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09-04-2008, 12:07 PM   #1
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Blurry Sigma 10-20mm F4.0-5.6 EX DC?

Helloes fellow pentaxians! New to this forum and all that but got to start somewhere I guess. Too bad it's going to be a rough one for the first post. Not too long ago I decided to get Pentax K200D-kit to take some shots from my trekking adventures. The stuff worked great as should but I noticed most of my pics were taken with the wide end of the kit lense and while the quality was good enough for my humble requirements I decided I would like to go extra WIDE! Thus I ordered this Sigma 10-20mm F4.0-5.6 EX DC lens...

Now I received my copy only to note that it's one hell of blur machine compared to kit lense or any other working lense for that matter. I'm a bit lost here so if any experienced people could take a look at my test shots it would be greatly appreciated. It's brand new lense so better to send it back ASAP if need be.

Here are the sample photos (some are overexposed a bit but that's not the point). The blurrines (if I'm not paranoid here) appears on the left side of the photos. All pics taken with tripod and 2sec selftimer to prevent camera shake. No UV filter used (shop had ran out of suitable ones) so that might induce some haze perhaps. MASSIVE pics warning! Direct HQ JPEG conversions from PEF files at 10M resolution.

1. Close range shot of a magazine. Note the barcode on the right side of the image. It's easily readable. 10mm + F8
http://www.students.tut.fi/~koski7/pix/pentax/magazine1.jpg

2. Close range shot of the same magazine. Swapped so that the barcode now appears on the left side. Quite a bit blurred now. 10mm + F8
http://www.students.tut.fi/~koski7/pix/pentax/magazine2.jpg

3. Close range shot of some random religious newspaper trash. Note the blurry text on the left. Easily readable on the right. 10mm + F8
http://www.students.tut.fi/~koski7/pix/pentax/trash_f8.jpg

4. Close range shot of the same trash paper. Now with F22 instead of F8. Here the funny part, now the left side appears quite sharp but right side got a bit blurred instead...
http://www.students.tut.fi/~koski7/pix/pentax/trash_f22.jpg

***

A bit DoF testing with obvious blur on the left:

5. Street shot. 10mm, F8 and focus set at infinity. Infinity focus seems to lessen the blur on the left quite a BIT it seems:
http://www.students.tut.fi/~koski7/pix/pentax/road_dof_f8_10mm_infinity.jpg

6. Same street shot. 10mm, F8 and focus set at 1m on the scale. Note the sharp foreground, right side and center part (this seems to be sweet spot for hyperfocal focusing with these settings btw.) Left side if much more blurred than with infinity focusing:
http://www.students.tut.fi/~koski7/pix/pentax/road_dof_f8_10mm_1m.jpg

So, what would be your judgement for this particular copy of the lens? Am I just paranoid?

09-06-2008, 01:38 AM   #2
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Oh well, the shopkeeper agreeded that it should be recalibrated. Going to send it for service. Lucky that there is one in Finland.
09-06-2008, 07:33 AM   #3
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You might have a decentering defect (common flaw w/ Sigma lenses).
However, the Sigma 10-20 is definitely never sharp from edge to edge (unlike the Tokina 11-16). You have to set it to f/11-13 to get best performance (mine is sharpest in the center at f/8 but sharpness is more even on the edges at f/11)...
09-06-2008, 10:03 AM   #4
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Aye, you are right. With smaller apertures the problem gets carried away somewhat but still not 100%. I think that at least left and right sides should be equally soft - not like this one, left side blurring like hell compared to right side.

09-06-2008, 10:46 AM   #5
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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.
09-06-2008, 10:56 AM   #6
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Well I already like this lense be it blurry or not Too bad I cannot take it with me to the forest next week as it's going to the service.
09-06-2008, 11:46 AM   #7
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QuoteOriginally posted by Maffer Quote
Too bad I cannot take it with me to the forest next week as it's going to the service.
That sucks.
09-06-2008, 01:47 PM   #8
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QuoteOriginally posted by Damn Brit Quote
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.
I've been noticing that my 10-20 can be a bit fuzzy at the edges too...
Is there a specific test I should do to see if my lens is properly calibrated?

09-06-2008, 02:02 PM   #9
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Here's a sample from my lens...

Shot taken at 15mm ƒ4.5, 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

Last edited by jacksonpritt; 09-06-2008 at 02:56 PM.
09-06-2008, 02:16 PM   #10
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The Sigma 10-20 can certainly be a frustrating lens, at least the search to find a good one is. Luckily my 3rd copy is very good & I'm now delighted with it but it's essential if you buy a 10-20 that you check it out....

I think at 10mm any lens, at least in this price range, will suffer some distortion - the 10-20 gets pretty decent at F11 & at 12mm/F11 is very good.

Jacksonpritt....is that a genuine photo from your 10-20 or have you induced the blurs, if it's genuine that's a pretty awful copy you have !!

simon
09-06-2008, 02:54 PM   #11
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QuoteOriginally posted by simonkit Quote
The Sigma 10-20 can certainly be a frustrating lens, at least the search to find a good one is. Luckily my 3rd copy is very good & I'm now delighted with it but it's essential if you buy a 10-20 that you check it out....

I think at 10mm any lens, at least in this price range, will suffer some distortion - the 10-20 gets pretty decent at F11 & at 12mm/F11 is very good.

Jacksonpritt....is that a genuine photo from your 10-20 or have you induced the blurs, if it's genuine that's a pretty awful copy you have !!

simon


It's 100% genuine, and the only retouching I did was to edit the levels a little.

I've only had the lens for a couple months (bought it from Adorama through Amazon), so I guess it's time to contact Sigma's customer service... Anybody got any advice or information about their return process/policies?
09-06-2008, 02:57 PM   #12
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I think you need to get it to at least F8 otherwise the DOF is going to be too flat for shots like that. F4 could account for some of that blurring.
09-06-2008, 03:23 PM   #13
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Good point, Damn_Brit.
I'll try taking some test shots tomorrow and posting them here to see if the quality is similar to what other people get.
09-06-2008, 03:46 PM   #14
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QuoteOriginally posted by Damn Brit Quote
I think you need to get it to at least F8 otherwise the DOF is going to be too flat for shots like that. F4 could account for some of that blurring.
Missed that, didn't read the focal info

At F8 & definitely F11 "blurring" should be confined to the extreme corners
@ 10mm & even this should reduce noticeably at 12mm, probably still a little blur evident at 100% although mostly neglible in "real world" shots

simon
09-07-2008, 12:40 AM   #15
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QuoteOriginally posted by jacksonpritt Quote
Here's a sample from my lens...

Shot taken at 15mm ƒ4.5, 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
Righto, that is pretty similar with my case. Right side of the image looks better than the left and the left is blurry as hell @ 10mm. 12mm makes it a bit better but the left side blurring is still pretty noticeable. From 14mm onwards, when using smaller aperture like F/11+, the blurring has vanished almost completely.

Anyways, let's see what happens after the service.
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