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11-24-2009, 06:37 PM   #1
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Auto-focus doesn't auto anymore

I have a Sigma 1:4-5.6, 70-210mm, UC-II zoom lens that the auto-focus doesn't work on.
I'm pretty sure it's not the camera as my other zooms auto-focus perfectly.

In "auto" on my zx-50, although there is no auto-focus, it works fine. The camera reads the settings and adjusts the f-stop fine.

Has anybody had any experience with this or a similar situation?

11-24-2009, 07:10 PM   #2
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I don't have any experience with failed screwdrive AF lenses, but is the focus ring moving freely?
Did the lens take any knocks or falls recently?
Is the lens fitting properly onto the camera mount?
11-26-2009, 05:52 AM   #3
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Yes, Not sure, Yes...

Thank you for replying, Ash.
The focus ring moves like silk and retains focus through-out the entire zoom range.
I'm not sure if it has ever been dropped or such. I bought it on e-bay for $15.50.
It does "click" in when it is put on the camera.
11-26-2009, 09:49 AM   #4

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I bought it on e-bay for $15.50
For $15.50 your lucky it worked at all.

11-26-2009, 11:28 AM   #5
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You might try cleaning the contacts with some rough paper or cloth. I was told that doing so sometimes helps. I have a Pentax-F 28mm that wouldn't autofocus, even though everything else was OK. The cleaning approach unfortunately didn't work for me and I had to have the circuitry repaired. But everything now works fine and I have a favorite lens that I initially bought very inexpensively. (With the repair it is now only a good price, but that is what sometimes happens when you buy used. It came from a thrift store as a package deal that I couldn't inspect.)

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