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02-26-2014, 04:48 PM   #1
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Sigma 10-20

I have an opportunity to pick up this lens at a fair price locally and am wondering if I have any recourse if its a bad copy as well documented here on PF. The seller says he got it as a demo and doesn't shoot Pentax so is selling it along with k5 body.

So if I find a problem after purchase and the seller won't allow me to return, what will Sigma do for me?

02-26-2014, 04:58 PM   #2
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I am guessing they will ask you to pay for servicing if its required.
02-26-2014, 05:17 PM   #3
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QuoteOriginally posted by hobkyl Quote
So if I find a problem after purchase and the seller won't allow me to return, what will Sigma do for me?

This is a very good question...I'm currently trying to purchase a used 10-20mm and I fear that if I buy a bad copy and if I send it to sigma or anywhere else that I will end up paying more than what I paid just to get it fixed..
02-26-2014, 05:25 PM   #4
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i have the variable aperture version of the lens. back in the day when i was buying it i read a few reports on decentering problems. dont know how wide spread it is. the one i bought is perfect, sharp and wonderful lens. if it comes decentered, dont count on sigma fixing it for you. usually such adjustments are too expensive for out of warranty service. if the price is right, i would totally buy it.

02-26-2014, 05:46 PM   #5
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Don't even think about buying a 10-20mm (variable aperture, at least) except from a reputable vendor that allows you to return the item without restocking charges or fees (except maybe shipping.) The only thing worse would be buying a Pentax 55-300 without those assurances. You can't count on any manufacturer to help you with decentering, even if the lens is under warranty, unless it's a truly horrible case.

I did miss the part about it being a local sale on my first read. If you can test it thoroughly before purchase - like 50-100 images under varying conditions, and have time to examine the images carefully on a decent-sized screen - then that's different than buying on the 'net.

Last edited by tibbitts; 02-26-2014 at 06:23 PM.
02-26-2014, 06:48 PM   #6
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Shoot some brick walls and other fun stuff, take the images home, tell him you'll get back to him with the money if all checks out OK.
03-03-2014, 09:03 AM   #7
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what is the best way to know if the sigma 10-20 is decentered? what are the best ways to test out or what things to look for in this lens to really notice if you have a good copy or not when purchased new or used?
03-03-2014, 10:07 AM   #8
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QuoteOriginally posted by ILLmatic173 Quote
what is the best way to know if the sigma 10-20 is decentered? what are the best ways to test out or what things to look for in this lens to really notice if you have a good copy or not when purchased new or used?
There specific tests for decentering, and you'll find them if you search, but you don't necessarily need them. Just take pictures with detail across the frame and examine the results critically.

The brick wall thing doesn't always work the way you'd expect at very wide settings and wide open, because of a combination of focus field curvature and just the fact that the various parts of the wall will be at substantially different distances from the sensor. But what you're looking for is inconsistency across the frame. Just because the edges are a little blurry that doesn't mean the lens is bad, but if some edges or corners are blurrier than others, that's what you're looking for. What I've done with wide lenses has been to mount five 8.5x11 printed resolutions charts on a flat wall, one in the center and the others in the corners, and, even at f11, bad copies have been much blurrier in some corners or edges than others.

You do need to test at various focus distances and of course at different zoom settings, because many lenses will be off at some settings, but not others. So testing becomes a pretty extensive process.

03-03-2014, 10:30 AM   #9
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QuoteOriginally posted by tibbitts Quote
There specific tests for decentering, and you'll find them if you search, but you don't necessarily need them. Just take pictures with detail across the frame and examine the results critically.

The brick wall thing doesn't always work the way you'd expect at very wide settings and wide open, because of a combination of focus field curvature and just the fact that the various parts of the wall will be at substantially different distances from the sensor. But what you're looking for is inconsistency across the frame. Just because the edges are a little blurry that doesn't mean the lens is bad, but if some edges or corners are blurrier than others, that's what you're looking for. What I've done with wide lenses has been to mount five 8.5x11 printed resolutions charts on a flat wall, one in the center and the others in the corners, and, even at f11, bad copies have been much blurrier in some corners or edges than others.

You do need to test at various focus distances and of course at different zoom settings, because many lenses will be off at some settings, but not others. So testing becomes a pretty extensive process.
Thanks...I'm currently trying to buy a 10-20 f3.5..and might get one on eBay and I wanted to make sure so when I get it can check it out. I guess I still have to do some more extensive research on it before then..thanks again
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