MIII - Focus Priority - New Information

Someone posted a new Canon published Mark III guide on one of the forums that talked about how different AF CF settings work, particularly for different scenarios. It is available here... http://www.pbase.com/p​hoto3nz/mark3 and the pages can be saved for printing.

The one thing that stands out to me, is the way Focus Priority works vs. how I thought it worked. I thought that Focus Priority would not take a shot if it wasn't focus locked. According to this guide, that is not true. It says that ...

1st shot:

With AF priority (C.Fn III-3-0 or C.Fn III-3-1), a fixed period of time is allotted for focusing (the lens-driving time). Focus does not need to be achieved to take the shot, but with more time to achieve focus, priority is given to achieving focus. With Shutter release priority (C.Fn III-3-2), pressing the shutter button completely will take the shot even during focusing.

This explains why you can still get OOF shots in Focus Priority.

Yes, this is not really new, some of the reviews have gone over this and even complained that there was a setting on the MkII that the III does not have.
Leaving it at the stock setting on the MkIII is a good idea,. the worst results I got was when I messed with this one.

What I did notice when I set my Mark III to focus priority for 2nd and subsequent shots is that when the camera lost focus on 2nd and subsequent shots, the fps rate dropped drastically while the camera tried to acquire focus. It still took a shot even if focus wasn't achieved but it seemed to take a longer time trying to achieve focus than the Mark II ever did, which is why the frame rate dropped.

With the Mark II, it just kept shooting whether the focus was good or not. If the Mark II did slow down to acquire focus I never noticed it.

PacAce wrote in post #3663293
What I did notice when I set my Mark III to focus priority for 2nd and subsequent shots is that when the camera lost focus on 2nd and subsequent shots, the fps rate dropped drastically while the camera tried to acquire focus. It still took a shot even if focus wasn't achieved but it seemed to take a longer time trying to achieve focus than the Mark II ever did, which is why the frame rate dropped.

With the Mark II, it just kept shooting whether the focus was good or not. If the Mark II did slow down to acquire focus I never noticed it.

Do you find that the Mark II gave you just as many or more in focus shots without slowing down (or slowing down minimally) compared to the Mark III. Along the same lines, does the Mark III slow down more and give more OOF shots?

sbressler wrote in post #3663437
Do you find that the Mark II gave you just as many or more in focus shots without slowing down (or slowing down minimally) compared to the Mark III. Along the same lines, does the Mark III slow down more and give more OOF shots?

The settings between the II/IIN and III are totally different, so comparing them is almost irrelevant. The setting that the II/IIN had... shutter priority on shot one, and focus priority on shot 2-n... doesn't exist on the III ironically.

I find that in all testing I've done, the III gets fewer OOF shots than my 4 II/IIN bodies... but maybe they were all defective. I'm starting to think that since I'm the only one that doesn't have a perfectly focussing IIN.

I have not gotten big differences in OOF when changing this setting, when tracking things running at relatively constant rates. I'm guessing the tracking is able to just stay with that. I have had some cases where the fps rate slowed way down though, and I'm pretty sure I was in focus priority when it did it. But it has been rare.

The big thing that was "new" with this info to me, was that focus priority will still fire, even if it can't focus. It just waits longer before it fires. Now think this through though... if it has lost tracking, it could actually be worse if it waits (hunting longer) than if it just fires at the fps rate. Think about it. I've always had the best results setting tracking sensitivity to fast, so that it gives up the quickest. With focus priority, I'm guessing it hasn't given up and is still trying to find what it was tracking... and it would likely move away more if you gave it more time to search... then bam... it fires at the time limit. So by my logic, you could get more OOF images with focus priority on, than with shutter priority. Just a theory.

Thanks for that link. It's a good read and I now have what I feel is a more detailed understanding of the AF CFns.

Interesting....AF micro adjustment is only for emergencies when a Canon service center is not available.

AeroSmith wrote in post #3663724
Interesting....AF micro adjustment is only for emergencies when a Canon service center is not available.

I guess this is to debunk the myth (that someone actually told me) that Canon added this feature after they couldn't get the MIII to work with lenses properly.