I have a new Canon 400 f5.6 lens that I use on a Canon 1D Mark IV & when I use it I find when I have it set to al-servo and focus on a subject and get a clear focus if I don't hold down the shutter button it drifts out of focus. Is is normal
Paul
Feb 09, 2013 at 07:40 AM
Lars Johnsson Offline • • • • • • • Upload & Sell: Off
I'm not sure that I understand your question? If you activate the AF with your shutter button, then you must press it if you like the focus to follow a subject. If you don't press any button on your camera and AF will not work
When the shutter button is fully released, the camera stops the AF function, and the lens AF group remains on the last focusing distance just before the camera terminated AF.
However, if you continue to observe your target in the VF after letting go off the shutter button, you might see defocus develop because either your target and/or you have moved.
That is the way it is supposed to work. If you see anything different, then your gear may be in need of service.
MS PHOTO wrote:
I have a new Canon 400 f5.6 lens that I use on a Canon 1D Mark IV & when I use it I find when I have it set to al-servo and focus on a subject and get a clear focus if I don't hold down the shutter button it drifts out of focus. Is is normal
Paul
Yes, because you are moving the lens slightly. Try the same thing using a tripod.
