Hunting issues on my lens


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ombre

Senior Member
Sep 3, 2008
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#1
Hi guys,

Mainly I would like to know if anyone can tell me what my issue is known as and if anyone encountered it before... maybe can enlighten me on the cause too.

The lens is a Canon EF 24-85mm F3.5-4.5 USM. Recently, it has been on a hunting spree, even under bright sunlit conditions. While on other occasions, it seems fine. When I say 'hunting', it doesn't actually hunt the full cycle and not lock, rather, it hunts half cycles, and really rapidly. Looks like just "zooming" in and out.

It will go away after awhile and act like a normal lens, but once it misses focus again, it will start hunting and it hunts on every other object afterwards for awhile.


Just disclaimers:
1) I understand how normal focusing works and I did target high-contrast areas to test, I am certain its an error and not normal hunting.
2) My other lenses work fine, so I guess its not the body, body is a 20D by the way.
3) I have cleaned all electronic contacts, doesn't seem to be the problem.

I bought it 2nd hand from TCW, they told me they'd give me 3 months shop-warranty, when they say that, do they usually fix the lens on their own or send it to Canon?

Thanks in advance!
 

Jan 20, 2008
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#2
Just 1 point to take note,
What type of sensor you use for your testing ?

If you use a vertical af sensor to test on a vertical line,
then it may hunt cause it is not capable to lock onto target.
Same for horizontal sensor on horizontal line.

Does it happen on cross sensor ?
 

ombre

Senior Member
Sep 3, 2008
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#3
Yea I only used the center sensor so far, and I've been testing in real world conditions/objects.

Gonna send it down to TCW today, does anyone know how long they usually take for shop warranty?
 

Limsgp

New Member
Dec 16, 2005
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Singapore, Bedok
#4
Possible that there may be dust or dirt in the lens? (assuming no issue with other lens)

If the dust is of significant size and at some critical area inside or outside the lens.. it may affect the focusing? Did you try to use other focus points to test?
 

ombre

Senior Member
Sep 3, 2008
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#5
Sigh, sent it in to TCW for shop warranty repairs already, hope it turns out well. Even they couldn't really tell me whats wrong.
 

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