Predictable, Not Particular
When autofocus can let you down
Pictured above is the earliest camera model with which I began my work: the venerable Pentax MX. The times have since changed. When rebooting in digital, I felt a little strange adjusting, particularly with respect to the viewfinder. When I picked up the white Pentax K-r as my first digital SLR, I had to relearn the basics. With a tighter field of view, a viewfinder covered in metadata rather than a light meter, and an autofocus system, the digital K-r was a big change.
With time, I had figured out what was bothering me. Instead of doing the split image manual focus in the center of the frame like many film-era bodies including the MX, I found my K-r being very responsive with its autofocus. It was perhaps even unwieldy as a little AF unpredictability caused me a lot of concern.
While some appreciate the jackrabbit AF systems of modern cameras, I did not. Parsing through the manual, I found what might have been the setting to make me feel back at home: autofocus point adjustment. I could choose from an 11-point auto mode, 5-point center cluster, or center-only, which is what I desired. Changing to center AF was such a massive improvement to how I use the camera, that it was among the first things I had done with my encore, the K-5IIs.
While camera manufacturers continue to "wow" us with autofocus that attempts to register depth, follow a subject during a burst, or continue during video, they also seem to have given AF a little too much caffeine as the many AF points can often lock on to incorrect or undesired subjects. Perhaps this happens only once out of a hundred times, but in my book maybe this is once too often.
I chose to have more control over my camera by wrestling some responsibilities away from it. We do this for exposure all the time, but rarely for AF. By switching the autofocus mode from auto to single-point, I found myself to be missing the subject less frequently and almost never missing the shot itself.
“Try this at home! You can be just like me!" I may insist were I a lesser writer. Different cameras have different menu systems, but one way or another, your DSLR will allow you to change the AF mode. On the following image of the tireless K-5, Nirvana is a simple hardware switch away.
The AF point selector on a Pentax K-5
Roll the switch and let the shutter loose.
Setting the camera's autofocus to the center point can be liberating, even when dealing with a more capable body like the Nikon D7100 or Pentax K-5IIs. A fleeting movement in street photography can be quickly and confidently captured because we know exactly where to place the subject in the frame, saving precious time.
We may have to recompose, and yes I understand that in doing so, the critical sharpness may move an inch as we readjust the camera. This is where individuals can figure and adjust to their own tastes.
Typically I shoot with the DA* line of Pentax lenses. They happen to have the touted Supersonic Drive Motor (SDM) which is known for being quiet, but not that fast. By knowing where the subject is going to start, every single time, I tend to shoot a little faster to compensate comfortably for the slower AF speed.
A colleague of mine objected when I introduced center AF to her, insisting that I should simply choose an AF point out of the array rather than sticking to the one in the center. AF point selection is a handy feature for when you are on a tight tripod or an AF point happens to land exactly where you want it to be, or perhaps if you have forgotten about manual focus.
Whilst out and about, taking your eyes off the subject (or away from the viewfinder) to choose the AF point from the array costs precious time, especially with fleeting subjects. By the time the photographer looks back down range, one could have taken several shots.
It isn't that I am saying autofocus isn't useful, as it most certainly is. It isn't even that I am saying center point is the only other option. It's not. It's just that feeling of disappointment when eager AF finds a different subject than the one you had in mind.
Perhaps it may be time for you to test this out. Or if you have, perhaps to reevaluate. Regardless, I'll be here in the comments if you feel I am wrong.