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11-01-2010, 02:18 PM   #1
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Focus problem on FA50mm

Hi,
Well I have just got my first dSLR, a K10d, and on it went my old lenses, a FA-50mm and a Sigma 28-200.
While playing with them, I noticed that the AF on the 28-200 is pretty fast and accurate, but I didn't get any AF on the FA-50mm - just a small movement, some noise and it freezes.

After a short check this is what I found out:
1 - Without changing any settings on the body, the 28-200 Autofocuses without a hitch, however there is a problem with FA-50mm. So I assume the problem is not related to body .

2 - On manual focus mode the FA-50mm does recognize when it is focused (I see the green hexagon lights up and a red square blinking). So the body focus recognition is okay.

3 - When I try to focus with FA-50mm there is a short noise, less than a second but the focus doesn't budge. It is the same behavior whether the lens is at infinity and I point it an object 1 meter away, or whether the lens is at 0.8 meter focus and I point it at the same object.

4 - I tried to clean contacts, using soft eraser, it didn't help. the Mechanics on the back seem fine (i.e. no damage visible).

5 - It seems to me that when I manual focus the FA-50mm the friction is much higher compared to the 28-200.

6 - the focus ring center-line on the FA-50 is not aligned with the lens center-line, i.e. The space between the focus ring and the ring below it is not-uniform, varying from 0.5mm to roughly 2mm.
see attached images.


So I think that the problem is the increased friction / misalignment, however my experience in dSLR is nil, and the last time i used my film SLR was something like 10 years ago...
So I would be glad to hear your ideas / thoughts - maybe it is a common problem with a simple solution... and whether I can fix it in home or do I need to get it to a service shop.

Thanks
Daniel

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11-01-2010, 03:22 PM   #2
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It sounds like this lens was clocked right there on the focus ring, resulting in internal damage. Might have to send it in if you want the AF to work.

Adam
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11-08-2010, 07:07 AM   #3
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Hi,
I have sent the lens to a service shop, they identified the problem with a malfunctioning (broken?) worm-gear of the auto-focus.
The fee they want for the fix is ~170USD, is it reasonable?

Thanks
11-08-2010, 07:20 AM   #4
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QuoteOriginally posted by koraldon Quote
Hi,
I have sent the lens to a service shop, they identified the problem with a malfunctioning (broken?) worm-gear of the auto-focus.
The fee they want for the fix is ~170USD, is it reasonable?

Thanks
Up to you. A used one here in good condition is about US$300.

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