problem with auto focus

[korys_ins]

I have been testing my 70-200 IS and sometime when Its on my 20D I

notice the auto focus is not working I have to detach and reattach

the lens is this common It only happened twice so far with this

lens , never had that problem using my other lens. Should I do

something about it or wait and see if it happened again I also

notice that auto focus does not work with setting AV/TV please

help.

[denisgermain]

it doesn't work at all

or you don't see the small red dot telling were the focus is? << if this the case you are most likely in AI Focus or AI servo mode...change it back to One Shot.... :)

[korys_ins]

yes I do not see the red dots or the exposure level indicator in the view finder at all

[korys_ins]

got it CF was on

[medina photography cherry]

This happens to me as well, Sometimes when I have the 70-200 2.8 (non is) I will push the button down half way to get focus and nothing. Sometimes I am to close to the subject and sometimes I accidently switch from 1-3metere to 3 to infintiy and being to close to the subject as well. Then there are other times where it just does not seem to work until I turn the AF from AF to manual back to AF. What is up with that anyway?

[dcheung]

I've experienced this one day with 135 F2 on a 20D and AI Servo mode. Later on I discovered i somehow accidentally selected all the focus points so it wasn't focusing to the plane i was pointing at. When this happens to you guys, double check you are using the focus point that you think you are using.