Rudy Winston
Rudy Winston

Rudy Winston has over 17 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.

An inside look at Spot AF

December 08, 2014

Since its introduction in the original EOS 7D back in 2009, most high-end Canon EOS DSLRs have offered the ability to reduce the size of an AF point. Spot AF, as it’s called, reduces the size of the AF sampling area at the AF sensor and means that AF can be performed on a more isolated part of a subject or scene. Examples of this might include being able to focus right on the eye that’s closest to the camera in a tight portrait, or on a small drop of water or dew on a flower in a macro shot.

We’ll explore this useful focus option in this article, highlighting strong points like those listed above, as well as its limits and when it may not be the optimal choice.

Canon EOS models offering Spot AF

Spot AF is not universal across the Canon EOS line-up. Again, it was first seen in the original EOS 7D (introduced in late 2009). As of late 2014, here are the models with this AF Area option:

  • EOS 7D
  • EOS 7D Mark II
  • EOS 5D Mark III
  • EOS-1D Mark IV (note: possible only via Custom Function, when AF Stop button on a compatible EF super-tele lens was depressed)
  • EOS-1D X

With the exception of the EOS-1D Mark IV (as noted above), Spot AF is accessed by cycling through the AF Area options on your camera. It’s indicated by a “box within a box” icon, seen in the viewfinder at the location of whichever AF point is active at the moment. Spot AF always uses a single AF point; there’s no way to group multiple AF points and have their sampling areas individually reduced in size.

So what coverage does Spot AF actually provide?

First off, the display on your camera’s focus screen with the familiar “box within a box” is a little misleading… Spot AF doesn’t cover the area of the smaller box that’s within the normal AF point.

In actual fact, the two illustrations below are a close approximation of what’s actually covered by your camera’s AF system. You obviously don’t see the cross-type focus coverage of the AF line sensors in the viewfinder, but this gives you a good idea of what’s actually covered. (This illustrates how the EOS-1D X covers standard Single-point AF and Spot AF; other EOS cameras with Spot AF are very similar). As you can see, two things immediately become apparent:

  • Standard, Single-point AF provides coverage that extends BEYOND the borders of the AF point you see in the viewfinder
  • Spot AF actually covers an area virtually the same size as the primary, single AF point you see in the viewfinder… it definitely extends beyond the inner “box” you see when Spot AF is indicated on your focus screen

Single-point AF — actual AF area covered


 

Spot AF — actual area covered

 

So it’s clear that Spot AF definitely samples a smaller area of any subject you aim it at, even though it’s not as confined as the viewfinder icon may have led you to think. Even so, understanding this gives you insight into how to effectively use this feature.

Using Spot AF effectively

Again, the real benefit of Spot AF in a Canon EOS DSLR is its ability to focus upon smaller parts of your subject or scene. In situations where the photographer has time to carefully point the active AF point at a single, precise area of a subject, this can mean that actual AF is often more likely to be at the exact plane that the photographer desired. We illustrated a couple of typical examples (above) with a portrait and macro shot.

It’s important to mention here that Spot AF is always at a single, manually selected location within your AF system’s AF array. You can use the center AF point or move to any other point that can be manually selected and change it with the camera’s AF Area commands to Spot AF (and any manually selected AF point can also be expanded, with Canon’s AF Point Expansion… achieving the opposite of what Spot AF offers).

Another example of where Spot AF’s more limited coverage might be an advantage is when trying to focus a lens through an opening in a foreground object. In cases like these, Spot AF’s narrower coverage makes it less likely to accidentally pick up a bit of that foreground obstruction and, instead, focus on that of an actual subject.

Really, any time you have a stationary or slow moving subject and want to be more precise about where on that subject you place sharpest focus, Spot AF is an option to keep in mind.

“Precise” is not the same as “accurate!”

We’ve said several times in this article that the Spot AF option does let you focus on a smaller area of your subject. In doing so, it does allow you to place focus with more care and precision — at least in some instances — than standard, Single-point AF would. But it’s vital for Canon EOS users to understand that Spot AF is not inherently more “accurate” than normal Single-point AF would be. If you set up a test, photographing a flat chart or wall with a tripod-mounted camera shooting squarely into it, you’d get equivalent results in terms of focus “accuracy” in test shots taken with Spot AF vs. the larger Single-point AF. So if you simply switch to Spot AF for all your shooting and expect that you’ll get a higher percentage of sharp images, you’re going to be disappointed.

The difference is that Spot AF will indeed let the photographer place focus upon a smaller area of a subject. And in doing so, again, focus can be more precisely placed — when circumstances and time allow the shooter to accomplish that.

Because of this, there are situations where Spot AF is probably not the right AF Area option to be using. These can include:

  • Photographing moving subjects
    Sampling a smaller area of the subject, the AF system is able to view even less subject detail, contrast and texture, especially if shooting multiple frames in a fast sequence. In many instances with moving subjects, in fact, doing the opposite (expanding the size of an AF point with either AF Point Expansion or Zone AF) can deliver more consistently sharp frames. In general, as a rule of thumb, Canon does not recommend Spot AF for most situations where AI Servo AF is being used to focus-track a moving subject.

 

Spot AF’s small AF coverage means it may pick up only plain, solid areas of a moving subject, like this skateboarder, and deliver inconsistent sharpness during a sequence of shots with AI Servo AF.


 

  • Subjects that are hard to keep a small, single AF point upon
    Sometimes, a subject may not be moving toward or away from the camera and, yet, it may be difficult to keep a small Spot AF point upon one part of that subject. Anything from an animated speaker at a podium to a small bird on the branch of a tree may benefit from focusing upon a wider area of the subject, using standard Single-point AF or even one of the AF Expansion or Zone AF Area options.

    This can extend to situations where steadily hand-holding a lens may be difficult, causing the active AF point to move around a subject… an example might be trying to photograph with a hand-held or monopod-mounted telephoto lens.

  • Subjects that have little detail or are in dimly-lit conditions
    AF systems thrive when the AF point can see significant contrast or detail of the subject. In situations where this is reduced or lacking, the broader coverage of standard Single-point AF gives the AF system more potential information to work with and sometimes can be the difference between a sharp first frame versus struggling to get the sharpness you want.
Summary

While it’s not necessarily the go-to AF Area setting for every situation, Spot AF gives the experienced DSLR shooter a means to work even more carefully with his or her AF and place the sharpest focus even more precisely on the subject where it’s wanted. If you own a camera with this feature, it’s worth experimenting with and learning where it can be of benefit to you. Simply keeping in mind the actual area covered (see the graphics, above, in this article) goes a long way toward truly maximizing Spot AF’s potential. And, equally important, is awareness of where the other AF Area options display their benefits.

Another instance where focus was carefully placed, this time on the leading edge of a flower’s detail. And, this is another instance where Spot AF could be helpful in putting focus exactly where the shooter wants it.

 

The beauty of Canon’s advanced AF systems in today’s mid-range and high-end DSLRs is the flexibility and control they offer. AF Area, or the size of an AF point, is easy to change on-the-fly with the camera still at your eye. No one system or set-up is perfect for all situations, but Spot AF is one of those tools — even if you think of it as a specialty tool for limited situations — that can be invaluable when one of those situations comes up.

The CDLC contributors are compensated spokespersons and actual users of the Canon products that they promote.

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