Critical focus: what the F
 

Hey gang. Haven't stopped by here in way too long!

Writing in since I am looking at some ~500 pics I did for a shoot and about half of them are out of focus. That's not good. I'm using a Canon 30D with a 28-135mm f3.5-5.6 lens I got years ago. The shoot was indoors, at night, ie "pitch black". There where some useless room lights and I always set up a model light so I could see to focus. The real light was from cold speedlights, PW triggered. Model and light position was mostly the same per pose (~50 shots or so) but I moved around with the camera a lot during a pose. Settings were manual for the lighting to work.

I always tried to focus on the face, manually, almost every shot. But I'm looking at them now and it seems the face would be out of focus, but the chest/arm/etc is consistently in focus. I might be committing a focus no-no by zooming in, focusing, zooming out. I've heard lots of yays and nays for that technique.

Looking at the metadata I could not isolate the out of focus shots to a certain stop, shutter speed or focal length. Here's the most likely problems I could come up with:

Lens problem
Focus error (I hope not)
Not allowing tolerance in DOF

I was wondering if anyone had anything I can try before I go nuts and build a 3-D focus test chart. The most damning thing is that I shot hundreds of pictures with the same lens a few months ago, total run and gun (autofocus, Program Auto, ETTL, flash on camera bracket) and that was some of my best stuff. I think my focus technique sucks (learned it from a pro) or I am in a lower stop then I can handle (but 3.5-5.6 isn't THAT low... is it?).

Thanks for any help and for reading all of that!

Additional:
I was messing with the shutter speed on some of the shots and it might have gotten as low as 1/125 in some of them. I know faster is better, but since nothing was really moving quickly in these shoots I thought I'd be safe. Could that be the problem? Thanks again.