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07-22-2009, 09:24 AM   #1
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Question for Sigma 10-20mm (old - 4-5.6) owners

In my ongoing pursuit of getting the entire frame in focus and at least moderately sharp... I'd appreciate if anyone with the lens would try letting it autofocus on whatever body you have, while aiming at a very distant (as near to infinity as possible) object, and let me know what the focus scale reports.

Also, if you can focus manually (I can't, really - maybe the pentaprism cameras would be better at this, or maybe a magnifier would help), what does the focus scale read when you manually focus on infinity?

Thanks

Paul

07-22-2009, 03:01 PM   #2
axl
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at 10mm it's easy:
f8 (f5.6 will do but 8 is sharper in corners), MF at 1m and happy shooting. With these settings everything from 0.5m to infinity shall be in focus and sharp (if not, check your ISO/shutter speed or you have faulty lens.)
I tend not tu use AF @ 10mm. Simply because the size of the cross type senzors and the massive FOV makes it nearly impossible for camera to know what your intended target is.
Magnifier helps (I'm using OME53) but not much, so raise your hopes too much.
AFing at 10mm my lens usualy stops between 1m and infinity, only on very specific ocasions it goes to infinity ( again remember that at 10mm even @f4 the DOF is so huge that most of the times you'll be fine).
As far as MFing goes scale on my lens seems to be accurate (here remeber that the distance on the scale reports distance between target and focusing plane! efectively sensor - not between the target and lens)
good luck, hope this helps

BR
Peter
07-22-2009, 05:35 PM   #3
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I just tried with mine. When using both AF and MF on very far objects, the focus scale is where the infinity mark is.
07-22-2009, 06:30 PM   #4
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I guess I forgot to provide my own information after asking for everybody else's. Like I said I really can't MF so that's a non-issue for me. AF is 1M/3ft at infinity.

The behavior I'm seeing (and described in previous posts) is that on 10mm and f4, with a distant subject and the marked 3ft AF focus, I've got a razor sharp (IMO) right side and fuzzy/smeared left side. But now I find that if I manually put the focus on the | mark for infinity (the lens focuses past that, but where the vertical part of the |- is), I get both left and right sides equally soft, but not glaringly fuzzy/smeared. Interestingly, stopping down to f9.5 or so helps the 3ft focus quite a bit (the left sides picks up, and the right side stays crisp), but there are much less impressive gains when stopping down with focus on infinity.

I honestly never thought about this before I got this lens because with my 17mm (full frame) lens I just cranked the focus to infinity (it didn't focus past the infinity mark), backed off a bit, and everything was sharp. I didn't even bother focusing except obviously for close subjects.

Overall results are probably better with just using the | mark than using AF / 3ft. focus, but still uninspiring.

Paul

07-22-2009, 07:13 PM   #5
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It sounds like your lens might be decentered. Take a picture of a brick wall or other flat surface. Make absolutely sure that you are pointing directly at the wall (perpendicular). Take a picture at F4 - you should see all four corners of the frame are equally in focus. If not, you should send your lens to Sigma for repair - the EX lenses have a 4 year warranty.
07-22-2009, 10:51 PM   #6
axl
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QuoteOriginally posted by tibbitts Quote
I guess I forgot to provide my own information after asking for everybody else's. Like I said I really can't MF so that's a non-issue for me. AF is 1M/3ft at infinity.

The behavior I'm seeing (and described in previous posts) is that on 10mm and f4, with a distant subject and the marked 3ft AF focus, I've got a razor sharp (IMO) right side and fuzzy/smeared left side. But now I find that if I manually put the focus on the | mark for infinity (the lens focuses past that, but where the vertical part of the |- is), I get both left and right sides equally soft, but not glaringly fuzzy/smeared. Interestingly, stopping down to f9.5 or so helps the 3ft focus quite a bit (the left sides picks up, and the right side stays crisp), but there are much less impressive gains when stopping down with focus on infinity.

I honestly never thought about this before I got this lens because with my 17mm (full frame) lens I just cranked the focus to infinity (it didn't focus past the infinity mark), backed off a bit, and everything was sharp. I didn't even bother focusing except obviously for close subjects.

Overall results are probably better with just using the | mark than using AF / 3ft. focus, but still uninspiring.

Paul
sorry to say so, but this sounds very much like a faulty lesn.
If it's new, return it, if it's within warranty, send it in...
BR
Peter
08-20-2009, 05:40 AM   #7
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update

I have sent my lens back to Sigma USA, and had it returned after about 2.5 weeks. The focus behavior is now slightly different, I think, but the overall results are the same. The focus is simply different on the left than on the right.

I'll contact Sigma again and report what happens next.

Paul
09-22-2009, 02:43 PM   #8
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update

I have heard back from Sigma. They have tested the lens and are sending the lens back for a second time, with no additional changes, along with their resolution test results. They cannot reproduce any difference in left-to-right resolution. My tests (which I sent them) on both my K100d and K200d show dramatic differences in focus from left to right. Sigma seems to be sincere in that they believe the lens is functioning properly, but I'm equally sincere in believing it doesn't. I have tested my other three lenses and cannot detect any focus difference from the left to right side of the frame.

So there is no happy ending to the story. I suppose I can try to buy another 10-20mm and test it (I have no other way to obtain a lens for testing), and if it works better on my camera, sell the original. Assuming the Sigma tests show what Sigma says they do, the lens must work well on whatever camera Sigma is testing them on (they are using, apparently, a Pentax camera for testing - I'll ask which model.)

Other than chalking this up to some compatibility issue with both my cameras(?), any other suggestions?

Paul

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