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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

There are two issues of interest, at least to me 🙂 .  the issue addressed specifically by this thread is the use of the AF assist beam from a speedlite.  my testing shows, on my own 5D3, that this works very well.  at essentially "pitch black" conditions, my 5D3 works beautifully with AF assist, where the 580EX ii paints a nice pattern of light on the subject,enabling the camera to lock focus instantly.  within reasonable distances of course; 



the other issue at work is the AF performance itself in low light, without AF assist from a speedlite.  Canon specifies that the AF system is sensitive to EV -2, using the center AF point, f/2.8 and I assume a high contrast subject. 


 I performed an approximate test of this as well, by creating a lighting condition requring .5sec  at f/2.8 and iso 6400 to obtain a good exposure (thats EV -2 if my calculations are correct.), and my 5D3 captured focus just fine (I even acheived focus at  EV -3 but it wasn't dependable).  it takes a while (sometimes a few seconds) but this is, in my opinion, reflective of the accuracy and retry-credence algorithms present in the camera.  I have no problem taking that long to focus in that level of light because I'm usually not in a cave :-).  At that level of light, you can hardly see the subject anyway, much less a moving one :-).  keep in mind that the EV -2 sensitivity requires the center point.


in some ways, my tests were crude, i.e. I depended on the cameras own meter to roughly approximate EV -2.  In other ways, my tests were severe, in that I was using a 100mm macro f/2.8 handheld. I thought it was impressive to see the AF system lock onto what it surely sees as a moving target with very little light.  FYI I was using the default as-shipped focus mode. 


I repeated the above tests with my 70-200 f/2.8 IS II, obtaining similar results.  At approximately 15 feet subject distance and approximately EV +3, the AF assist even enabled focus on a very low contrast, dark subject (a treadmill belt, lol).


I can absolutely confirm a vast improvement in AF lock after the firmware upgrade, but it's specifically when using the IR assist. 


I've never had any issues with my 5D3 and 70-200 combo with either the old or new version of that lens and I shoot lots of low-light events including weddings.  In very low light the center point is sometimes the only one that will lock, though.  It's not going to lock in near darkness, but I don't have any complaints at all with that combo and I use it a lot.


If you're getting performance as bad as you say in a reasonably low light, you probably have another problem.



i can assure you that i dont have another problem... when i have two seperate 5D3 and 2 580EX II ... with two different lens.. on it... a 24-70 and a 70-200mm ..and they are both patched to the latest firmware and all using centre point focus.. and im still getting that issue ?????

highly unlikely

As an observer of the different experiences here I can assure you studiorl, that something about your two cameras is different. At least, something is different about the way you describe your two cameras, compared to the way I and otheres are describing theirs.    it is not unlikely at all for two cameras to have the same mfg defect, esp. if they are early in the product life cycle and come from the same production run. 


It would be fascinating to compare performance using the EV standard that I refered to.  I'm happy to re-construct my tests as well to compare notes.  It should not be too difficult to create similar "enough" scenarios and compare results!


Please add my concern.  I have a new 600EX and a 5D3 and the performance in low light is terrible with a 24-105 F4.  I got much better performance from a flash with my first rebel many years ago.


On my older Canon flashes, you could see a pattern projected on the target when the flash fired its focus assist.  Now you don't.

Actually...its not the fine on the 5d can clearly see the beam.

sold my 5d mark 3 the interim...I got a 1ds better with the beam...but still not as good as my 5d mark2...also

the write time to review on the 1ds is deplorably slow, but i love the viewfinder! Why couldn't they put this viewfinder on the

5d series? Well I guess Canon wants you to buy lots of bodies...because not one of them has everything you want.


Looking back at my brief 4 months with the 5d mark does have a lot going for it....more accurate AF in general...shooting at ridiculously hi iso with no noise...great processor...the only thing wrong was that stupid

problem with shooting in low light with the flash beam. If they fix this problem...I will be buying another one.

I tried it on a close up, and you see the pattern. Unless my memory is poor, I remember seeing the pattern on regular distance objects. With the 600, it is not visible at normal picture taking distances. I remember being able to shoot in total darkness at night with my EOS 3 and, I think, the 480 flash, and getting instant focus and perfect pictures. Given what I saw shooting a party with the new rig, that would be impossible. My focus speed with a D5Mk3, a 24-105 F4, and the 600 was slower than a point and shoot. It was the first time I used the flash, and was greatly surprised by having to wait for seconds for focus lock with a flash and AF assist. My focus with assist turned off was much faster.


okay for us Brits:



Have still to test out the update but all went easy yesterday

EOS 5D MKIII + EF 24-105mm f/4L IS USM, Sigma DG 150-500 5-6.3 APO HSM, , EF 55-200mm 4.5-5.6 USM, Speedlite 430EXII

EOS 350D, EFS 18-55mm


I actually sold my original mark 3 because of the AF problem...just got another one and uploaded the firmware...what a difference! I think the camera is just about perfect now. The next crusade issue.....the 630 RT's....a great advance and design for profession flash.....but the recycling has let me down....I will be starting a new thread on this today.

click here to view the press release