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5D3 + AF assist beam = slower focus


Hello All,


While I am new on these forums I have been on the Canon Rumors Forums for a few years now, 


I really wanted to bring this too the attention of you and Canon as it is simply a highly important problem, those of you that don't know, the 5D3 suffers serious focus locking issues when a Canon speedite is attached in Low light, the AF assist beam causes lag with the AF from the 5D3, this makes it virtually impossible to achieve focus in low light when the speedlite is attached, I wanted to bring the topic to this forum, so I have pasted a link to all the discussion we have already had about this problem at Canon - see below



Please help in letting Canon know this is a very serious problem and effects the cameras performance in most working environments when a speedlite is attached and working in low light, conferences, nightclub work, weddings etc, and can stop the photographer completing the job or task.




180 REPLIES 180


Will someone who gets a 6D please post your view on whether this issue is present in that camera as well?  I might just buy a 6D, but this would be a big deal to me.  Thanks!


Canon 5d mk 4, Canon 6D, EF 70-200mm L f/2.8 IS mk2; EF 16-35 f/2.8 L mk. III; Sigma 35mm f/1.4 "Art" EF 100mm f/2.8L Macro; EF 85mm f/1.8; EF 1.4x extender mk. 3; EF 24-105 f/4 L; EF-S 17-55mm f/2.8 IS; 3x Phottix Mitros+ speedlites

Why do so many people say "FER-tographer"? Do they take "fertographs"?


I finally had a chance to compare both my bodies (5D3 and T1i) with two flashes (600EX and 430EX II).  I used the 40mm f2.8 for both (at first) with center point selected to keep things as consistent as possible. I shot into my walk-in closet, so it was dark enough to trigger the AF Assist light but with the door open so some ambient light would trickle in.  I turn the focus confirmation beep back on to have another indicator of when the camera thought it was focused and when it fired. I tried both camera with both flashes.  I did not time anything with a watch because if it's close enough not to be able to tell the is a significant difference, I really would not be bother which one is technically faster. That said, here are my observations:

5D3--regardless which flash used, the body had the marked hesitation that I mentioned earlier. This is not just a little shutter lag--this is a full second or two, the moment is gone, I didn't get anything and, if I did, it is not in focus.  This is beyond annoying, this is failure when mission critical.  There was no perceptibly meaningful difference between the flashes, so this lead me to believe it's the way the body acquires focus.  I noted the two or three step confirmation process someone noted earlier. This was the behavior no matter which focus point or AF method was selected (excluding SERVO).

T1i--press, shoot.  find another spot, press, shoot.  repeat, repeat.  All in focus, all virtually instantaneous and at worse considerably better than the best attempts with 5D3.  If anything, 600EX performed better than 430 EX II (thank goodness for that) on this body. This is what I was expecting from the 5D3 and it's not even close.  (I repeated the test with my 15-85mm zoom and the results were consistent regardless of the focal length and aperture setting). 

I'm now even more convinced it's a serious with the 5D3 and not the flash.  There is no way my T1i (which I still love) could/should outperform the 5D3 under these circumstances, especially given the type of photography the 5D3 is geared toward.

Canon!.......this is not going to go away....please reply ASAP!

At this point I am also convinced it is the 5D3 not the 600 that is the issue. I also think I have not been duped. Aside from my 5D3 struggling with the AF assist beam it takes very consistant images even using the outside AF points.



I agree the camera has its strong points and focuses very well in Good light...but for events in medium and low

light...which is what most wedding photogs is totally useless. I got along fine with my mark 2 up til

now...I was hoping for more , not less performance.

echelonphoto  can you clarify whether or not the disapointment is during ALL low-light situations (flash or no flash) or only those where AF depends on the assist beam from the flash?

I have found that it doesn't make much difference whether you use the AF beam or not. In one shot mode...its just

ai servo seems faster...but its hard to trust it because you are not seeing where its actually focusing in the frame

then we have two issues to deal with


1.  low light no-flash  - verifying this will require carefully controlled, specific EV valued tests between different cameras, using repeatable targets


1.  low (and "no") light with the assist beam.  this should be near trivial to reproduce -- just go into a closet and close the door. 

I actually don't know if this is the 5DM3's problem, because I'm having the same issue with my T3I and 430 EX ii(see my topic in speedlight forum). Please Canon, fix this problem!

I'm an advanced amateur, am not the average point-and-shoot photographer out there, and am willing to take any critique or advice that will improve my photography.

If you have a handly link, we'd be happy to compare, but let's not muddy the water here.  This IS a 5D3-specific issue and not a speedlight issue.  I'm not saying your T3i does not have an issue or that your 430EX II doesn't have an issue, but clarity is important if Canon is going to address this problem. 


Since the T3i has the same DIGIC processor and AF system as the T1i (and I've set a baseline for performance with the T1i and the 430EX II), I am not sure we are talking about the same thing.