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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


I very much verify this is a serious problem.


I often find myself reverting back to my 7D.


Please find time to have a look into a fix


Thank you

Rising Star
Rising Star

Wow!  I totally didn't know this was a widespread issue and an actual technical problem; I thought it was just me and having the wrong expectations.


I will be following this thread with great interest.

Thanks please try and make this issue known, I just know people will try and hide this!

It is also documented here:


I havea  5DIII and 600ex-rt and i've noticed it does this too.


Various complaints can be found if you just google it and I believe Canon has refused to acknowledge any issue yet.

@hambergler wrote:

Various complaints can be found if you just google it and I believe Canon has refused to acknowledge any issue yet.

I hope Canon cps does acknowledge this issue soon and what determines what exact situations and camera settings trigger it, even if they are unable to do anything about the low light af problem and the af assist beam lag. The cause supposedly is that the smaller af points of the 5d3/1dx simply have trouble in these situations, the fix is the larger af point design of the 6d.


The irritation about this issue is due to the fact that obviously many people thought it's somehow their own fault (and with most other problems, it probably is) and not a potential regression in the af design in comparison to the older 5d2 or 7d/60d-like design.

I would also like to add my name to this issue.  Having come from a 40D to a 7D and now a 5D3, I can say the camera is tremendous, EXCEPT for the slow focus with assist beam.  AND I use center point as my main focus point 90% of the time and recompose.  Now, try and find that very "thin-lined" focus square in low light or against a dark object.  Very hard to do!  And when you achieve focus you shoot with a leap of faith that you guessed the focus square location correctly.  With the 40D and 7D you could see the focus square blink and didn't need the focus confirmatio dot in the viewfinder or the beep.


I would give up a whole bunch of focus squares, if I could just find the one I have selected.  Is this a light leak issue?  Just be straight with us and tell us if it can be fixed and when.


Thank you.


Hi Everyone,  

Canon would like more detailed information from you regarding these issues:


  1.  What is the focal length being used for the affected shot?  For example if the lens being used is a 24-70, what was the focal length, at the time.


  2.  How far was the subject from the camera?  


  3.  Which AF point(s) were active?

Thanks for your assistance!

Did this answer your question? Please click the Accept as Solution button so that others may find the answer as well.

1) Have the problem at all focal lengths on 24-105.
2) I find it doesn't matter
3) Single point as well as full auto


I am a wedding photographer and I started the topic over at Canon Rumors.  I find that the 70-200 f/2.8L IS II gives me the most issues with the AF assit beam.  I have shot over 20 wedding with the 5D3 and I noticed the issue right away.  The AF assist was a big help when I had the 5D2 but once it is enabled with the 5D3 it takes much longer to achieve focus.  The focus beam will flash 3 full times before focus is confirmed.  When I disable the AF assit beam and take the same picture at the same time it focuses instantly.  I don't understand why the the AF assist beam hurts the focusing performance.  Below is one of my posts from the Canon Rumors fourm the explains it a little more.  

"For me the 70-200 f/2.8L IS II without the AF assist will focus in almost an instant even in very low light as long as there is an area of some kind of contrast.  For example at wedding receptions when I am photographing the first dances as long as I can focus on where the white shirt meets the grooms neck then I am fine.  I also feel really comfortable using AI servo to track the bride and groom entering a very dark reception (so dark I may not be able to see a lot with my own eyes).  Again as long as there is some contrast where maybe the white vest meets the black jacket.  Now that is great but what if I accidentally slip off an area of contrast and my focus point hits a the dark flat area of the tux?  When that happens the lens hunts way out of focus and it takes me a few seconds to recover. In that time I may miss something I really need to get like a smile or a kiss on the cheek.  I have tried expanding the point so the surrounding areas are active as well but I found that causes a lot more hunting.  One point works the best for me.  Now when I used to shoot with the 5D2 I seem to remember being able to focus anywhere because the AF assist would work and it didn't matter if I focused on an area of contrast.  That is why I would like the AF assit to work better with the 5D3.  When I use the 5D3 the AF assit lamp will flash 3 times usually before the focus will lock and blink red.  Now most of the time it focuses much faster than the red confirmation but you really can't trust it all of the time.  I would say 90% of the time that area will be in focus before the red confirmation but it may be the time you really need that it will be slightly out of focus.  The AF assist flashing 3 full times before focus is way too long in my opinion especially since it was better than that in the past with the 5D2.  There has to be a reason and I just want to know why.  If there is a trade off because the AF points are smaller I can live with that and like I said before I have learned to work with what I have but part of me feels like I shouldn't have to."

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