Does bigger aperature help autofocus?

[Bill_Jurasz]

A larger aperture will help autofocus because the lens, quite simply, is letting in more light. The problem with dim light AF is quite simply a lack of light. Let in more light and AF becomes easier for the camera to perform.

Note MF becomes easier as well. Much easier to manually focus in a bright viewfinder than a dim one.

[larry_angier]

Same problem, but I turn off the auto focus. I used to do this with a Hasselblad and got great results...

Zone focus your lens to about 6 feet and tape it in place. Shooting wide in a dark room with flash you should ace almost every dance photo at 5.6, more or less.

Sort-of like the Weegee approach during the black-outs of WWII when he shot using his built-in "radar" with his speed graphic.

[NillToulme]

Turning on a focus assist light can actually slow down the AF on the Mark II cameras (and from what I've read recently, the 5D as well). See this thread and this thread.

Nill

[Oleg_Shpak]

Originally Posted by Ron_Donson

Canon flash units and the ST-E2 provide an infrared focus assist light. It does improve the Canon DSLRs ability to focus in low light situations.

For whatever reason Nikon DSLRs seem to be much better at focusing in low light.

I tested 10D against D100 both with 50/1.4 a couple year ago. Nikon lost it is ability to autofocus later than Canon by 0.5-1 stop. And it was dark enough. I did not see any details on what I am focusing at.

[Oleg_Shpak]

Originally Posted by NillToulme

Turning on a focus assist light can actually slow down the AF on the Mark II cameras (and from what I've read recently, the 5D as well). See this thread and this thread.

Nill

Don't see why it should happen.
Anyway focus assist really help when autofocus lose its ability to focus completely or become random in low light.
To be honest I do not shoot anything in such conditions.

[Ross Throndson]

Originally Posted by chrisgiles

I've been using a 17-35 2.8 with my 1Dsmk2. If I'm shooting a wedding and it is time for dancing shots or anything inside dark rooms, my autofocus is worthless. Would a 35/1.4 increase the performance of the autofocus?
I'm very interested in investing in the 35/1.4 for multiple reasons, but curious if it will help the autofocusing in the dark conditions as well.

Chris

The f/1.4 would help alot with Autofocus....it's letting in so much more light than f/2.8... Plus you'll be able to see better!

[Alan_Ackoff]

Chris,

I was having focus problems in low light with my 5D and my Canon dealer suggested setting Custom Function 4-1 which gives you a focus button (the asterisk button) and leaves the camera in manual focus otherwise.

This gives you both manual and autofocus available all the time. It's eliminated 90 percent of my autofocus problems. Give it a try and see what you think.

Alan

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