Original question on Autofocus.

AnimalRights

When I shoot gigs in this certain pub which has basically no lights I am fine for the 1st half or more of the gig, near the end it is almost impossible to focus and I have to guess, the lighting conditions do never change during the whole gig.
Now this sounds totally stupid but does the moisture from we say the crowd who obviously get bigger/drunker/dance more and create more sweat cause the air to effect the auto focus on the camera?
I know its may seem a crazy suggestion but I don't know how else to explain why the Camera suffers near the end of a gig!

Borderfox

Maybe it might be you absorbing the moisture mixed with apple juice?

Ballyman

Borderfox wrote: »

Maybe it might be you absorbing the moisture mixed with apple juice?

This would have been my guess too!!

AnimalRights

I left out that I use flash and drink is not the issue.

Calina

Hmm.

Although I doubt this would be an issue for you, I know from past experience that difficulties in autofocussing with my heavier zoom lenses are an indication that my battery is starting to deteriorate long before the battery indicator drops down to 1/3. Used to be a big issue on the smaller camera (with the less powerful batter).

I assume you're not using a battery intensive lens on this, are you? I'd assume that there's fairly decent battery life on the 5D which I seem to remember is what you're using camera wise.

AnimalRights

Battery on the 5D II as you correctly assumed is fantastic.

democrates

I've noticed this too after a few hours, even in fine conditions. It happened with this same 580EXii on the 450D too so the flash is my prime suspect. Maybe the af-assist beam isn't powerful enough when the batteries start to decline. I've been using energizer ultimates but the spend is mounting, must check out the sony 2700mAh NiMH rechargeables some have raved about, though at 1.2v x4 instead of 1.5v x4 I'm dubious.

What flash and batteries are you using AR?

AnimalRights

430EX II and I change the batteries b4 each gig so I don't think that is the issue for me.
I use duracell or the top of the range energiser.

DotOrg

if the venue is really hot the front of the lens can fog up slightly which will affect the cameras focusing ability. this is something i've experienced at really hot gigs but i just switch to manual focus

uprising

AnimalRights I think the heat/sweat/moisture may play a part in your auto focus problem, this is the chief suspect here as you said it's mainly a problem towards the end, as said earlier moisture on your lens will cause problems, I assume your fully aware of this and check it regularly.
Another thing that may affect your focus is the autofocus assist beam on your flash meeting tiny particles of steam/sweat/water that are in the enviroment and reflecting the beam back at the camera and confusing the autofocus system.
Why not try manual focus, and even full manual on your camera and wait for your subject to come to you and time it right, I know this may be hard with the subjects and the sporadic movement involved.
When the autofocus starts playing up, try a few pics on manual focus, give yourself as much depth of field as possible, and shoot in bursts of 3.
I sometimes add an extra 2 batteries externally with thin wire and insulation tape on my 550ex, it recharges the flash much quicker but can be a pain, and I'm not encouraging this in case it messes up your flash, but I've done it a few times without any problems. Also always use energiser litium batteries.
But I'd suspect its your autofocus assist beam causing your troubles.