5D mk III - AF microadjustment and AF-ON button issues

[eoren1]

I just got my camera back from a 'clean and check' at Canon. Had a few stubborn dust spots that I just couldn't get rid of. They also updated the firmware for me.

I took the camera and 70-200/4 IS to the beach yesterday and figured I would test out a few different AF microadjustments in the real world to see if I still needed a +3 on the tele end. Tried out 0, +3 and +5 in the field.

When I got home, I did not see the AF adjustment on the LCD info nor on the Canon ImageBrowser for any shots taken in One Shot mode; only in AI Servo.

Realized something:
I use the AF-ON button for focus.
In any mode (One shot/AI focus/AI servo), pressing and releasing the AF-On button then clicking the shutter does not engage the microAF adjustment
In any mode, pressing and HOLDING the AF-On button while clicking the shutter does engage the microAF adjustment

Can someone confirm this behavior for me? Is it specific to the 5D III??

 

[Mt Spokane Photography]

That's not the way it should work. There is a problem somewhere.

You were not using live autofocus, I assume?

 

[Loswr]

AFMA is engaged during focusing. If you've set up back button AF, and aren't holding down AF-ON, the camera is not actively focusing (which, in fact, is one of the main reasons to use back button AF). In that case, the AFMA isn't recorded in the EXIF as shown by DPP, nor is the selected/used AF point(s). So, for AFMA testing you need to either hold down the AF-ON button, or reassign AF to the shutter button (since a half-press precedes a full release, with AF on the shutter button, the camera will always be focusing when the shot is taken).

 

[ahab1372]

There was a thread a while ago about Reikan Focal in manual mode. It appears that cameras like the 1DX and 5D3 don't write into the Metadata wether AFMA was used when using back button focus and releasing the button before taking the picture, or at least they don't do it in a consistent way. They do still write the actual AFMA value into the Metadata, and they still do use AFMA. Neuro saw different information for his 1DX than I did on my 5D3.
I think it also depends on the software you use - I remember seeing a difference between different versions of GraphicConverter (which use different versions of EXIF Tool).
IIRC, there is a Exif tag AFMA ON or something like that, and it can have values like 0 (which is interpreted as OFF), 1 (ON), and 2 (UNKNOWN). In the scenario you describe, my camera wrote 2, which was interpreted as UNKNOWN, and most software seems to interpret that as OFF.

I have to go back and look at some of my shots for more details, or take some more test shots - I can let you know later today.

Bottom line is, your AFMA probably still works fine, the camera just writes inconclusive metadata when you use BBF.

 

[ahab1372]

Neuro beat me to it

 

[eoren1]

AFMA is engaged during focusing. If you've set up back button AF, and aren't holding down AF-ON, the camera is not actively focusing (which, in fact, is one of the main reasons to use back button AF). In that case, the AFMA isn't recorded in the EXIF as shown by DPP, nor is the selected/used AF point(s). So, for AFMA testing you need to either hold down the AF-ON button, or reassign AF to the shutter button (since a half-press precedes a full release, with AF on the shutter button, the camera will always be focusing when the shot is taken).

That makes sense. Thanks. I guess in One Shot, once focus is achieved, there is no use for the microAF data (it was already used during active focusing).