Reading the 7D/5D III manual in the section where you can assign different functions to different buttons, one thing that stumps me is the AF off function. The manual says, by pressing and holding the button assigned to AF off, you can lock the focus during AI focus. Ok, but how is this different from just releasing the assigned AF button. I have always assumed if I lift my finger from the AF button AF stops in servo. Is this not true and if it is true, why would you need the AF off function?
Ok, I see that, but why do you need this function if you can just lift your finger from the AF button anyway. This function allows you to use a button on the camera rather than the AF stop button only found near the front of supertele lenses.
Some people like to keep AF on the shutter button. Then you can use the AF-off to prevent the camera from focusing or refocusing when pressing the trigger.
gfiksel wrote:
Some people like to keep AF on the shutter button. Then you can use the AF-off to prevent the camera from focusing or refocusing when pressing the trigger.
Ok, I see, so if you are someone that uses the * or AF On button for AF, then the AF stop function is not necessary.
I like half press for focus, I have a good feel for it on my 7d. I use AF stop under my thumb to recompose without moving my focus point. For me, since I use center point 99.9 percent of the time, it is quick and easy to simply push the AF stop after getting my focus plane set.
Also works very well when shooting through the net for volleyball, for example. Set the focus before the play, then hold AF stop so you don't lose the player because of the net or a crossing player.
gfiksel wrote:
Some people like to keep AF on the shutter button. Then you can use the AF-off to prevent the camera from focusing or refocusing when pressing the trigger.
Yep, I'm one of those people. I tried, but never took to using "back button focusing". So I do have AF-off assigned to my AF-on button on my 7D and focus with the shutter-release.
In some past discussion, some back-button-focusing devotees have tried to convince me of the superiority of their method over mine, but either I'm dense and just don't get it, or perhaps it is actually just a matter of preference and either way works fine. Perhaps depending on the nature of the shooting, one or the other method makes more sense.
Top or back focus is of personal preference. Some say the camera is held more steady upon shutter release with back AFon.
However, I took the OP's original question really to be what is AF Off used for? Besides the above example, think of any scene that has you tracking with AI Servo a specific subject. Using AFoff helps you prevent the camera from switching focus to a new distracting subject should the one you want be obscured by some other object or thing. Think sports, think birds, think kids, etc.
Back button AF off is superior in one case to back button AF on. You can leave the half press AF start on the shutter...
You might wonder why this is a bonus but when you hand your camera over to your brother or SO or some complete random stranger they won't give you that puzzled look when the camera won't auto focus.
tonywong88 wrote:
You might wonder why this is a bonus but when you hand your camera over to your brother or SO or some complete random stranger they won't give you that puzzled look when the camera won't auto focus.
All my siblings use back button focus. It took me a while to convince.
It took me a while to convince.