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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 find I have the problem with the 3 lenses I have, I own a 24.1.4 II and a 50.1.4 and a 70-200 I L 2.8 and all lenses caursed the 5D3 to almost "hang" like it was just not doing anything, you can imagine witnessing this for the first time you start to sweat, " like whao what the hell is happening"  I have just now tested the 5D3 with the 430EXII and can see that when I focus on anything that is darker, a black Bag etc, a darker toned object the 5d3 will only focus when the 430EXII has beamed atleast 3 times, I do believe the problem is not only with the 430EXII but with all other Canonspeedlites, 

I can imagine from other people stating its worse with the 70-200 is because at lengh the beam is also weaker, when I first noticed the problem I was doing work at no more than 6 feet away.


It makes me think that the 2 units are not in sync with each other when in darker situations,

I would also like to add, i used Centre Point AF, then tried to use expanded points, nothing helped,

same here on 5D3 with these lenses: 70-200 f2.8L II, 24-70 2.8L II, 35L, 50 1.4

happens occasionally with all lenses with 580EX II and 600EX RT. 

For me it is always a low-light wedding reception. i'm usually 2-5 meters away from subjects. 

i do have my shutter release priority to Focus.

when this happens, it is pretty embarassing.


waiting for the "oh, wow that takes long to focus... what kind of camera is that?" 


hope this can be fixed soon!

Small sample size, but I definitely experienced this as well on a job. (5d3+580EXII)

I thought it was a personal learning curve situation at the time, but focus would hunt for 2, 3, 4 seconds and often not ever find a solution.

I was using primarily the 70-200mm f/2.8L IS II at all focal lengths

Subjects were anywhere from 10 feet to 40 feet away

Mostly Spot AF, and I believe occaisionally AF Expansion - 8 additional

Thank you. 

Problem is always present in near dark environments (nightclubs, dark wedding receptions), usually shooting people and the scene. AF Assist beam ON with the 580EXII and the 600EX


1. I primarily use the 24-70 L II. The problem arises above the 35mm range, very often at 70mm.

2. Distance to the subject is between 1 to 2 meters. The more the distance the more lag.

3. I always use Single Point AF at the center. Outer edges are noticable more lagging.


Mode : M

shutter: varieing betweeen 0.8-1/100 seconds, depending on the situation

F-number: 2.8-4.5


ISO 800-2500

One Shot AF

Evalutative meting


Jusy going to follow.  

So I put my new 70-200 2.8 II on my 5D3 and tried out 600EX-RT and tried it out in a very dark room. Like Jaayres20 stated at times it would blink 3 times before AF lock. Other times was almost instant. Room was so dark it did not work at all without it.




1. Wiggle room. The flash has a bit of play in the shoe.  At 15 -20 feet if you move the flash to the left and then to the right there is a significant difference of where the vertical beams line up as compared to the center focus point.


2. The vertical beams are pretty wide at 15 - 20 feet.  


3. It seems the AF assist is a bit weak in illumination for that distance but I'm not sure.  I sold my 580's so I can't compare.


Seems to me the grid patterns in my 600 and not not sure about other flashes are not fine enough. Is the focus point being completely within strip of AF assist light (or not) causing this at times? I imagine that the whole idea of the patterns is to create contrast at the target. If the focus point is completely within the red strip does it still work? I'm not an engineer but my thought is somewhat, however weak illumination would be a hinderance as well. 


I used to own a 5D2, 70-200 F4 IS and 580EX II and I don't recall this amount of lag. I have yet to field test the new gear. It is not horrible but definately not comfortable at this point.   


So I tried my 600 and 70-200 2.8 on my 7D and in my opinion the lag time is about the same.   

Hey Mike,


       I repied several days ago....this is a REAL problem for shooters like me who have tons of experience in the field...

please have Canon address this...there is no work around for a the photographer....I just wasted 3200 dollars...could

have kept my main I have to shoot with my backup camera...another mk2...or make the painful leap to


Im glad you are all replying guys, as everyone has stated, this is a very big deal.