Contrast Detection

This is a slower, but potentially more accurate mode, best suited for static subjects, and was originally the only kind of autofocus available for mirrorless cameras and for dSLRs when shooting in their live view and movie modes. The innovation of adding phase detection abilities to the sensor itself (as I’ll describe shortly) made contrast detection a fine-tuning option for hybrid autofocus systems that combined CDAF and PDAF.

Contrast detection is very easy to understand, and is illustrated by Figure 4.1, a close-up of the side of an old barn. At top in the figure, the transitions between the edges found in the siding and foundation image are soft and blurred because of the low contrast between them. Whether the edges are horizontal, vertical (like the siding), or diagonal doesn’t matter in the least; the focus system looks only for contrast between edges, and those edges can run in any direction at all.

At the bottom of Figure 4.1, the image has been brought into sharp focus, and the edges have much more contrast; the transitions are sharp and clear. Although this example is a bit exaggerated so you can see the results on the printed page, it’s easy to understand that when maximum contrast in a subject is achieved, it can be deemed to be in sharp focus. Although achieving focus with contrast detection is generally quite a bit slower, it can be used to fine-tune focus on a subject that has already been brought into general focus using phase detection (described next). There are several advantages—and disadvantages—to contrast detection, and I’ll summarize them shortly.

Phase Detection

Phase detection is easily much more rapid than contrast detection. The challenge is to make its operation as accurate as possible. Digital SLRs have always used PDAF, with an array of tiny autofocus sensors, located in the “floor” of the mirror box, and a small portion of the illumination directed downward to the autofocus sensor array. In the a7 IV, phase detection is built into pixels embedded in the sensor and combines with contrast detection to give us, potentially, the best of both worlds. I’ll show you the location of the PDAF and CDAF areas shortly.

Phase detection is also used in a different way when you use A-mount (rather than E-mount) lenses attached to the optional LA-EA2 or LA-EA4 A-mount lens adapters. Both adapters have their own built-in phase detection autofocus systems that bypass and replace the hybrid AF phase/contrast detection technology built into your camera.

The phase detection pixels in the a7 IV’s sensor split incoming photons arriving from opposite sides of the lens into two parts, forming a pair of images, exactly like the rangefinders used for surveying and in rangefinder-focusing cameras like the venerable Leica M series. The dual images are separated when out of focus, and then gradually brought together to achieve sharp focus, as shown from top to bottom in Figure 4.2.

This process tells the camera when the image pair are “in phase” and aligned. The rangefinder approach of phase detection tells the a7 IV exactly how out of focus the image is, and in which direction (focus is too near, or too far) thanks to the amount and direction of the displacement of the split image. The camera can quickly and precisely snap the image into sharp focus and match the lines. If necessary, the a7 IV’s contrast detect feature can follow up to perfect the plane of focus.

The PDAF sensors in the a7 IV are all line sensors, which means they work best with features that transect the sensor either perpendicularly or at an angle, as visualized in Figure 4.3, left. It’s easy to detect when the two halves of the vertical lines of the weathered wood are aligned. (See Figure 4.3, center.) However, when the same sensor is asked to measure focus for, say, horizontal lines that don’t split up quite so conveniently, or, in the worst case, subjects such as the sky (which may have neither vertical nor horizontal lines), focus can slow down drastically. One such scenario is pictured in Figure 4.3, right. Fortunately, as I mentioned earlier, the a7 IV’s contrast detection AF will come to the rescue and take over where phase detection AF is stymied.

As with any rangefinder-like function, phase detection accuracy is better when the “base length” between the two images is larger. (Think back to your high school trigonometry; you could calculate a distance more accurately when the separation between the two points where the angles were measured was greater.) For that reason, phase detection autofocus is more accurate with larger (wider) lens openings—especially those with maximum f/stops of f/2.8 or better—than with smaller lens openings, and may not work at all when the f/stop is smaller than f/8. As I noted, the a7 IV is able to perform these comparisons very quickly.

Comparing the Two Hybrid Components

The Sony a7 IV autofocus system uses both phase detection autofocus (PDAF) and contrast detection autofocus (CDAF) to provide a combination of fast and accurate AF, together covering virtually all of the frame. Figure 4.4 shows the layout of the autofocus points and zones used. The figure shows the PDAF and CDAF areas overlaid on each other, but I’m illustrating them separately for easy reference. In real life, they work together in tandem.

• ■Phase detection points. The phase detect areas of the a7 IV, represented by the green rectangles at top in Figure 4.4, are spread over a wide area. The zone covered by contrast detection is shown as a dark blue rectangle.
• ■Contrast detection zones. The blue boxes at bottom in Figure 4.4 represent the 425 areas of the sensor used by the a7 IV when deploying contrast detection in full-frame mode. The surrounding area covered by the phase detection points is represented by the green rectangle.
• ■Crop mode coverage. One often-overlooked advantage of using the a7 IV APS-C/Super 35 crop mode is that both the CDAF and PDAF areas cover the entire frame, because the outside area of the sensor is cropped out. (See Figure 4.5.)
  • This effective extended coverage can be useful for sports photographers, who may have subjects in all parts of the image. In general, however, crop mode may not be your best option for fast-moving subjects, especially birds-in-flight, because the a7 IV fills the display with the cropped image, and you lose the ability to “preview” where your subject is before it enters the APS-C “frame.”

The hybrid autofocus system uses both types of AF. The process begins by rapidly focusing using PDAF, because the rangefinder approach always tells the camera whether to move focus closer or farther, and by approximately how much. No hunting is required, which is often the case with contrast detection, which needs to tweak the focus point until it settles on the sharpest position.

Once the PDAF has done its stuff, contrast detection kicks in, using its finicky but more accurate focusing capabilities to fine-tune focus. So, you end up with speedy initial focus (PDAF) and slightly slower final adjustments (CDAF), providing a perfect hybrid compromise. That’s why Sony didn’t switch to phase detection completely. Here’s a quick rundown of the advantages of a hybrid system:

• ■Contrast detection works with more image types. Contrast detection doesn’t require subject matter to have lines that are at angles to the PDAF points to work optimally, as phase detection does. Any subject that has edges running in any direction can be used to achieve sharp focus.
• ■Contrast detection can focus on larger areas of the scene. Whereas phase detection focus can be achieved only at the points that fall on one of the special autofocus sensor pixels, with contrast detection much larger portions of the image can be used as focus zones. Focus is achieved with the actual sensor image, so focus point selection is simply a matter of choosing which part of the sensor image to use.
• ■Contrast detection can be more accurate with some types of scenes. Phase detection can fall prey to the vagaries of uncooperative subject matter: if suitable lines aren’t available, the system may achieve less than optimal focus. In addition, accuracy decreases as the maximum aperture baseline used for calculations becomes smaller. A lens with a maximum aperture of f/5.6 will focus with less accuracy than one with an f/1.8 maximum aperture. Contrast detection focus is more clear-cut. In most cases, the camera is able to determine clearly when sharp focus has been achieved.
• ■Phase detection “knows” which direction to focus. The split image seen by phase detection sensors reveal instantly whether focus is too close or too far. There is no need to “hunt” for the focus point, as the AF system can immediately adjust in the proper direction. That boosts focus speed considerably.
• ■Phase detection “knows” how far out of focus a subject is. The separation between the two halves of the image let the AF system know whether the subject is grossly out of focus, or whether only a slight adjustment is needed. That means faster autofocus, too.
• ■Phase detection isn’t as dependent on scene brightness. As long as the split images are illuminated well enough for the AF system to make an evaluation, greater or lesser amounts of light don’t have as much of an effect on speed and accuracy. Remember, the reason phase detection systems operate less well at smaller f/stops is because the baseline diameter of the aperture is smaller.
• ■Sony’s 4D high-density tracking can follow moving subjects. The a7 IV’s phase detection system can achieve focus quickly (even when shooting continuously at 10 frames per second), whether your subject is moving horizontally or vertically (what Sony calls area), toward you, or away from you (depth in Sony-speak). To those three dimensions, the system adds the fourth dimension of time (which the company labels as steadfast), so focus can be maintained as it changes position. The 4D AF also deploys high-density tracking to zero in on moving subjects, using focus areas that are smaller than the phase detection sensor areas shown in Figure 4.4.

Focus Modes and Options

Now that you understand the fundamental principles of how the a7 IV achieves focus, let’s discuss the practical application of these principles to your everyday picture-taking activities, by setting the various modes and options available for the autofocus system. We’ll also discuss the use of manual focus, and when that method might be preferable to autofocus.

As you’ve come to appreciate by now, the a7 IV offers many options for your photography. Focus is no exception. Of course, as with other aspects of this camera, you can set the shooting mode to Intelligent Auto or Program mode, and the camera will do just fine in most situations. But, if you want more creative control, the choices are there for you to make.

So, no matter what shooting mode you’re using, your first choice is whether to use autofocus or manual focus. Yes, there’s also a Direct Manual Focus (DMF) option, but that still provides autofocus, with the option of fine-tuning focus manually before taking the shot. Manual focus presents you with great flexibility along with the challenge of keeping the image in focus under what may be difficult conditions, such as rapid motion of the subject, darkness of the scene, and the like. Later in this chapter, I’ll cover manual focus as well as DMF. For now, I’ll assume you’re going to rely on the camera’s conventional AF mode.

The Sony a7 IV has three basic AF modes: AF-S (Single-shot autofocus) and AF-C (Continuous autofocus), as well as Automatic AF (AF-A), which switches between the two other modes as required. Once you have decided on which of these to use, you also need to tell the camera how to select the area used to measure AF. In other words, after you tell the camera how to autofocus, you also have to tell it where to direct its focusing attention.

Adding Circles of Confusion

But there are other factors in play, as well. You know that increased depth-of-field brings more of your subject into focus. But more depth-of-field also makes autofocusing (or manual focusing) more difficult because the contrast is lower between objects at different distances. So, autofocus with a 300mm lens (or zoom setting) may be easier than at a 16mm focal length (or zoom setting) because the longer lens has less apparent depth-of-field. By the same token, a lens with a maximum aperture of f/1.8 will be easier to autofocus (or manually focus) than one of the same focal length with an f/4 maximum aperture, because the f/4 lens has more depth-of-field and a dimmer view. It’s also important to note that lenses with a maximum aperture smaller than f/5.6 would give your Alpha’s autofocus system fits, because the smaller opening (aperture) would allow less light to enter or to reach the autofocus sensor.

Technically, there is just one plane within your picture area, parallel to the back of the camera (or sensor, in the case of a digital camera), that is in sharp focus. That’s the plane in which the points of the image are rendered as precise points. At every other plane in front of or behind the focus plane, the points show up as discs that range from slightly blurry to extremely blurry. In practice, the discs in many of these planes will still be so small that we see them as points, and that’s where we get depth-of-field. Depth-of-field is just the range of planes that include discs that we perceive as points rather than blurred splotches. The size of this range increases as the aperture is reduced in size and is allocated roughly one-third in front of the plane of sharpest focus, and two-thirds behind it. The range of sharp focus is always greater behind your subject than in front of it. (See Figure 4.6.)

To make things even more complicated, many subjects aren’t polite enough to remain still. They move around in the frame, so that even if the camera’s lens is sharply focused on your main subject, the subject may change position and require refocusing. An intervening subject may pop into the frame and pass between you and the subject you meant to photograph. You (or the camera) have to decide whether to focus on this new subject, or to remain focused on the original subject. Finally, there are some kinds of subjects that are difficult to bring into sharp focus because they lack enough contrast to allow the camera’s AF system (or our eyes) to lock in. Blank walls, a clear blue sky, or other low-contrast subject matter may make focusing difficult even with the hybrid AF system.

If you find all these focus factors confusing, you’re on the right track. Focus is, in fact, measured using something called a circle of confusion. An ideal image consists of zillions of tiny little points, which, like all points, theoretically have no height or width. There is perfect contrast between the point and its surroundings. You can think of each point as a pinpoint of light in a darkened room. When a given point is out of focus, its edges decrease in contrast and it changes from a perfect point to a tiny disc with blurry edges (remember, blur is the lack of contrast between boundaries in an image). (See Figure 4.7.)

If this blurry disc—the circle of confusion—is small enough, our eyes still perceive it as a point. It’s only when the disc grows large enough that we can see it as a blur rather than as a sharp point that a given point is viewed as being out of focus. You can see, then, that enlarging an image, either by displaying it larger on your computer monitor or by making a large print, also magnifies the size of each circle of confusion. Moving closer to the image does the same thing. So, parts of an image that may look perfectly sharp in a 5 × 7-inch print viewed at arm’s length, might appear blurry when blown up to 11 x 14 inches and examined at the same distance. Take a few steps back, however, and the image may look sharp again.

To a lesser extent, the viewer also affects the apparent size of these circles of confusion. Some people see details better at a given distance and may perceive smaller circles of confusion than someone standing next to them. For the most part, however, such differences are small. Truly blurry images will look blurry to just about everyone under the same conditions.

Your Focus Mode Options

Manual focus can come in handy, as I’ll explain later in this chapter, but autofocus is likely to be your choice in the great majority of shooting situations. Choosing the right AF mode and the way in which focus points are selected is your key to success. Using the wrong mode for a particular type of photography can lead to a series of pictures that are all sharply focused—on the wrong subject.

But autofocus isn’t some mindless beast out there snapping your pictures in and out of focus with no feedback from you. There are several settings you can modify to regain a fair amount of control. Your first decision should be which of the autofocus modes to select: Single-shot (AF-S), Continuous AF (AF-C), or Automatic AF (AF-A). DMF first uses autofocus, and then allows you to fine-tune focus manually. I recommend using the Function menu, where Focus Mode is located in the top row, second from the left.

In the next sections, I’m going to describe all five focus modes, so you’ll understand exactly what types of subjects each is intended for. However, as you’ll learn, the a7 IV’s AF system is so sophisticated that you can generally set up your camera as I’ll explain later in this chapter in a section called “Magic Autofocus—Set and Forget,” and then forget about twiddling with autofocus thereafter. I’ll list a few settings you can make that will let the a7 IV easily nail autofocus under most conditions more than 90 percent of the time.

Focus or Release Priority?

The current focus plane is fixed and cannot be changed at a certain point in the picture-taking process. With AF-S mode, that point is when you press the shutter release halfway. As long as you keep your finger on the button, the camera will not refocus until you press down all the way, or take your finger off the release. In AF-C mode, the camera will focus, but will continue to refocus as long as the shutter release is held down halfway. Focus is not locked until you press down all the way to take a picture.

In either mode, when you simply press the shutter release down all the way, focus activation, locking, and picture taking take place one after the other. That’s where focus/release priority come into play. When the shutter release is pressed down all the way in a continuous motion, do you want the camera to wait until sharp focus is achieved, even if that means missing the exact instant you wanted to capture? Or do you want to have the a7 IV go ahead and take the picture anyway, even if there is a possibility that the image isn’t perfectly focused? I’ll explain how to set the priority options in

Chapter 8, but here’s a preview to using the Priority Set in AF-S/AF-C entries in the Focus > AF/ MF > Priority Set in AF-S/AF-C entries:

• ■AF Priority. The shutter is not activated until sharp focus is achieved. You can choose the AF Priority option for both AF-S and AF-C modes individually. Use AF Priority for subjects that are not moving rapidly. The a7 IV’s AF system is fast enough that the slight delay should be negligible. However, if you’re using an A-mount lens that does not have a built-in AF motor with the EA-LA adapter, you can experience a significant delay. Sports shooters and others who depend on capturing the decisive moment and can countenance no delay at all generally use Release Priority, discussed next.
• ■Release Priority. When this option is selected, the shutter is activated when the release button is pushed down all the way in both AF-S and AF-C modes, even if sharp focus has not yet been achieved. I prefer this option for AF-C mode, as Continuous Focus focuses and refocuses constantly when autofocus is active, and even though an image may not quite be in sharpest focus, at least I am able to get my shot. Using Release Priority does not mean that your image won’t be sharply focused; it just means that the a7 IV hasn’t yet confirmed that focus is achieved. Keep in mind that the a7 IV’s AF system is very speedy, so your picture is likely to be in sharp focus even if the camera hasn’t had quite enough time to confirm that focus is locked in. If you’ve been poised with the shutter release pressed halfway, the camera probably has been tracking the focus of your image.
• ■Balanced Emphasis. In this mode, the shutter is released when the button is pressed, with a slight pause if autofocus has not yet been achieved. It can be selected for both AF-S and AF-C modes, and is probably your best choice if you want a good compromise between speed of activation and sharpest focus. However, you would not want to use this setting if the highest possible continuous shooting rates are important to you.

Autofocus Magnified

Your a7 IV has several focusing aids that are activated when you use Manual focus. One of them is a Focus Magnifier tool, which also happens to work perfectly well in autofocus mode. The magnifier can be invoked to enlarge your image so the AF system can more easily zero in on your subject. All you need to do is create a custom key that will produce the Focus Magnifier on demand. Just follow these steps:

• 1.Define a custom key, as the activating button for Focus Magnifier. You’ll find instructions for creating custom keys using the Setup > Operation Customize > Custom Key/Dial Settings entry in Chapter 9. I won’t repeat that information here. Select a button of your choice and choose Focus Magnifier as its custom operation.
• 2.Press the Focus Magnifier custom key. An orange box will appear on the screen. (See Figure 4.9, left.) Use the directional buttons to position the orange box over the area you want to bring into focus.
• 3.Press the center button. The Focus Magnifier will enlarge the image contained within the orange box by a factor of 5.5X. (See Figure 4.9, right.) Press the center button a second time to enlarge 11X, if needed.

• 4.Activate AF. Press the shutter release halfway to activate autofocus (or use another key you may have defined to perform that function, say, if you’re using back-button focus as described later in this chapter).
• 5.AF focus commences. The a7 IV will use the current AF settings to focus on the area you’ve selected with the orange box.

Choosing the AF Area

So far, you have allowed the camera to choose which part of the scene will be in the sharpest focus using its focus detection points (called AF areas by Sony). However, you can also specify a single focus detection point that will be active. The Custom 2 (C2) button will summon Focus Area if you haven’t redefined it to another behavior. You can also specify focus area using the Function menu, using the third icon from the left in the top row. Here is how the AF Area options work:

• ■Wide. The camera chooses the appropriate focus area(s) in order to set focus on a certain subject in the scene. There are no focus indicators visible on the screen until you press the shutter release button halfway. At that point, in AF-S mode, the camera displays one or more green focus indicators to show what area(s) of the image it has used to set focus on. In AF-C mode, the indicators will continue to flicker around the frame while the camera refocuses as necessary. If Face Detection is active, the AF system will prioritize faces when making its decision as to where it should set focus. You’ll see multiple focus indicators when several parts of the scene are at the same distance from the camera. When most of the elements of a scene are at roughly the same distance, the camera displays a single, large green focus bracket around the entire edge of the screen.
  • Even if you set one of the other options, Wide is automatically selected in Intelligent Auto mode. Use this mode to give the camera complete control over where to focus. You can activate AF/ MF > Focus Area > AF-C Area Display, as described in Chapter 8, if you want to see the focus area displayed as you use AF-C. Indeed, if you’re working with AF-C, you’ll see the high-density points “dance” as the a7 IV continually refocuses as your subject or camera moves.

• ■Zone. There are nine different focus zones available—three at the top left, center, and top right of the frame, three in the equivalent positions at the bottom, and three in the middle. Each of those zones is populated by a 9 × 9 array of focus points, as shown in Figure 4.11.
  • You can move the focus array to one of the nine overlapping areas using the directional buttons while those brackets are displayed. To lock the brackets in their current position, press the center button (or other defined Focus Standard button). Press the center button again to resume moving the frames. You can also move the focusing frame quickly with the touch screen and return the zone to the center of the screen by pressing the Trash button.
  • Press the AF-ON button or press the shutter release halfway to initiate focus. The display changes to one of the three modes described in the Vanishing Brackets sidebar above, and the camera chooses which sections within the zone to use to calculate sharp focus. The active focus points will be highlighted in green. Use this mode when you know your subject is going to reside in a largish area of the frame and want to allow the a7 IV to select the exact focus point within your designated zone.

• ■Center Fix. Activate this AF area and the camera will use only a single focus detection point in the center of the frame to set focus. Initially, a pair of black focus brackets appears on the screen. Touch the shutter release button and the camera sets and locks focus on the subject in the center of the image area; the brackets then turn green to confirm the area that will be in the sharpest focus in your image. Choose this option if you want the camera to always focus on the subject in the center of the frame. (See Figure 4.12.) Center the primary subject (like a friend’s face in a wide-angle landscape composition), allow the camera to focus on it, maintain slight pressure on the shutter release button to keep focus locked, and re-frame the scene for a more effective, off-center, composition. Take the photo at any time and your friend (who is now off-center) will be in the sharpest focus.
• ■Spot. This mode enables you to move the camera’s focus detection point (focus area) around the scene to any one of multiple locations, using the directional buttons. When opting for Spot, you can use the left/right buttons to choose Small, Medium, or Large spots, which changes the size of the focus brackets in the frame. This mode can be useful when the camera is mounted on a tripod and you’ll be taking photos of the same scene for a long time while the light is changing, for example. Move the focus area to cover the most important subject, and it will always focus on that point when you later take a photo.
  • Use the multi-selector joystick to move the brackets around the screen, which allows great versatility in the placement of the active focus detection point. (See Figure 4.13.) Adjust the brackets until they cover the most important subject area and touch the shutter release button. The brackets will turn green and the camera will beep to confirm that focus has been set on the intended area.
• ■Expand Spot. If the camera is unable to lock in focus using the selected focus point, it will also use the eight adjacent points to try to achieve focus.
• ■Tracking AF. In this mode, the camera locks focus onto the subject area that is under the selected focus spot when the shutter button is depressed halfway. Then, if the subject moves (or you change the framing in the camera), the camera will continue to refocus on that subject. You can select this mode only when the focus mode is set to Continuous AF (AF-C).

This option is especially powerful, because you can activate it for any of the focus area options described above. That is, once you’ve highlighted Tracking on the selection screen, you can then press the left-right directional button and choose Wide, Zone, Center Fix, Spot, or Expand Spot. The camera will lock on a subject, using one of those area modes to follow it. (See Figure 4.14 and the explanation which follows in the next section.)

You cannot use this option if the Still/Movie/S&Q dial is set to Movies or S&Q quick-/slow-motion video shooting movies. I’ll describe Tracking AF, along with eye/face recognition in more detail in the section that follows this one.

Just as you’re limited in the use of the AF mode in certain operating modes, there’s a limitation with AF Area as well. For example, Spot is not available for selection in Intelligent Auto mode; the camera will always use Multi as the AF Area mode.

Face Detection and Eye AF Overview

As hinted already, the a7 IV has a couple more tricks up its sleeve for setting the AF area. The camera can detect faces and eyes, lets you select which eye to track, and can differentiate between humans and animals—and it can do all that at high speed! You can turn Face Priority on or off and activate visible frames around the faces the a7 IV detects. This enables the camera to attempt to identify any human faces in the scene. If it finds one or more faces, the camera will surround each one (up to eight in all) with the highest priority face outlined in white, and the others in either gray (if an unregistered face) or purple (if you have previously registered that face). In AF-S mode, an additional frame will be placed on the eyes of your subject, if detected. Press the shutter release halfway and the camera focuses on the highest priority face.

You can also specify Face Priority in Multi Metering in the Exposure/Color > Metering group, and the a7 IV will not only try to focus on faces, it will base its exposure on them as well. (It’s locked to On when using Intelligent Auto.) This feature is disabled when Focus > Face/Eye Subject is set to Animal or Bird.

Face/Eye Detection is disabled when using digital zoom features, and the focus magnifier. It’s also unavailable when shooting movies with the 120p/100p Record Setting, S&Q slow-motion movies at 120/100 frames per second, or when capturing 4K movies at 30/25p 100M or 30/25p 60M.

Making Your Face/Eye Detection Settings

The key Face/Eye Detection settings are found in several different menus. This section will help you find and adjust all of them. I’ll show you how to tell the a7 IV to base its AF decisions on faces, give certain faces a higher priority, and explain how to switch back and forth between detecting human eyes and those of animals or birds. Your first stop should be the Focus > Face/Eye AF group, which has six menu entries (See Figure 4.16):

• ■Face/Eye Priority in AF. The entry has two choices: On or Off. When set to Off, the camera gives no special priority to faces detected within the frame. Perhaps you’re shooting landscapes or other scenes and don’t want the camera to fixate on any faces it detects.
  • Alternatively, choose On and the a7 IV will give a higher priority to detected faces. Up to eight faces, if present, may be detected. When autofocus is activated, the camera will attempt to focus on the eyes, if they are located within the active focus area. Note that when using Intelligent Auto, Face/Eye Priority is locked at On.
  • They Eye AF portion of Face/Eye Priority AF may not function as expected with subjects which are rapidly moving, have long bangs, closed eyes, or are wearing sunglasses. Shady conditions, backlight, and low-light situations can also hinder eye detection. Keep in mind that if the a7 IV is unable to focus on human eyes in the frame for some reason, it will fall back to focusing on the human’s face instead. (This is useful with humans who have their eyes closed, are wearing some kinds of glasses, or who have hair that obscures their eyes. You can generally count on having to manually focus Saul “Slash” Hudson.)

• ■Face/Eye Subject. When set to Human, the camera looks for human faces and eyes. If you choose Animal or Bird instead, it looks for animal/bird eyes only; as, to date, the faces of other types of living creates vary too much for existing technology to detect with any reliability. It’s generally safe to leave this setting at Human, unless you happen to be at a zoo, photographing the Westminster Kennel Club show, or engaged in other animal-intensive activities. (Animal/Bird eye detection works great, by the way.)
• ■Subject Selection Setting. This setting allows you to disable one or more of the subject possibilities, Human, Animal, or Bird. For example, if you rarely shoot birds, you can disable that choice so the a7 IV will switch only between Human or Animal subjects using the Face/Eye Subject entry above.
• ■Right/Left Eye Select. Chooses whether to detect the left or right eye of the human subject (the option is not available when Animal is selected for Subject Detection). Note that this feature uses the subject’s eye, which may be on the opposite side from your perspective (that is, your subject’s right eye is on the left side of your frame). In general, it usually doesn’t matter which eye the camera scrutinizes. If you don’t care (which will usually be the case), select Auto instead of Right or Left, and the a7 IV will do a good job of finding the closest eye for you.
  • One really cool thing to do (because you can!) is to assign Switch Right/Left Eye to a Custom Key in the Setup > Operation Customize > Custom Key Setting (Stills) entry, just to have the power to alternate eyes on the fly if you feel the need.
• ■Face/Eye Frame Display. When activated, the camera automatically shows a small white square around a human eye it is focusing on, and that frame will turn green when the subject is in focus. But you can also enable a frame around entire faces with this option. (If you want the frames to display, but disappear after a time, use AF Area Auto Clear, described later in this chapter.)
  • Although the eye-focus box is helpful, I find the additional box around the face very useful and leave it on at all times so I know exactly what face(s) has been detected. When enabled, a gray selection box appears around detected faces. The box around the face used for autofocus turns white. If there are several faces in the frame and you’ve registered and prioritized some or all of them, the boxes around the other faces turn reddish-purple. (I’ll show you how to register faces later in this chapter.) If you find the boxes distracting, you can turn them off, and face detection, if enabled, as described earlier, will still be active.
• ■Face Memory. You can tell your a7 IV which faces are near and dear to your heart using this entry, which allows you to register up to eight different faces. I’ll show you how to capture and prioritize faces in Chapter 8. You can change the preferred order of importance at any time.
• ■Register Faces Priority. This entry lets you enable/disable use of face priority at will. If you’re photographing an event and don’t want to prioritize certain faces (say, you’re at a cousin’s wedding reception and would rather not highlight your immediate family who might be in some of the photos), you can disable registered face priority.

Your AF-C to AF-S Switch

Sony doesn’t offer a Custom Key definition to toggle between AF-C and AF-S, but you can do the next best thing—define a button so that the camera switches to AF-S while you hold down the button and then switches back to AF-C once you release it.

The procedure is fairly simple. Just follow these steps:

• 1.Access Register Custom Shoot Set. Navigate to Shooting > Shooting Mode > Register Custom Shooting Setting (described in more detail in Chapter 6 if you need some coaching).
• 2.Select a Custom Shoot Set to register. I selected Recall Custom Hold 1. Press the center button to enter the setup screen.
• 3.Unmark all but two settings. A wide variety of camera settings can be registered, but for this application we don’t want to mess with most of your camera’s settings. We only want to change the Focus Mode and Focus Area settings, and only while the defined Custom Key is pressed. Scroll through the list and unmark all of them except for Focus Mode and Focus Area.
• 4.Specify each of the two. Highlight Focus Mode and select Single-shot AF from the screen that appears. Then Highlight Focus Area, and choose Center.
• 5.Select Register. Scroll down to the bottom of the settings list and highlight Register. Press the center button to confirm your settings, and MENU to exit.
• 6.Navigate to Setup > Operation Customize and choose Custom Key (Stills).
• 7.Define the button you want to use to switch temporarily to AF-S. I chose the Multi-selector center button.
• 8.When your button is highlighted press the center button, and in the screen that appears navigate to the Recall Custom Hold 1 option.
• 9.Press enter to confirm. Then press MENU to exit.

That’s all there is to it. Henceforth, AF-C, Tracking, and Face/Eye Detection will by default be active and provide amazing AF performance under most circumstances. If you want to switch to AF-S to lock in focus on a specific subject, just press your defined Custom Key (in my case the multi-selector button) and hold it down. Then, press the shutter release halfway. The a7 IV will use Single-shot (AF-S) to focus and the Focus Area will be set to the center of the screen. The camera will lock focus as long as you keep the Custom Key and shutter release depressed. To return to AF-C and your other previous AF settings, just release the Custom Key.

Activating Back-Button Focus

To enable back-button focus, just follow these steps:

• 1.Select an AF-ON button. The a7 IV’s built-in AF-ON button performs this function by default, but if you don’t care for its location next to the viewfinder, you can redefine the AEL button or another key. In the Setup > Operation Customize > Custom Key (Stills) entry, define the button of your choice.
• 2.Turn off shutter button AF activation. In the Focus > AF/MF > AF with Shutter entry, set AF/w Shutter to Off. When you want to disable back-button focus (temporarily or permanently), change it back to On.

That’s all there is to it. Henceforth, pressing the shutter release will not activate autofocus. Autoexposure metering will still be initiated by pressing the button halfway, as long as Exposure/Color > Metering > AEL/w Shutter is set to Auto or On (and not Off) and pressing it all the way takes a picture.