# 5D Mark III---AF stops working in very low light



## notapro (Jun 29, 2013)

I have a question regarding my 5D Mark III.

When focusing in very low light conditions, the AF will suddenly cease functioning, as if the camera were MF only.

What brings back AF is pointing the camera to a light source. The AF springs right into action. Still, after coming back, if focus isn't achieved farily quickly, AF will "hang" again.

Is is expected or normal for AF to stop functioning in extremely low light?

If it makes any difference, what I describe happens with the 50mm f/1.2L lens. I have not yet checked this out with other lenses.


----------



## Mt Spokane Photography (Jun 29, 2013)

Without knowing the light levels, its not possible to give a good answer your question. Any camera has a lower limit as to when it will no longer autofocus in low light. The 5D MK III is very good, but you must use the center point only when the lights go down.
Mine is able to focus down to levels where I can't capture a decent image any longer, say at ISO 25600, f/1.8, and 1/50 sec. With my 85mm f/1.8 lens.
If I'm willing to put it on a tripod, it will AF at lower levels than that, but slowly.


----------



## J.R. (Jun 29, 2013)

It is perfectly normal if you have the "Lens Drive when AF impossible" to OFF (tab AF-4). If the light is very poor, the camera will not even attempt to focus. 

This happens with almost every lens that I own if I try shooting in extremely low light situations.


----------



## notapro (Jun 29, 2013)

JR,

I checked the settings, and for "tab AF-4", the selection is "ON".

What you say is exactly what I experience: the camera does not even attempt to focus.

______________

However, with the 24mm f/1.4L II, I seem to be unable to replicate the "issue".

I'm shooting into an almost completely dark closet, ISO 100, f/1.4, 1/60 in order to get the AF to stop working (for diagnostic purposes/to see if I can replicate the issue).

In actual/normal use, I came across this problem when shooting an evening shot (with the 50L). The lens drive just stopped. It had never happened before, so I got curious about it. I switch to MF when necessary, but had never come across the sudden "hang" of the AF lens drive.


----------



## notapro (Jun 29, 2013)

Just a follow-up here.

What I describe happens so far may be the case for only the 50L and 5DIII, as the same lens on a T3i has the camera attempting continously to AF even in almost complete darkness.


----------



## J.R. (Jun 29, 2013)

notapro said:


> JR,
> 
> I checked the settings, and for "tab AF-4", the selection is "ON".



It should not happen in such a case and the focus should hunt at the very least (my settings are "OFF" so I experience this often enough when it is getting very dark).


----------



## J.R. (Jun 29, 2013)

notapro said:


> Just a follow-up here.
> 
> What I describe happens so far may be the case for only the 50L and 5DIII, as the same lens on a T3i has the camera attempting continously to AF even in almost complete darkness.



Are you using the same AF modes on both the 5D3 and the T3i?


----------



## notapro (Jun 29, 2013)

In response to JR, yes, the same AF mode is used, though I have more information now.

With the 24mm and 50mm lenses attached and in complete darkness (or with lens caps attached), the T3i lens drive will continue to function every time I press the shutter.

On the 5D Mark III with the 24mm lens, the lens drive will continue to function as well in complete darkness or with the lens cap attached.

With these two cameras and these two lenses, then, it is only the 5D and 50mm combination that'll get the AF lens drive to stop. I'll press the shutter release button with no effect, as if the camera is turned off. I would guess that this matter is related to the specific camera-lens combination and does not likely indicate any sort of "fix" or resolution is necessary. Who can say . . .


----------



## dgatwood (Jun 30, 2013)

notapro said:


> With these two cameras and these two lenses, then, it is only the 5D and 50mm combination that'll get the AF lens drive to stop. I'll press the shutter release button with no effect, as if the camera is turned off. I would guess that this matter is related to the specific camera-lens combination and does not likely indicate any sort of "fix" or resolution is necessary. Who can say . . .



There's an Amazon review from a 5D Mark II owner that had the same problem with the 50mm f/1.2 lens. Sounds like a firmware bug to me.


----------



## notapro (Jun 30, 2013)

The problem seems to have resolved itself now, as inexplicably as it "appeared".

Maybe it was the phase of the moon, the weather, maybe this problem is intermittent, . . . who knows.

Just posting here to say that all's well again.


----------



## dgatwood (Jul 1, 2013)

notapro said:


> The problem seems to have resolved itself now, as inexplicably as it "appeared".
> 
> Maybe it was the phase of the moon, the weather, maybe this problem is intermittent, . . . who knows.
> 
> Just posting here to say that all's well again.



Dirty contacts.


----------

