Auto focus problem

rclarke80

rclarke80

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Rich
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Hi folks,

Has anyone any thoughts of what is wrong with my lens, it will autofocus but only if focus isn't far away. If it is it stops after focussing so much and then you need to press the focus button again until focus is achieved. Machine gunning the focus button is the best way to gain focus on a subject quickly but obviously that isn't ideal for some subjects. Manual focussing isn't an issue and the ring feels fine.

Thanks in advance,
Rich.
 
What camera and what lens?
 
Some lenses have a focus limiter switch on them, so it will not travel all the way from closest focussing distance to infinity, instead it will be limited in it's range.
When engaged, it will focus quicker, because it hasn't got so far to travel when focussing.
This is why we need to know which camera and lens, to work out if this is the case.
 
Oh, canon 1dmk3 & 4, canon 17-35 L f2.8 lens.

A limiter would seem to explain it if that is the case, as it will work eventually after a few presses.
 
I don't think that lens has a limiter, does it do it on both bodies?
 
My old 17-35 developed exactly the same symptoms that you''re describing. The focus motor drives the focusing group by friction (to allow FTM focusing) and the nylon friction piece had worn so that slippage occurred.

Bob
 
Yes both bodies. Will try the contacts but doesn't sound good hearing about your identical problem Bob.

Thanks for all your input though. I can live with it if repair is expensive though.
 
You can eliminate (or confirm) a contact problem by trying the DoF preview button....if this works when the focus doesn't then the communication and power contacts are fine.

Bob
 
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