[ozlizard]

I am sure this topic has been covered before, did a search and couldn't find anything, so if anyone is aware of a previous thread on this subject please redirect me.
Apparently this is a common problem with this lens ie focus issues or blurring especially on the LH side. My lens is definatley showing signs of this problem. Have called the store where I purchsed the lens but as it is out of it's 12 month warranty they can't do anything. I beleive a few people have had their lens exchanged (by Sigma?) but I am assuming that this was done under warranty. Just wondering if anyone else has had this problem and how it was resolved, any cost involved etc.

[kenyee]

blurring especially on the LH side.

Yes, this is called "decentering". I had this w/ my Sigma 17-70 and needed to send it to Sigma twice (third copy seems ok so far).
You can't really fix it yourself...they have to replace lens elements, etc.

[tibbitts]

I am sure this topic has been covered before, did a search and couldn't find anything, so if anyone is aware of a previous thread on this subject please redirect me.
Apparently this is a common problem with this lens ie focus issues or blurring especially on the LH side. My lens is definatley showing signs of this problem. Have called the store where I purchsed the lens but as it is out of it's 12 month warranty they can't do anything. I beleive a few people have had their lens exchanged (by Sigma?) but I am assuming that this was done under warranty. Just wondering if anyone else has had this problem and how it was resolved, any cost involved etc.

There has been discussion, but it's not always easy to find.

I have not yet returned my lens to Sigma as I'm still experimenting after 3 months. However, if it was a USA lens bought from an authorized store, it would have a multi-year warranty. If you bought it with a credit card, that also might extend any warranty by 1 year. So there may be no rush. Just don't lose the receipt. I don't know but maybe Sigma does the same in your country. It is an EX lens, which has a longer warranty than a regular Sigma.

Meanwhile, I have found on the my K100 and K200 I get different results.

The K100 seems to autofocus the lens to about the expect scale locations. The K200 doesn't. When I let it autofocus, the scale lands at 3ft for infinity subjects. Set there, I get a super-sharp right side and fuzzy left side. If I manually focus using the scale (I can't see well enough to focus by sight), both sides and the middle are equally "fair." Even the center improves by f8, and the edges do, pretty similar to my 16-45 Pentax. The Pentax is equally horrible (but symmetrical) in different ways at f4, so that's why I haven't sent mine in. I think there's something wrong with the focus going out in different parts of the frame, but I'm also not sure that service will improve the net result. It's pretty easy to scale focus it with most of my uses for it. But I still might send it in, I'm just not sure.

The K100 and K200 are much, much closer on focus with other lenses, although not 100% identical. The scale barely moves when I move another lens between the cameras and aim it at the same subject, using autofocus. So that's kind of strange.

You might experiment with different focus settings and see what happens.

I have had very little success communicating with Sigma USA. I have left email and voice mail that has gone unreturned.

However the authorized service facilities are very responsive, although none admit to this being a problem with the 10-20. Basically they just want you to send it in and they'll look at it. Beware, typical claimed turn-around time between the different companies varies from days to months, so call ahead and ask if that matters to you (and it probably does.) Whether Sigma itself (vs. authorized service) would be more likely to exchange your lens I don't know (nor do I know if that would necessarily be a better resolution, given what seem to be very low odds of getting a "good" copy.)

Paul

[ozlizard]

Thanks very much Paul, I havn't tried to experiment yet, this problem wasn't that apparent with my K100 (although I am sure it was there..will go and check some older images), but seems to be more apparent on the K20, may be something to do with higher resolution. I started to look abit more closely after reading the reviews of this lens on this forum and reading the comments about how sharp this lens was. And I must admit that with the K20 when it is sharp it is very sharp...just find the softness on the LH side annoying.
I was told by the store where I purchased the lens that there was only a 12 month warranty but will call the suppler tommorow and see what (if anything!) can be done. Cheers.

[tibbitts]

Thanks very much Paul, I havn't tried to experiment yet, this problem wasn't that apparent with my K100 (although I am sure it was there..will go and check some older images), but seems to be more apparent on the K20, may be something to do with higher resolution. I started to look abit more closely after reading the reviews of this lens on this forum and reading the comments about how sharp this lens was. And I must admit that with the K20 when it is sharp it is very sharp...just find the softness on the LH side annoying.
I was told by the store where I purchased the lens that there was only a 12 month warranty but will call the suppler tommorow and see what (if anything!) can be done. Cheers.

I honestly did not notice this issue on the K100, but it's glaring on the K200. I suspect there are two reasons. The higher res is one; there is just more magnification at 100%. The other is the autofocus issue. The K100 focuses the lens to a place that renders both sides about equal. But with the extra resolution of the K200, you can see that you lose a little sharpness everywhere when you manually focus (using the scale) to where the left and right are equally sharp. That's hard to see with the K100. On the K200, when I get the image about equal side to side, it's just a little off everywhere, even in the center, vs. the right side and center when set on autofocus. Probably it'd even more obvious with the K20.

If I had only the K100, I wouldn't consider the lens defective, it's that much "better" (but probably not really) than the K200.

Incidentally, I have tried other lenses (kit lens, version 1, plus 16-45mm) on the K200 to make sure the same issue doesn't appear. I can't detect any side-to-side variation with those lenses on the K200.

Paul