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Tip for speeding up 5D focus

Ben Rubinstein

pro member
I've always found the 5D's focus in low light to be sluggish. It was one of the main reasons I went back to the 24-70L over the slower 24-105L, I needed all the speed I can get. I'm a wedding photographer and for the dances and those split second candid moments I need every millisecond I can lay my hands on. Unfortunatly I never noticed that my 1Ds which I used prior to the 5D was particularly faster, not in comparison to the lightening fast D2X for example.

I've known for a while that it was the AF assist that was slowing the focus down. I shoot with a flash constantly on camera, for main light or more often for fill. I've toyed with the idea of disabling the AF assist with its horribly slow (or so it seems when shooting action!) - activate/start focus/achieve focus/activate to check focus/allow shutter to release - workflow. For the off center points you can just forget it!

However I've been wary to switch it off 'in the field' being worried about what it would do to my focus in the real world, testing is fine but you cannot afford to test mid dance at a wedding!

Then I went to a wedding as a guest not as a shooter, first time in 3 years! The photographer there was shooting a 5D with a Metz hammerhead and was achieving focus without any difficulty. So last night at a wedding I switched off the assist and went for it. WOW, significant increase in speed and subsequent far more accurate focus with moving subjects as well as not losing shots as the camera goes through the whole routine of AF assist.

So from now on the assist is off unless in very low light, EV 5 or less, in a regular wedding hall with the lights on (admittedly a rare occurence these days!) or even in your own living room, you might find that the 5D is faster than you gave it credit for!
 

Alan T. Price

New member
Thanks for that info Ben. I had just replied to your related post in the 1D forum and I had suggested there was a deliberate AF slow-down when AF assist was on, similar to the slow-down you get when a teleconverter is attached to a lens. More of a just-in-case issue than a real issue, but one we're stuck with.

You might consider adding a post to that other thread too.

cheers
 
Do you think this is the case for the ST-E2 too? I mean do you think that 5D+ST-E2 will AF slower (than just 5D) in low light?

I'm asking because I'm seriously considering purchasing the ST-E2 to help my 50/1.4 AF quicker and more precise in low light. But following the logic you describe in your post it would mean the ST-E2 will actually slow the AF a bit.

Thanks,

Alex
 

Alan T. Price

New member
I have no way of knowing for sure, but it seems that it is caused by activating the AF Assist light, so I expect it would happen with any light source just so long as the camera thinks there is an AF Assist light.
 

Ben Rubinstein

pro member
Alex, it all depends on the amount of light, I'm shooting in pretty well lit halls where the assist is slowing it down, in a darker enviroment it may be the choice between innaccuracy and hunting versus speed and in very low light the assist will be faster.

What I'm saying is that once the assist is used the focus speed remains the same whether or not the light is at EV9 or EV4 (ish), i.e. the camera can do better than the assist speed workflow. Speed of lens still makes a noticeable difference as the camera can register the assist light reflected on the subject faster with a faster lens. This is from experience.

In short, my 24-70L will more or less focus at the same speed when using assist be it bright or dark. However your 50 1.4 will still focus faster even with assist enabled. You have to work out at what point the trade off is. I've only done this on one job and you need real world experience to judge, I'm shooting a bar mitzva tonight and two weddings later in the week that I intend to keep the assist OFF for, I'll report back my findings.
 
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