main dial to set the bracketing amount.

To turn off Automatic Exposure Bracketing, just change the AEB setting back to 0.

AEB is also turned off when you power down the camera, enable the flash, replace the camera battery, or replace the memory card. You also can’t use the feature in manual exposure (M) mode if you set the shutter speed to the Bulb option. (At that setting, the camera keeps the shutter open as long as you press the shutter button.)

Shooting a bracketed series

After you enable auto bracketing, the way you record your trio of bracketed exposures depends on the selected Drive mode. This setting, described in Chapter 2, determines whether the camera records a single image or multiple images with each press of the shutter button. (Press the left cross key to access the screen that enables you to change this setting.)

Here’s how things shake out as far as shooting a bracketed series in each Drive mode:

• AEB in Single mode: You take each exposure separately, pressing the shutter button fully three times to record your trio of images.

  If you forget which exposure you’re taking, look at the exposure meter. After you press the shutter button halfway to lock focus, the meter shows just a single indicator bar instead of three. If the bar is at 0, you’re ready to take the first capture. If it’s to the left of 0, you’re on capture two, which creates the darker exposure. If it’s to the right of 0, you’re on capture three, which produces the brightest image. My advice assumes that you haven’t also applied exposure compensation, in which case the starting point is at a notch other than zero.

• AEB in Continuous mode: Press and hold the shutter button down to record three continuous frames. (Be sure to wait for the camera to record all three frames before you release the shutter button.) To record another series, release and then press the shutter button again. In other words, when AEB is turned on, the camera doesn’t keep recording images until you release the shutter button as it normally does in Continuous mode — you can take only three images with one press of the shutter button.
• Self-Timer modes: In the two standard Self-Timer modes (10-second and 2-second delays), all three exposures are recorded with a single press of the shutter button. But you don’t need to hold down the shutter button as you do in Continuous mode — just press and release. If you set the Drive mode to Self-Timer: Continuous, the camera captures multiple bracketed series, according to how many frames you select for the Self-Timer setting. Set the Self-Timer option to capture 4 frames, for example, and you get four bracketed series, for a total of 12 frames.