EOS R6 Mark II requires multiple shutter presses to focus in low light

[LifelessLewis]

Hey, I have a Canon R6 Mark ii with an RF 24-105 L f/4. I am using spot autofocus with no tracking in one shot mode. Sometimes in low lighting it will fail focus on something with slightly low contrast. However, if I half press the shutter a few more times it will eventually focus, showing that it can manage it at the point I'm trying to focus on.

I have ensured that the Lens drive when AF impossible is set to continue focus search. However it's like it doesn't actually search the full focus range to even try, just decides that it can't focus without actually trying. Is there a way to force it to search the full focus range before deciding that it's out of focus?

Thanks.

[deebatman316]

Your camera is working correctly DSLRs work the same way. If the AF system is way out of focus it will never get close this is even true with DSLRs. The camera focuses wide open so the depth of field always stays the same.

[deebatman316]

If its all the same color the camera won't lock focus. The camera needs contrast to focus there isn't contrast.

[p4pictures]

The AF system needs contrast to work. Low contrast subjects in low light are most challenging for AF. Dual pixel AF has left / right photo diodes in each pixel, these work best with vertical lines of contrast. 

If you are handholding the camera it is possible that each time you press the shutter again you move a fraction and the camera then finds enough contrast to focus on. I found that if I aim at a blank painted wall the camera mostly fails to focus and the AF point shows in red. If I move slightly so that more contrast is found the camera focuses as expected. If the lens is focused manually to be very out of focus then it is hard for the camera to find any contrast to focus with, and the AF point goes red. 

The lens drive when AF impossible is more useful when using servo AF. Here if the subject is lost the lens stops or continues to search as expected. Using ONE SHOT AF is literally one shot, if the focus is not found then the camera stops looking. You may find that SERVO AF is actually better at trying to continually focus. 

I note that you said no tracking was used, does this mean you set the subject to detect to none, and switched off Whole Area Tracking Servo AF? The latter setting only applies when SERVO AF is used, not ONE SHOT. 

[LifelessLewis]

So, yes I am handholding it, so I suppose micro movements mean i might end up pointing at an area with slightly more contrast. The wood grain I'm trying to focus on is running vertically.

Yes tracking was off (although i know most of those settings are irrelevant for one shot). However I did also try in SERVO AF and it still stopped trying to achieve focus. Until i engaged the af a few more times then it eventually would.

[Waddizzle]

Be cognizant of the lens’ MFD, minimum focus distance.  This specification describes the minimum distance to the subject.  Move closer than the MFD and the lens will fail to focus.  

[EDIT]
The MFD spec only applies to the shortest focal length for a zoom lens.  As you zoom out to longer focal lengths, the MFD will increase by a significant amount.

[LifelessLewis]

Yeah the thing I'm trying to focus on is about 3-4 meters away, definitely not something as simple as that haha.