Ring USM Full-Time Manual Question

[drisley]

I have an 85F1.8 USM lens, and I had a 70-200F4 USM lens, both have full-time ring USM designs.
My question is, what is the proper procedure to use the full-time manual?
I always thought you would half press the shutter until the lens focuses, then while continuing to half press, you make adjustments with the focus ring.
However, when I do this, the lens keeps "shooting" back to the original focus point, and I end up "wrestling" with the lens to get the focus to where I want. It seems very hard to make minor adjustments in this manner.
Any tips?

[timmyquest]

You need to put your camera in "One Shot" AF mode. This will allow the lens/camera to do what you want it to.

http://www.photography-on-the.net/forum/showthread.php?t=38742

[samdring]

Just checked one of mine cos you had me wondering - keep half depressed and no hunt

[dtrayers]

Moving the focus ring while focus is locked is one way of forcing the 300D into AF-Servo mode.

Could it be that when you 'tweak' the focus that the camera is going into Servo mode?

[drisley]

Yup, thanks, you were right.
I switched to One Shot AF and everything is fine.
ANOTHER reason to use the Rebel hack! 8)