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12-03-2012, 03:54 PM   #1
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Sigma 17-70 2.8-4 AF problem

I have a Sigma 17-70. It's my only non-pentax lens and it's acting strange IMO. Wondering if it's normal.

The AF is quite "jerky" and not as smooth as with pentax lenses, but the AF is still very sharp. The problem occurs on both a K5 and K20D

Camera is in AF.S

Here is a video


Last edited by absolut239; 12-19-2012 at 06:55 AM.
12-03-2012, 04:58 PM   #2
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Not normal. It should focus quickly and smoothly- I would return or exchange it ASAP.

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12-03-2012, 05:50 PM   #3
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My Sigma 17-70 does that, and a few others on youtube does the same (on Canon also). Dunno if the small sample are bad, but I couldn't find many other samples to compare with.


If you bump the volume up hugely you can hear it.
12-03-2012, 06:30 PM   #4
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How long have you been using it? Did it come from the factory like that? Did it ever become worse?

Thx for the answers

12-03-2012, 06:44 PM   #5
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About half a year now? It's the same as day 1. Mind you, it kinda sucks at AF on the long end (50-70mm), so I usually zoom to 50mm and focus, then zoom the rest of the way.

It can be slow in dim light. Pretty quick in bright light. Weird shuddering motion... but my Sigma 50 1.4 has a very light shuddering motion when doing minor corrections. On bigger motions, the Sigma 50 1.4 is completely smooth.

Hasn't failed me yet, but I don't know if it's normal. I posted a thread up once before and youtubed a few vids, and it looked like a few other people's had the same type of focusing and didn't complain. Way too late for me to return mine, so if I were you, I'd return and swap and see how a new copy is.
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