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-   -   Testing the Sigma 17-70 (https://forums.steves-digicams.com/pentax-lenses-87/testing-sigma-17-70-a-131139/)

bahadir Oct 23, 2007 7:14 AM

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This is a casual shot I shot in raw and then converted into Jpeg with the Pentax Photo Laboratoryat default settings with no pp.

Guess the image does justice to the afternoon light : ) Still, I would like to hear your comments about the IQ since I considered returning the lenswhen I noticed the uneven results menifesting itself especially on the right 1/3 portion of the images!

I may send heavier crops if you think it is not possible to give a verdict at this scale.

Thanks in advance!

Focal length: 17mm; Aperture: f/8; Exposure t:1/125: Iso:100

#1) the whole picture

bahadir Oct 23, 2007 7:15 AM

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#2) Center

bahadir Oct 23, 2007 7:17 AM

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#3) Right

bahadir Oct 23, 2007 7:19 AM

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#4) Left

snostorm Oct 23, 2007 6:37 PM

Hi bahadir,

I can easily see the softness on the right in the full shot, but there are too many variables here to make a judgement from this one shot, IMO. Granted, a 17mm lens at f8 should give sufficient DOF to have just about everything in focus, but some other anomalous factor might be involved. I've seen too many shots that I've taken where something went wrong, but I couldn't reproduce the defect, and still can't explain most.

Now that you've seen a potential problem, my advice would be to take some more controlled shots, from a tripod of a subject where there are no distance variables (the "traditional" brick wall shot comes to mind) and look for the same softness to the right side.If, after that, you still see a significant difference from left to right, then I'd say that a return of the lens is justified, and you can accompany it with documented proof.

Scott

danielchtong Oct 23, 2007 10:05 PM

snostorm wrote:
Quote:

Hi bahadir,

I can easily see the softness on the right in the full shot, but there are too many variables here to make a judgement from this one shot, IMO. Granted, a 17mm lens at f8 should give sufficient DOF to have just about everything in focus, but some other anomalous factor might be involved. I've seen too many shots that I've taken where something went wrong, but I couldn't reproduce the defect, and still can't explain most.

Now that you've seen a potential problem, my advice would be to take some more controlled shots, from a tripod of a subject where there are no distance variables (the "traditional" brick wall shot comes to mind) and look for the same softness to the right side.If, after that, you still see a significant difference from left to right, then I'd say that a return of the lens is justified, and you can accompany it with documented proof.

Scott



bahadir

http://forums.dpreview.com/forums/re...ssage=25296694

You are not the first one reporting that. Follow what Scott suggest and see how well it goes. Actually I was giving the same advice like what Scott gave to the other fellow at dpreview


Daniel

mtngal Oct 23, 2007 10:23 PM

I'd agree - I have a similar problem with my DA 50-200, but I don't see it on every shot (and I didn't really notice it until it was way too late to do anything about it - seemed to get worse the longer I had it, or because I noticed it more as I became more experienced). Do some more tests, a brick wall or other flat surface and vary the distance, too. Good luck with it.

danielchtong Oct 23, 2007 10:33 PM

bahadir,

One thing I notice in your sample and that at dpreview as well. They both share the harsh lighting condition. Some people in dpreview refers that to decentering - or whatever it means.

Daniel

bahadir Oct 24, 2007 4:13 PM

snostorm wrote:
Quote:

Hi bahadir,

I can easily see the softness on the right in the full shot, but there are too many variables here to make a judgement from this one shot, IMO. Granted, a 17mm lens at f8 should give sufficient DOF to have just about everything in focus, but some other anomalous factor might be involved. I've seen too many shots that I've taken where something went wrong, but I couldn't reproduce the defect, and still can't explain most.

Now that you've seen a potential problem, my advice would be to take some more controlled shots, from a tripod of a subject where there are no distance variables (the "traditional" brick wall shot comes to mind) and look for the same softness to the right side.If, after that, you still see a significant difference from left to right, then I'd say that a return of the lens is justified, and you can accompany it with documented proof.

Scott
You really have keen eyes! I was not very sure if the softness I mentioned would be visible unlessI send100% crops. Actually, I tried many different ways to understand what was wrong! For example, I tried focusing on one point and then recomposed the view sliding that point to the right of the frame to seeif that's merely a matter of distance, but alas!The point I focused turned out to be the softest part:(Another interesting issue is that, this happens only at Landscape pictures:?I tried shooting a bookcase and then a large flat cushion with uniform pattern. To my surprise I could not detect a discernable difference between the left and right borders:!:

Upon readingthe valuablefeedbacksand the links generously provided here, I phoned the technical service of general distributor of Sigma in Istanbul,then packed up the lens and sent with UPS this afternoon! Now, I'm looking forward to receiving the replacement and will again share my experience with it : )



.................................................. ........................

Daniel wrote:



Quote:

bahadir

http://forums.dpreview.com/forums/re...ssage=25296694

You are not the first one reporting that. Follow what Scott suggest and see how well it goes. Actually I was giving the same advice like what Scott gave to the other fellow at dpreview

One thing I notice in your sample and that at dpreview as well. They both share the harsh lighting condition. Some people in dpreview refers that to decentering - or whatever it means.
Thank you Daniel! Well, I had noticed you were alsothere at dpreviews which I often visit : ) The link you providedperfectly displays my situation except I did not shoot at f/2.8tofeel evenmore unhappy!Consequently I packet and sent the lens by UPS under the influence of John Bean's repeated suggestion there: getting a replacement!Would love to share the results again here with you:cool:

.................................................. ............


mtngal wrote:

Quote:

I'd agree - I have a similar problem with my DA 50-200, but I don't see it on every shot (and I didn't really notice it until it was way too late to do anything about it - seemed to get worse the longer I had it, or because I noticed it more as I became more experienced). Do some more tests, a brick wall or other flat surface and vary the distance, too. Good luck with it.
I'm happy to hear you again : )According to mytestson bookcases, cushions and newspapers!! I saw that this partial softening effect happens at Landscape pictures only except @ 70mm end! I even tried focusing on sth on the left border of the frame by means of recomposing but the softness was there! The foliage and tilesare especiallyvery prone to that effect.

Anyway, in order toget rid of the stress ofhow my next shot would turn out to be, I posted the lens todayfor a replacement! I'mexpectingthe real Sigma performance I enjoyed at the 3/4 of the sightmy ex-lens covered!






kenyee Dec 22, 2007 8:38 PM

1 Attachment(s)
Thanks for posting an example of this. I think mine has the same issue. It seems to be a function of focal length and distance, so it doesn't show up in all photos, but when it does show up, it looks pretty bad as you can see...


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