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09-08-2008, 07:32 AM   #16
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QuoteOriginally posted by jacksonpritt Quote
Here's a sample from my lens...

Shot taken at 15mm 4.5, 1/90, steadied on a tripod, at ISO 800.

The corners are really, really blurry... is this normal at this focal length and aperture, or should I send this in to get looked at?

Flickr Photo Download: sigma_example
Mine does the same thing at 10mm. I don't think it's a problem, just a characteristic of the lens at that focal length. Your center subject is sharp.

09-08-2008, 10:18 AM   #17
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Well if the corners should be that blurry @ 10mm then I sent the lens for service for nothing Duh, the shopkeeper said the left side is too soft in my case so let's see what the service guys do with it. Maybe I get it back even more screwed then.
09-08-2008, 11:03 AM   #18
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QuoteOriginally posted by Maffer Quote
Well if the corners should be that blurry @ 10mm then I sent the lens for service for nothing Duh, the shopkeeper said the left side is too soft in my case so let's see what the service guys do with it. Maybe I get it back even more screwed then.
Post some pictures after you get it back. If it's not supposed to be like that, it would be good to know.
09-08-2008, 11:17 AM   #19
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Will do. Well here's the brickwall sample I took which the shopkeeper took a look at:
http://www.students.tut.fi/~koski7/pix/pentax/brickwall_f4.jpg

I would understand soft left and right side if they were equally soft but if you look at that shot you will notice that the left side has a motion blur kind of softness whereas right side is much more controlled and sharpish. If the left side of the picture has any kind of text it makes eyes hurt trying to read it while the same text on the right side is perfectly readable.

09-08-2008, 01:14 PM   #20
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How far were you away from the wall? And were you exactly perpendicular?
As folks have mentioned, UWA lenses have issues w/ curvature. If you were exactly perpendicular, then yes I'd agree it has a possible decentering defect...
Be sure to send images when you send the lens in. It helps them figure out what's going on (I think they use the EXIF info).
09-08-2008, 01:41 PM   #21
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I used leveling tool to get it as straight as possible. The shot is taken like 50cm from the wall as it was part of a chimney which ran thru the floors and was not wide enough to be captured fully any further back. And yes, I included test image links with the service report so they know what to look.
10-05-2008, 05:07 AM   #22
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Hmhmmh, so I finally got my Sigma back from the service. The funny part is that they did nothing to the lens but measured it with their devices. Result was that the lens is perfectly okay by all means. I discussed this pretty long on the phone with the service guy who insisted that the shopkeeper gave me false advice to send over the lens for service. Well apparently the service is correct about this one. 10mm end will be blurry on the left with this lens no matter what, unless you calibrate the lens with the body so that 10mm gives slightly better results. However this approach may screw up other focus lengths.

During the last 2 years this service department had replaced only two sigma 10-20mm lenses with really blurry left side. My lens was on the better side according to the measurements. So perhaps rating one sigma better than another copy when comparing 10mm edge resolution may just be placebo effect without very good measuring tools.

Well, gotta learn everything the hard way as beginner
05-09-2009, 03:49 PM   #23
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further question

QuoteOriginally posted by Maffer Quote
Hmhmmh, so I finally got my Sigma back from the service. The funny part is that they did nothing to the lens but measured it with their devices. Result was that the lens is perfectly okay by all means. I discussed this pretty long on the phone with the service guy who insisted that the shopkeeper gave me false advice to send over the lens for service. Well apparently the service is correct about this one. 10mm end will be blurry on the left with this lens no matter what, unless you calibrate the lens with the body so that 10mm gives slightly better results. However this approach may screw up other focus lengths.

During the last 2 years this service department had replaced only two sigma 10-20mm lenses with really blurry left side. My lens was on the better side according to the measurements. So perhaps rating one sigma better than another copy when comparing 10mm edge resolution may just be placebo effect without very good measuring tools.

Well, gotta learn everything the hard way as beginner
I have just gotten a new 10-20mm sigma (same as the one being discussed - the f4-5.6 style) and have the same left side issue. At 10-12mm, it improves by about f8-11, but the right side is really good at even f4. I never tested 16-20mm because for me that's emergency use only.

Questions:

1. Is the sigma explanation reasonable?
2. Is the lens in fact adjustable to correct, or "change", this characteristic? How?
3. If 1 and 2 are true, has anybody tried optimizing for 10-12mm?

I don't live where I can trivially exchange the lens until I find a good copy, so I'd rather get Sigma to deal with the one I have, if anything can be done for it.

Paul

06-24-2009, 09:11 PM   #24
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examples

I've added a couple of example pictures. I took these from the identical position, obviously moving the camera to where the subject was on the opposite side of the image for each picture (but maintaining the same camera-to-subject distance.) Focus was manual and not changed between the pictures. No post-processing except some color/curves adjustments and the cropping. These are jpeg crops from the original raw images from the K200. These were made at F4, 10mm. These are very representative of the other tests I've done.

It does seem like there is a common left-side image quality issue with these lenses. I'm still undecided as to whether to send the lens to Sigma for calibration, mainly because it seems like other people haven't had success with that.

I can't generate this kind of comparison on the K100. Maybe it just doesn't have the resolution. But I also can't generate the same results with other lenses on the K200, making me think the calibration problem probably isn't with the camera(?)

Paul
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06-25-2009, 07:52 AM   #25
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Hmm, ahh 'tis old issue. Well that's exactly what my copy does at F4 & 10mm but I stopped caring about it long time ago. I always use this lens at F8+ (usually F11-F16) which gives acceptable extreme borders. Back then I didn't know that UWA zoom lenses like this are gonna be somewhat soft at the extremes until you get something like nikon 14-24 for 2000$. I used my 18-55mm lens and was disapppointed because the extremes were more sharp than Sigma's extremes at 10mm.

The service guy explained that my copy was perfectly fine and tinkering with it could, in theory, make the left side a *bit* better but mess up the other focal lengths in some other way.

I would advice that you go take some photos for real with the lens at different focal lengths and smaller apertures (F8+). Take a whoooooole biiig bunch of photos and then go thru them in randomized order. When you happen to come by a photo shot @ 10mm and it really makes you puke without pixel peeping the left side @ 100% size, by all means send it for calibration.

Last edited by Maffer; 06-25-2009 at 07:57 AM.
06-25-2009, 09:17 AM   #26
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QuoteQuote:
Damn Britt: Another member Simonkit had two bad copies before he got a good one, I think someone else did as well. Those of us who have good copies love them.
Yes, my feelings exactly. My copy is awesome, with excellent quick focus. Even wide open the lens is surprisingly good. It would be hard to exaggerate the exceptional value of this fine lens.
06-25-2009, 12:08 PM   #27
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QuoteOriginally posted by Maffer Quote
Hmm, ahh 'tis old issue. Well that's exactly what my copy does at F4 & 10mm but I stopped caring about it long time ago. I always use this lens at F8+ (usually F11-F16) which gives acceptable extreme borders. Back then I didn't know that UWA zoom lenses like this are gonna be somewhat soft at the extremes until you get something like nikon 14-24 for 2000$. I used my 18-55mm lens and was disapppointed because the extremes were more sharp than Sigma's extremes at 10mm.

The service guy explained that my copy was perfectly fine and tinkering with it could, in theory, make the left side a *bit* better but mess up the other focal lengths in some other way.

I would advice that you go take some photos for real with the lens at different focal lengths and smaller apertures (F8+). Take a whoooooole biiig bunch of photos and then go thru them in randomized order. When you happen to come by a photo shot @ 10mm and it really makes you puke without pixel peeping the left side @ 100% size, by all means send it for calibration.
What I'm not understanding is why, if some lenses are indeed pretty good (or at least similar left-to-right), other lenses can't be adjusted to perform the same. I guess the problem is that I don't understand whether the "calibration" that can be done actually corrects something done wrong at the factory. If it does, it seems that any lens should be able to be made to perform as well as the design itself can perform. In other words, say you have two metal bars, one perfect and one bent to the left. If you bend the defective one to the right in a different location in the bar, you'll wind up with the front and back pointing in the proper direction, but it won't be strait, it'll just be bent twice. If that's the kind of calibration they're doing, then I can see where what you gain at one setting you'd lose at another. But it doesn't make sense to me that if all the elements are centered, the left-to-right performance shouldn't be identical, for better or worse, at every focal length setting.

Paul
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