AUTOFOCUSING with AF-ON...is it worth it?

Started Nov 18, 2009 | Discussions thread
Anastigmat
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Re: it's another tool
In reply to John_A_G, Nov 23, 2009

I would add to your explanation the following: By using AF-on, the shutter release can be tripped any time. It is frustrating to miss the shot when using one shot and the focus won't lock and the shutter just refuses to release. Also, when using AF-ON, one can track the subject continuously and not risk accidentally releasing the shutter. That works well for birds in flight.

John_A_G wrote:

There are two reasons depending on how you set things up. Some of the settings affect how exposure readings are taken - i.e. separating exposure control from focus. But, you're talking about the separation of focus from shutter. As a sports photographer I'll tell you it is beneficial SOME TIMES but not all the time. But, it simply makes sense to keep things the same every time you shoot - so I always shoot with af-on controlling my focus. That way my hand doesn't get 'confused' at the wrong moment and forget whether my finger or thumb is controlling focus.

Here's the situations in sports where it's beneficial. Having the two separate allows you to disengage continuous focus (AI-Servo). Let's say I'm shooting baseball and I'm expecting a steal of second base (and I'm on the third base line). I can focus on the bag then take my thumb off. I can then frame my shot the way I like it - bag at the left with enough room for the shortstop to cover but also for the base runner to enter the frame. That's the peak moment I want to capture. If I track and follow the runner I could lose focus at that peak moment - I also won't get the framing right. Now, I shoot with a lens on a monopod - I can sit back and wait and not be worried about obtaining focus at the critical moment. I also don't have to keep the shutter button half-pressed to maintain focus. Now the play happens and I get the shot. But the ball is overthrown and the runner gets up and runs to third -- I can immediately start continuous focus again by putting my thumb on the af-on button. I don't have to switch between manual focus or one-shot focus and ai-servo. Similarly during non-action I can focus the shot using my single focus point and release af-on and recompose so my in-camera framing is correct. The benefit of single-shot without having to switch shooting modes which requires a button push and dial turrn.

Now, is there any benefit during action sequences in a sport like soccer or football? no. none. It's theses other instances where you want the benefit of either one-shot or focus lock without having to keep shutter half pressed where the benefits of separating focus from shutter comes out.

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