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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

Hi Mike- 


I can confirm there is something strange going on with the 5Diii in low light.


I posted 2 targets, Target 1 at 20 feet (evenly exposed at 1.60, f2.8 ISO 400- I believe close to EV7), Target 2 at 4 feet underexposed 7 Stops on the same settings, and then focused back and forth 30 times with 3 different Canon bodies using a Canon 600 Ex Speedlite AF for focus assist.


Camera/Total Time through 30 focus locks (Target 1 is always faster BTW)


Canon 5Dii - 45 seconds

Canon 6D - 52 seconds

Canon 5Diii - 70 seconds


1. Im using a 24-70 2.8 L II lens, all shots were taken at 70mm

2. The underexposed Target 2 was 4 feet away, this is where it struggles.

3. Center Focus square





I should probably add a note about why I am going back and forth between the 2 differnent targets at different distances; Target 1 serves mainly to defocus. If im just aiming at target 2 and focusing over and over, its not a good measurement of the cameras ability to get that initial focus. 


Another point is that the average focus times for each shot work out to:


5Dii - 1.5s

6D - 1.7s

5Diii- 2.33s


But this is not what is happening. The focus lock on Target 1 (in good light) is always very quick, almost instantaneous. 


Focusing on Target 2 is taking longer than these average times. In fact, most of the time is spent on Target 2. 


Unless I had someone watching me with a stop watch it would be hard to know exactly (maybe we have to just video tape this whole event).


But I would say the times are closer to:


5Dii - 2.2s

6D- 2.5s

5Diii - 3.5s


I was planning on doing some more tests this weekend. If you guys want me to try something specific let me know. Ive gotten some good recommendations.



PS- If it makes anyone feel better, the Nikon D600 cannot focus at all on target 2 without it's focus light on. 😉

The use of 2 targets to "de-focus" or "refocus" or whatever is smart.  Perhaps you should test it using 2 targets that are both in dim light, rather than one in dim & one in bright?  I'd hate to let Canon off too easy by making the test too easy.


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"?

Mike?  Where did you go?  Anyone else from Canon out there?  Anyone at all?




Can anyone at Canon give us any information at all on whether this is being looked at?  Or what is the nature of the problem?  Will it be addressed in the firmware update?  Even if the information is that you still don't know anything, but that you are listening?


Any Canon person?




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"?


Im having the same problems. But i dont think its just an AF beam issue, my 5d3 is slow to focus in any low light situation.


As a festival/nightclub photographer, i bought the 5d3 to take advantage of the high iso along with the new af system. The 5d3 failed me. Im having to go back to the 5d2 which is amazing at focusing with low light and also using the af assist beams (ste2 transmitter and 580ii).


Im using it with these lenses


14mm 2.8L

15mm fisheye 2.8

35mm 1.4L

50mm 1.2L

85mm 1.2L


Ive experimented with the af settings in the menu and also with different focus points but still no joy.



This is extremely frustrating and totally unacceptable. How can Canon get something this important so wrong?








Canon 1DX have same problam

slower focus in dark with 600EX-RT

35MM F1.4

50MM F1.2

85MM F1.8

all my lens are same problem

i think its new focus system bugs

compare with my 1D mark IV

it's very slower on focus

please fix the problam quickly ^^



I would like to add my 2 cents also. I have shot for 6 years with the Canon full frame bodies...first the orig. 5d, then two of

the Mark2's....just got a mark3 and I noticed right away at a I was doing group photos using the center focus

spot in one shot mode....there was a distinct delay that is definitely not there in mk2....this is with the AF assist in indoor

lighting that is not even that dark. Never had a problem with the Mk2 and center spot with a flash is instant and I

can even follow action in a fairly dim room with it. The mark 3 is def better in AI servo mode, which is great...but I need that

one shot ability for portrait and reception shooting. I am using the 600 rt flashes with my cameras.


The one thing I can say is when the mk3 does focus always nails it accurately which is something the mk2 sometimes slipped up on.

This is info for Mike....I was using mainly the 24-105 lens...tried fine spot focus, regular spot focus and center group focus...

all in one shot mode. Most distances are about 8-12 feet and lens maybe zoom between 24-40mm.

I have that issue with the 600 ex rt i rented. slight lag from the auto focus lock to the shutter release. but i havent had major issues with af while using a custom bracket. sometimes the flash and the camera arent aligned properly with eachother so i slightly shift the camera to align it with the af beam. i really wish canon would update their oc3 cord with a built in af beam like the nikons do. nikons imo have always outperformed canon in lowlight. 

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