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6 Days Ago   #1
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Focusing problems with Sigma 17-50 on KP

Okay, I have something weird going on. I bought a (second-hand) Sigma 17-50 f/2.8 HSM OS and paired it with my KP. I already own 2 HSM Sigmas that I'm quite pleased with. The AF is nearly always fast and on target. However, as soon as I started playing with this lens, I noticed that it was hunting an awful lot and often refused to lock focus, unlike my other Sigmas. I cleaned the contacts - no difference. As I bought the lens in a camera shop, I have a 12-month guarantee, but before returning it, I want to make sure that I'm not doing something wrong.

Now the weird thing is: initially I'd turned the OS on the lens off and the in-camera SR on; that's when it didn't work. I then decided to do it the other way around: OS (lens) On - SR (camera) off. Lo and behold: it seems to work flawlessly: fast and accurate focusing; no hunting to speak of .

I've no idea what's going on. In an in-depth comparison test here on PF it says 'based on our testing we found no statistically significant difference between the in-lens and in-body stabilization systems.' As my experience seems to be different, could this vary from camera to camera?

If anybody has any ideas/suggestions, I'd love to hear them!

Thanks in advance!

Lidy

6 Days Ago - 1 Like   #2
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Sigma on Pentax are known to be a bit finicky... but it seems like you found a way to make the focus work every time - so why not stick with that?
I think only some very early copies of the Sigma 17-50 2.8 had in-lens OS, so you might be lucky to have it!
6 Days Ago - 1 Like   #3
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Sigma 17-50 was designed and produced way before KP was released. I would guess there's an incompatibility between the lens and the camera.
This lens doesn't support updating firmware, so no way of resolving the problem on your own.


At least it works in certain configuration (as you described)
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Mine did weird also. At first all was well but then AF accuracy started failing. Mine is without OS. Calibrated the lens a couple of times and it was all over the place. I sent mine to Sigma under warranty. Repair order said it was calibrated on a K3, vague enough. I've had it back 6 months now and it works. Whatever adjustment it was, Worked.

6 Days Ago - 1 Like   #5
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I had the lens without OS and used it mostly on a KP and on a K-50, it worked fine without any problems.
5 Days Ago - 1 Like   #6
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Original Poster
Thank you all for your comments!

I'm afraid I spoke too soon. Yesterday I gave the lens an outing and it was H-O-R-R-I-D! Spinning a lot, but hardly ever focusing, whatever setting I used. Sometimes it seemed to be worse on the wide end (17mm), and work on the tele end, but then it changed again. It drove me nuts.

I've decided to return it and ask for a refund. Somehow I think the problem may be related to both the lens and the body having a stabilisation system. Or maybe I just had a Monday morning copy. As I really like and want this lens though, I've ordered another one. This time one without OS, from a reputable UK seller whom I've bought from before: SRS Microsystems. I'll have a 30-day approval time + 1 year guarantee.

Hoping for the best - keep your fingers crossed please,
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