Rudy Winston
Rudy Winston

Rudy Winston has over 14 years experience with Canon USA's Pro Products team, and has been responsible during that time for training Canon's staff on new products, creating presentations for customers and dealers, numerous writing projects, and providing technical assistance to professional and amateur photographers.

EOS 7D: Sophisticated, Customizable AF System

March 29, 2011

Zone AF has the potential to be especially useful for action photographers, shooting subjects ranging from track and field to birds in flight.
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Canon's EOS 7D clearly targets the highest end SLR enthusiast as well as working professionals, with a rich feature set, excellent performance, and superior design. Among its powerful features is its autofocus system, which in some ways is unlike any previous AF system in a Canon EOS SLR. In particular, there’s a diverse new set of options for selecting an area of the image to focus upon. With numerous new features, it’s important for prospective users to have a clear idea of what these different new options are, and how they can be harnessed to create great pictures. We’ll explore that in this assessment of the Canon EOS 7D’s AF system.

Fundamentals:

The actual AF system in the EOS 7D is entirely new to the Canon line, with an AF sensor having 19 cross-type AF points. Each and every point, including those located farthest from the center, is a standard-precision cross-type sensor, which can be used with any lens (or lens plus extender combination) with effective maximum apertures of f/5.6 or faster. Like the EOS 60D and 50D before that, the center AF point also has a separate, diagonal pair of high-precision line sensors, which provide even greater precision; these are automatically used with lenses f/2.8 or faster.

The actual side-to-side coverage of the 19 AF points is the same as on the EOS 60D or 50D, in terms of how far from center they spread. However, they obviously provide much more dense AF coverage than the EOS 60D or 5D series models.

With these densely-packed AF points, new features have become a reality. In many ways, this is the most sophisticated AF system ever in an EOS digital SLR, in some ways surpassing the flexibility of Canon’s top-of-the-line EOS-1D and EOS-1Ds series cameras.

AF modes — One Shot AF and AI Servo AF:

In this case, there is no real change here from previous EOS models:

One-Shot AF: For readers who are new to Canon EOS SLRs, One-Shot AF means the AF system is set to focus upon a stationary subject, and then lock focus upon it once sharp focus has been confirmed. (One-Shot AF has nothing to do with whether you take one or a sequence of pictures.) If the user keeps his/her finger on the shutter release button, focus remains locked, making it easy to lock focus and re-compose to move a subject.

AI Servo AF: This AF mode sets the camera to follow-focus on a moving subject, whether it’s moving slowly, or at the speed of an Indy race car. The camera expects to see, detect and track subject movement whenever you’re in AI Servo AF.

There’s a separate button on top of the camera, similar to other EOS cameras like the EOS 60D or 5D Mark II, marked “AF•Drive”. Press this button, and then turn the top Main Dial to move between One Shot AF and AI Servo. There’s a third option, AI Focus AF, that lets the camera automatically pick between the two.

The viewfinder:

We’ll mention this because the intelligent viewfinder of the EOS 7D is the first ever in the Canon EOS series to have a permanently built-in LCD overlay, which puts black outlines onto the focusing screen on-demand or as needed. AF points, Spot metering circle, and grid lines are among the items that this LCD overlay can display. Furthermore, the LCD outlines can be illuminated red, so they can be visible even in total darkness. Both the red illumination, and the entire viewfinder overlay, can be turned off if the photographer wants or needs a totally clear view of his or her subject.

The intelligent viewfinder is an important part of the AF system, because it’s here that you’ll see the new AF point selection modes come into play, right before your eyes.

With the new M.Fn button, after you’ve first pressed the rear AF point select button, each press of the M.Fn button toggles you through a diverse choice of AF areas:

The M.Fn button:

Immediately adjacent to the shutter button is a small button labeled “M.Fn”. This Multi-function button is a key component of AF area selection and operation. Once you press the AF Point select button, if you then press this new M.Fn button, you toggle between each of the different AF area options — a first for EOS cameras. Previously, to go from Manual AF point selection to Automatic, you’d press the AF point select button on back of the camera, and then turn a dial until the selected individual point in the viewfinder ran to the outer edge of the AF point display; one more click would have all the points or a surrounding ring of points light-up, indicating you were in Automatic AF point selection mode. That’s not the case with the EOS 7D.

With the new M.Fn button, after you’ve first pressed the rear AF point select button, each press of the M.Fn button toggles you through a diverse choice of AF areas:

  • Manual AF point selection mode
  • Spot AF point selection mode
  • AF point expansion mode
  • Automatic AF point selection mode
  • Zone AF mode

We’ll give an overview of each of these. For now, understand that the Multi-function button is the key to access these modes when you’re shooting.

They can also be selected via the Quick Control Screen menu — accessed during shooting by pressing the rear Quick Control Setting button, labeled with a “Q”.

Enabling or disabling AF Area selection options:

Out of the box, the EOS 7D's factory default settings are to have both AF Point Expansion mode and Spot AF mode disabled — but they’re easy to activate, and have available any time you cycle through the various AF Area options.

Go to Custom Function III-6 (“Select AF area selec. mode”. Press the SET button, to move the orange highlighting from the number “6” up top to the Disable-Enable-Register row. Turn the rear Quick Control Dial to highlight “Register”. Press the SET button again.

Now, scroll through the options, and any that are un-checked, press SET to display a check-mark next to them, if you’d like them active.

Finally, scroll to the word “Apply”, be sure it’s highlighted in orange, and then press the SET button. One last step — the highlighting immediately transfers to the word “Enable”. Press the SET button one final time; this locks-in your choices.

For first-time users, who want to experiment and practice with the EOS 7D’s features and capabilities, we’d suggest having all options active (a check-mark next to each one). This document presumes that all AF Area selection options are active.

Manual AF point selection:

This is a basic, fundamental setting that most serious EOS shooters are familiar with. Manual AF point selection allows you to pick ONE AF point. You can freely select any of the 19 AF points, whether it’s the center point, or any one of the outer ones. By definition, Manual AF point selection involves picking and using only one AF point at a time.

Manual AF point selection remains very effective for forcing the camera to focus upon a fairly small and precise part of a subject or scene. Unlike with Automatic AF point selection, there’s never any worry that the camera might focus on something other than where you’re aiming it at. With the EOS 7D, a single AF point, visible in black (or illuminated red) in the viewfinder indicates clearly where the camera is looking to focus.

To activate Manual AF point selection, press the rear AF point selection button, and then quickly press the M.Fn button until you see a single AF rectangle outlined in the finder. Now, using either of the camera’s dials, or the Multi-controller on the rear, you’re free to move that single AF point anywhere you like. Once you stop and tap the shutter button half-way, the camera is ready to shoot, using only that AF point. This will be familiar to users of any previous EOS digital SLR.

Spot AF mode:

The first totally new option with the EOS 7D. You can manually choose any single AF point (as outlined immediately above), but now actually reduce the size of that AF point. This allows you to read an even smaller area of the subject, and focus even more precisely on one particular element in a scene — such as the nearest eye in a portrait, or a precise part of a flower in a macro photograph.

When Spot AF is active, a small secondary box appears inside of the manually-chosen AF point, so you see a “box within a box” in the viewfinder. Like with Manual AF point selection, you can freely choose any of the 19 AF points for Spot AF, whether in the center or off-center. With Spot AF, like Manual AF point selection, you’re only using ONE AF point at a time.

A couple of important notes about Spot AF: While the AF point size is definitely reduced compared to ordinary Manual AF point selection, it’s not the tiny square you see in the finder. The actual area being sampled by the AF sensor is larger than that inner box, so allow for that when composing and shooting. Also, dual-axis, cross-type sensitivity remains at all AF points if you select Spot AF mode, so there’s no loss of effectiveness there.

The benefit of Spot AF — its ability to let you pin-point focus upon a tiny area of a scene — has obvious potential benefits and applications, and we’re sure advanced users and pros will come to appreciate this new feature. But this can have a possible downside, too. By forcing AF upon only a tiny area of your subject, if that happens to fall upon a part of your subject that’s relatively plain, solid and lacking detail, the AF system may have trouble focusing upon it. This can be a real problem with fast moving subjects, especially if they’re moving erratically. At times like these, actually having a larger area can be a more effective way to shoot.

AF Point Expansion:

This is a feature that’s been available on EOS models with the 45-point AF system, like the EOS-1D series cameras. Now, for the first time, it’s available to users in a mid-range model. AF Point Expansion allows the user to manually choose any one AF point to be the primary point he or she wants to use to focus on their subjects. Again, it can be the center point, or any off-center point. But now, additional surrounding points are active, and if the primary point for any reason loses sight of the subject, or can’t find sufficient detail, the surrounding AF points are immediately called-in to assist in focusing upon the subject. This occurs whether you’re shooting a stationary subject in One-Shot AF mode, or tracking a moving subject in AI Servo AF. In fact, AF Point Expansion can be very useful for sports photography and other moving subjects, especially if there’s concern that your AF point may pick up plain, solid areas of a player’s uniform, an animal’s body, and so on.

The number and location of surrounding AF points will vary, depending upon which primary AF point you’ve manually selected. Also, there’s no way to add or subtract these additional surrounding AF points when in AF Point Expansion mode. Fortunately, the camera’s intelligent viewfinder does display the added expanded points — your primary AF point appears as one rectangle, while during selection, the added expanded points appear with both the standard AF box and smaller spot AF box. So it’s never a mystery where these added points are, during both selection and shooting.

Again, during actual shooting, the camera will always try to focus using the one primary AF point you’ve chosen. So it remains an effective tool when you want the camera to focus on one area whenever that’s possible — for example, a photographer shooting tight shots of a horse race, with the animal running straight into the camera, could put focus with his or her long telephoto lens right on the horse’s nose as it charges down the straightaway. But if for whatever reason that single point isn’t able to track the subject, the surrounding points instantly kick-in, lessening the chance of losing focus on the subject. But if one of the surrounding AF points is used, it will change from a tiny spot-only rectangle in the finder to a full AF point.

Accessing AF Point Expansion follows the same pattern: first, press the rear AF point select button, then press the M.Fn button. When you see a display like this, you’re in AF Point Expansion mode. Now, turn either dial, or use the Multi-controller, to move your primary AF point where you’d like it to be.

Automatic AF point selection:

Automatic AF point selection is chosen, again, by pressing the rear AF point select button and then pressing the M.Fn button (or using the Quick Control Screen) and cycling through the AF Zone selection options. The display is a bit different, depending upon if you’re pre-set to One-Shot AF or AI Servo AF. In One-Shot AF, as you toggle through the different AF area options, Automatic AF point selection is indicated by a display of only the outer, surrounding AF brackets, with no visible AF points. If you’re pre-set to AI Servo, you’ll see the same outer brackets, but with the 19 Spot AF points, and one AF point highlighted. In the area below the focus screen, where shutter speed and aperture normally appear, you’ll see a rectangle with “AF” displayed (if you see “SEL AF” in this area, you’re in one of the Manual AF point select options).

Automatic AF point selection in One-Shot AF mode: Since the first EOS camera with multiple AF points (the EOS 10s, in 1990), every Canon EOS model has allowed Automatic AF point selection. When working with non-moving subjects in the One-Shot AF mode, the EOS 7D starts with all 19 AF points active. The camera will then use the point or points which “see” the nearest subject with adequate detail. Those points will be displayed in the viewfinder, along with the round green focus confirmation light at the bottom of the display. It’s perfectly normal for more than one point to appear, if the camera detects subject matter at more than one area that’s an equal distance from the photographer.

Automatic AF point selection in AI Servo AF mode: This is where things get interesting. All previous EOS SLRs, film or digital, have required the photographer to begin tracking a subject with the center AF point when using Automatic AF point selection. Once the subject has begun to be tracked, the camera would allow the outer AF points to continue to track its movement if the subject or camera moved so that it was now off-center.

But with the EOS 7D, for the first time in a Canon EOS camera, the user can pre-select any of the 19 AF points and use that as a starting point to begin tracking his or her subject. If the subject then moves away from that point, the camera will continue to follow it. Another great new feature: if any surrounding AF points are actively tracking subject movement, once the initial AF point has “passed-off” the subject to them, these new points appear in the finder, so you always know what the camera is doing.

Once set in AI Servo AF and Automatic AF point selection, to pick a starting AF point, just press the rear AF point select button, and use either dial or the rear Multi-controller to navigate the one AF point you’ll see in the finder to where you want it to be, to initially track your moving subject.

Automatic AF point selection combined with AI Servo AF can be very useful with subjects you know will be moving, and especially if you know they will start at one area of the frame, and end up at another area.

Once again: if you see the thin outline of the outer 'brackets' in your viewfinder, you're in Automatic AF point selection mode, and the camera is going to try to select the active AF point for you.

Zone AF:

This is totally new, never possible with any previous EOS digital SLR. It’s bound to be a popular option for different types of shooting, particularly for photographers who are shooting quickly, and for moving subjects where you need a broad area of focus coverage. Most importantly, it lets the camera focus upon whatever is nearest within that area, whether you’re in One-Shot AF or shooting a moving subject in AI Servo AF.

In effect, Zone AF is Automatic AF point selection, but restricted to a small cluster of AF points in the viewfinder.

To activate Zone AF, as before, either press the rear AF point select button and then press the M.Fn button until a cluster of AF points appear in the viewfinder with curved brackets surrounding them, or alternatively press the “Q” button to call-up the Quick Control menu, and use its AF area mode option to toggle through the choices until you see two smaller brackets, and “Manual select.: Zone AF” spelled-out at the bottom of the rear LCD monitor.

Zone AF has the potential to be especially useful for action photographers, shooting subjects ranging from track and field to birds in flight. Again, it’s particularly adept at picking one nearest subject from a range of subjects, like a cluster of runners at a track meet, and putting sharpest focus on that which is nearest.

Five different zones are available: dead-center, upper- or lower-center, and left or right. As with AF point expansion, there’s no way to increase or decrease the size of a zone. You can only move it as just described. It’s also not possible to “nudge” it just a little to the left or right, for instance; only the five pre-set locations are possible. Even with these limits, this is a spectacular new option for EOS users, and a very interesting way to harness the power of Automatic AF point selection with some of the control users have previously had with Manual AF point selection.

Finally, an important distinction between Zone AF, and the previously-mentioned AF Expansion settings:

  • AF Expansion lets the user pick ANY of the 19 AF points, and the camera then uses exclusively that single AF point for focus — unless that point cannot see the subject, or unless the subject moves away from that point. In either instance, the surrounding, expanded AF points are now used to attempt to continue to focus upon the subject.
  • Zone AF lets the user pick a ZONE of 9 AF points (center zone only) or 4 AF points (any of the surrounding available zones). Automatic AF point selection occurs within this zone, with the camera using whichever AF point sees the nearest subject with detail in that zone. The photographer can pick a zone, but cannot pick one point within that zone to be a primary point, as he or she could with AF Point Expansion. As mentioned, Zone AF can be very helpful when you know you want the nearest subject among two or more to be the one focused upon. It is less useful when you want to focus precisely on one part of a subject — for instance, in a head-and-shoulders portrait, Zone AF might put the tack-sharp plane of focus on a subject’s nose, instead of his or her eye, if the camera “thinks” the nose is nearer to the photographer.

Summary:

The EOS 7D user is blessed with a spectacular new range of AF area options to choose from, and the camera can be tailored to suit a tremendous range of shooting conditions and user preferences. The AF system is certainly fast and powerful, and responsive in low-light conditions. Along with the camera’s built-in 8 fps capabilities, the EOS 7D’s AF system is a remarkable tool that will cause photographers to re-think how they shoot pictures. Many pros, for instance, who up to now have exclusively relied on manually selecting the center AF point alone, will be well-advised to learn the camera’s capabilities and experiment with moving AF points to other areas, as well as practicing with different AF Zone settings. The choices are easy to activate, and the results have the potential to be spectacular.

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