How do you track a subject with a DSLR?

Started Jul 24, 2013 | Discussions thread
Eamon Hickey
Veteran MemberPosts: 3,170
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terminology: "tracking" has two meanings
In reply to mpgxsvcd, Jul 24, 2013

The biggest issue in your question is that people often use the same term "focus tracking", when they are actually talking about two different things (and the camera companies don't have standardized terms for these things).

One meaning of "focus tracking" is the task of following a subject whose position is changing within the viewfinder. This is what Olympus and Panasonic (and others) call focus tracking. The subject changing position within the viewfinder could be caused by the subject itself actually moving but it could equally be caused by the photographer moving the camera (and in this case the proper focus distance doesn't actually change -- i.e. the lens should not change its focus position.)

A different meaning of "focus tracking" is the task of following a subject whose position is actually changing in the real world -- i.e. it's moving. If the subject is moving toward or away from the camera, the lens must change its focus position to keep the subject in focus (and the subject's position in the viewfinder may not change at all, if the photographer moves the camera in synchronization with the subject. You can keep a running dog in the center of your viewfinder by panning the camera with him.) Another term for this task is "follow focusing", and it may be a better term. This is the task that Continuous AF (C-AF) is designed to perform.

DSLRs (with phase-detect AF) are better at the second task -- follow focusing. They aren't necessarily any better at the first task.

mpgxsvcd wrote:

Everyone keeps saying that DSLRs track for AF much better than any mirrorless camera. However, I often wonder how you tell the camera what to focus on when you are not using live view with a DSLR. If the subject moves around the screen how do you tell it what the subject is?

Also what if there are multiple subjects? How do you tell the DSLR to ignore one of the subjects and only follow the other subject?

These are two of the huge challenges of autofocus (in DSLRs and all other cameras). They have been responsible for probably hundreds of millions of missed shots. It's true that you can sometimes -- not always -- overcome them more easily with a Live View camera with a touch screen if you have the time to touch the screen between shots (for sports you would not normally have that time). (Also note that you can specify a particular focus patch in nearly every DSLR, so if you know your subject will be on the right side of the frame, you can pick a right side focus patch. It's not harder than doing something similar on a Live View camera.)

All the camera companies have developed automatic algorithms for trying to overcome these problems -- obviously, the algorithms for DSLRs are based on much different inputs because they don't have a Live View to work with. But this is one of the reasons why Canon and Nikon completely dominated the DSLR market and why they command 95% or more of the sports photography market -- they both spent tens of millions of dollars on R&D over the last 20 years trying to solve the problems you highlighted for phase-detect SLR cameras, and nobody else did. So when the digital boom came along, nobody else could match their AF technologies.

Just as one example, Nikon developed in the mid-1990s a feature they call "Focus-tracking with Lock-On". It's designed to ignore momentary obstacles that flash between the camera and the subject when the camera is follow focusing. The classic case would be a referee (umpire) crossing between the Sports Illustrated photographer and the soccer player he's follow-focusing. The "Lock-on" algorithm is supposed to ignore the referee, even though he momentarily occupies the focus patch, and keep the lens focused on the more distant soccer player.

Canon, of course, has similar capabilities. In both companies' pro cameras, the way these algorithms operate -- the refocus delay etc. -- can be adjusted by the user.

More and more now I am starting to think that the whole AF tracking issue with mirrorless is just a stereotype that has progressed through the ages.

Nope. For meaning #2 -- follow focusing of moving subjects -- DSLRs are still far superior, with the exception of the Nikon 1-series CSCs, which use on-sensor phase detect AF. I've used three top CSC models from Sony and Olympus (including right now the E-P5) so far this year, and they still trail DSLRs by a wide margin for follow-focusing action. I test this carefully because, although I don't shoot sports very often myself, I'm interested in the technology question. Eventually, CSCs will catch up, but right now, they can't compete effectively (especially against the top pro DSLRs) on this one particular issue.

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