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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

yes thats true there are two distinct problems:


1.  utilization of the AF-assist beam.  to the extent that the real problem is AF low light performance then perhaps #2 below is also important in this context, but my point here is that this particular test condition is easy to reproduce with great consistency, and there appears to be a marked lack of performance utilzing specific flash models, i.e 600 ex rt and 580 ex ii. 


2.  re:  FM forums and actual low light AF performance.  Yes, there is more variation here (RustyTheGeek returned his first 5D3 and the replacement worked better), and the tests exposed to date are all over the map without specifying the EV level, for example.  But yes, anectotally we have evidence (emperical at least) that the 5D3 accuracy comes at a penalty in terms of AF lock time in "low light" whatever that means to the user conducting the test.  Beyond the emperical and anectotal I have not seen a test constructed with repeatable consistency that shows "lesser" cameras performing better, i.e. under certain EV conditions within the specifications of both cameras, for example.



echelonphoto. I also did this with a link to Canon Rumours about the subject. Here is the FM one.



Thank you for this,


I for now am thinking that you might well be one of these 'canon registered users'....


so thanks for the update Mike, at least we know that you are still with us 🙂

to be honest I have been thinking of purchasing a MKIII, coming from an old 350D....and reading issues like this and the 'light leakage' makes me worried and will be holding off until further news..
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

Most people would never notice the light leakage But.. avoid 1 or 2 in the 6th digit of the serial number.

Cheers for that but it would quite difficult to do qhen ordering via online..


This is where we in the UK & Europe can get our savings as we feel the pricing by Canon  is 'ripping' us off and subsidising other markets.

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

New post on AF on the canon rumor forum.


Canon is listening, and we appreciate your comments.

We are still investigating and any updates will be shared as information becomes available.

Thanks for your feedback and participation in our forum.

Fantastic!  Thanks for letting us know.  (I'm happy to send in my gear if you need to evaluate it and confirm noted behavior.)

outstanding,  Naomi; this is awesome.  you just calmed a great many folks.  thank-you!  just to know that Canon is listening is great encouragment I cannot tell you how much that is appreciated