Saturday, January 9, 2010


I’m learning to use the AF-ON button on my 7D. Well, perhaps learning to use is not quite the best wording. AF-ON is, after all, just a button. I can already press it but I’m not in the habit of doing so. My habit is to press the shutter release button halfway, hesitate and then complete the press.

To take a picture, you point the camera at the subject and press the button – right? George Eastman built his company around the motto “You press the button, we do the rest”. More recent is the ongoing joke slogan about PHD cameras (“Push Here Dummy”).

The shutter button on many (most?) modern cameras actually has two “stopping points” or triggering positions. The first position is about halfway down. You can feel this first position by pressing the shutter button lightly and slowly. With a little practice, you can quickly get a feel for the effort and distance and the half-pressed button then comes quickly and naturally. The second position is the actual stopping point and is at the bottom of the shutter button stroke or press. The half-press has been my habit for a long time. It was especially useful with the G3 and G9 because those cameras had a very noticeable shutter lag unless the half-press technique was used. In addition to reducing shutter lag, the half-press was especially useful in the “focus, recompose, shoot” technique that I almost always use.

In addition to the two position shutter button, the 7D also has the AF-ON button. This button acts like the half-pressed shutter button. So what? Why use AF-ON ?

In addition to focusing, the AF-ON button locks focus as long as the button is held down. This means that I can focus, recompose, shoot, recompose, shoot, shoot, shoot, recompose, shoot, etc., etc. There’s no need to refocus as long as I remember to hold down the button. This is especially useful in portrait shooting. I’m no longer waving the camera around as I continually focus, recompose and shoot.

A good feature, AF-ON .


Миша said...

I honestly never thought of that, good point!

DBump said...

That is an exceptional button--I'd never noticed it in poring over reviews of it. Thank you!
On my aging rebel, I've gotten in the habit of doing something related. I've changed the Shutter/AE lock Custom Function (IV-10, on my camera) to AE/AF, no AE lock, which, despite the confusing descriptions in the manual, simply removes the focus control from the half-press shutter (which now only causes the camera to meter) and instead moves it to the * button (replacing AE lock). There's a brief and awkward learning curve, but it really is quite brief. Now I center over what I want to focus on, tap * to focus, center over what I want to meter on (if needed), half-press shutter to meter, and finally recompose for framing, and full-press the shutter. For multiple shots, you don't have to hold anything down--just tap * once, release, and shutter away until you need to change focus. Very useful for eliminating even the fast focus lag of a DSLR--for macro or high speed, it's a shot-saver.
I'd love to have an AF-ON button too.
Great blog--thanks for all the good info!