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05-15-2014, 07:40 AM   #1
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New model sigma 18-250 lens not focussing correctly on k3

Hi all. A weird one here: the newest model sigma 18-250 lens we bought 18 months ago quit focussing correctly at focal lengths 24 and under. It do focuses about 50 feet closer than it should. It's fine at the longer focal lengths. The kicker: works fine on Karen's k5iis. I did put in the latest firmware recently to the K3, and every other lens works fine on the K3. I also cleaned all contacts. Any suggestions? I think it's gonna need a service trip to sigma.

05-15-2014, 06:18 PM   #2
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Original Poster
Obviously no one else ran into this.
05-16-2014, 08:02 AM   #3
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I had time to look further into the issue today, plus I was going to give sigma some test pics. I forgot that I had pulled all my B&W uv filters from my lenses, including this one. Well it changed the focus fine tune from plus 3 to minus 7. Now it works fine on the K3. Not sure why the 18-24mm focal length only was affected, but fortunately the minus 7 did not adversely affect the other focal lengths. Weird again the focus fine tune stayed the same(0) on the K5iis both before and after removing the filter. I think the K3 is really sensitive to any aberrations it has to focus through?? Anyhow, a few folks here have been saying for awhile that any filter can affect focus, and I used some of the best ones(mostly b&w, some hoya super hmc) and nearly all affected focus and corner resolution. I am a believer.


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