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Old Sep 17, 2005, 9:33 PM   #1
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This picture was taken with a Canon EOS 20D with a Sigma 70-300mm DG lens set at 200mm. The camera was on a tripod with the mirror lock option selected and used a remote trigger release to avoid camera shake. Several pictures were taken at different zoom settings with the same results. Resolution was set at the highest value with least compression. This is a 100% crop to best exhibit the problem I see. No other post processing was done. I was about 40 feet from the item, outside and cloudy. Settings were f5, 1/100s, ISO200.

There is a blur on top and right of all letters. The bottom and left sides seem to be much sharper. I also have the Canon EFS 17-85mm IS lens which does not exhibit the same problem. All letters are sharp.

Is this normal for this Sigma lens or should I expect better results?

How do you like my subject?? :-)

Thank you

Arvid

EDIT - My host must have turned off my ability to link pictures - Hope this one works.

Thank you, Peter, for your help.

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Old Sep 17, 2005, 10:43 PM   #2
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No Image seems to be attached :G

But no, a blur is not normal, especially only on one side of letters.
Seeing the image may help see what it is.

Peter.
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Old Sep 17, 2005, 10:53 PM   #3
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Peter, I am not sure why the image doesn't show. I used the "insert image" icon. I'll post the address - http://ourmnacres.us/pics/Sigma.jpg

Yes, I am alittle worried that this lens is either defective or it might be normal. Either way is bad. It is a new lens.

Thanks

Arvid
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Old Sep 17, 2005, 11:07 PM   #4
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I think
Code:
http://ourmnacres.us/pics/Sigma.jpg
is the problem, if I hit it I get redirected to
Code:
http://www.100webspace.com/
Maybe they do not allow image linking.

EDIT: Yup that is it, I can view it if I enter the URL manually into the browser.
And ya, that does look like an odd distortion, it should not normally happen.
But I am not sure what it is.
Have not seen that before, ocurring on only one side of text.

Peter.
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Old Sep 18, 2005, 11:49 AM   #5
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Ah great you moved it to a site that allows image linking!

After thinking a bit the image is probably actually bluring on both sides of the text.
It is the direction that threw me off. The light into dark you can see easily, but on the other edge if the blur direction is the same it is light over light so would not be visible.

Looks almost like a halo effects filter.
Is there maybe a smudge on a lens element, maybe on an inside element?

Peter.

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Old Sep 18, 2005, 3:06 PM   #6
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Manyyears ago with my Contax RTS film camera and a newSun tele-macro Inoticed similar problems. I came to the conclusion it was internal fogging ... going from the airconditioned environment directly outside on a muggy day. If I let the lens warm up, the problem disappeared. I sentthe lensback and the replacement did not exhibit the problem ... I suspect there was moist air trapped between the lens elements. I have noticed similar problems with several consumer digital cameras I own ... and avoid it by allowing the camera to either warm up or cool down to ambient temperatures. I even allow my various slr lenses to acclimate before using them.
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Old Sep 18, 2005, 5:56 PM   #7
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That is a very good point about moisture in the lens. I was unable to totally duplicate the problem today although, I think I may have found part of my problem. I was relying on auto focus. It appears that auto focus does not always do a good job. When I manually focus, all letters are clear. If I manually turn the focus ring one direction, the auto focus will bring it back to good focus. However, when I manually turn the focus ring the other direction, the auto focus does not bring it back to true focus. This seems to be consistent.

When I used a 10" x 12" white card with vertical and horizontal lines, the lens focused properly every time. I will have to experiment under different conditions and see what happens.

Thanks for your comments

Arvid
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