Canon 7D Auto Focus
I’m often asked to compare the auto focus systems of the different cameras that I use and have used. When I compare the auto focus system of my Canon 7D to that of my Canon 1D Mark IV, I have no question that the auto focus system of the 1D Mark IV is better than that of the 7D, but I truly believe that the differences in the capabilities of the two auto focus systems are not nearly as great as one might be led to believe from reading posts on internet forums. And, even though I know that the 1D Mark IV auto focus system is better than the one on the 7D, my in-focus shot rates with the two cameras are so close as to be virtually the same. That is, I think, because I came to realize some time ago that the differences in the auto focus systems of various cameras are not nearly as important as is using them with solid technique. Below, I will briefly discuss some of the factors that help me to get the most out of the 7D auto focus system.
First, my shooting style is generally quite deliberate. I try to anticipate action and to be ready to shoot. When the opportunity to shoot comes forth, before I click the shutter button for the first time, I make sure that I have properly locked the selected auto focus point(s) onto the subject. When I start shooting, I try to be very aware of what is happening, and, as soon as I start to sense that I am losing contact between the selected auto focus points and the subject, I back off of the shutter and make sure that I have, once again, properly locked in focus with the selected auto focus points before I start shooting again. I also, instead of shooting long continuous bursts, try to shoot in shorter bursts, and doing so allows me to be continually bumping the auto focus so that I will be sure to be locked on the subject when I need to capture the action that I want to capture.
Most often, it is my preference to shoot with the center focus point expanded to surrounding points. Doing so allows me some room for error with regard to maintaining contact between the subject and the active auto focus points, but it does not give the camera as much latitude to have to “guess” what the intended subject is as I would be giving the camera by using auto selection from all focus points. In general, I have more confidence in my ability to keep the focus point on the subject than I have confidence in the camera being able to guess as to the subject on which I want to focus, and this is my thinking regardless of what camera I am using and regardless of how sophisticated its auto focus system is. With the 7D and with other cameras that I have used, the vast majority of times when I get out-of-focus shots, the cause is my failure either to properly lock in initial focus or to maintain contact between the focus point(s) and the subject.
Auto Focus Custom Functions
With all cameras that I have used, it has been my thinking that custom function defaults are the defaults for a reason, and that reason is that they are the settings that should work the best in most situations. With the 7D, I use the default auto focus custom function settings for virtually all of my shooting. If I do occasionally change a setting away from the default, it is only if I have a specific purpose in mind and if I am confident that I know that changing a setting is going to help me to achieve that purpose. I have come to believe that there are many who actually end up diminishing the auto focus capabilities of their cameras by changing auto focus custom functions in a somewhat random manner and without real purpose.
Use of Micro Adjustment
Similar to my thinking about auto focus custom functions, I have also come to believe that there are many who have diminished the auto focus capabilities of their cameras by doing careless and/or haphazard micro adjustment. I believe that micro adjustment can be a very useful tool, but I only use it (a) if I have some reason, confirmed with careful testing, to believe that an adjustment is actually needed and (b) if I have taken the time and care to do an accurate micro adjustment. When I do micro adjustment, I make sure that I have set up the camera and target at appropriate distances with the camera sensor plane and the flat target perfectly parallel to each other and at the same height. I make sure that the camera is firmly locked onto a solid tripod, and I make use of a cable release or remote live view shooting to insure that camera shake is reduced to an absolute minimum. When I have reached what I think is the correct micro adjustment, I repeat the procedure at least 3 or 4 or more times until I am confident that my results are accurate and consistent. And I would never even consider trying to do micro adjustment in the field. Trying to do so can yield a very inaccurate result if there is even slight camera movement or if the sensor plane and the plane of the target are even a bit off from being perfectly parallel to each other.
Most of what I have explained above is, I think, little more than common sense, but it is using that common sense that has allowed me, I think, to have a very high success rate with the 7D auto focus.