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Old 5th of February 2007 (Mon)   #1
pythagpython
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Default Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Hey guys,

I decided to get a Sigma 17-70mm to replace my Canon 17-85. It turns out that it isn't so much of a party as it should be. A little background:

I have had the Canon 17-85 for a little over a month now and want to get rid of it because of horrific distortion, CA and OK picture quality. This is especially since most of my photos are taken at 17mm.

So I got the Sigma 17-70 today and was really excited, but when I tested it out, it has been giving me some stress. Pictures taken at 70mm look really bad, as if they are out of focus. It looks like there is some "shadowing". Is there something wrong with it? Please help me out.

Here are some examples:

Sigma @70/4.5

s45.jpg

Canon @ 70/5.6

c56.jpg
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Old 5th of February 2007 (Mon)   #2
pythagpython
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Here is another (worse) case of this:

Sigma @70/4.5
s245.jpg

Canon @ 70/5.6
cv56.jpg
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Old 5th of February 2007 (Mon)   #3
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Bump, any suggestions?
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Old 5th of February 2007 (Mon)   #4
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Exif data? Presume tripod used? If slow shutter speed it could be the IS helping the Canon look better. You Might want to try a focus test that's more precise/standardized such as described here http://focustestchart.com/chart.html
Some also use three AA batteries lined up 3/4'' apart focusing on the middle one.

I guess in the end if it really is off you need to return it if new or repair it if used.

Good luck.
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Old 5th of February 2007 (Mon)   #5
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Are the photos cropped?
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Old 5th of February 2007 (Mon)   #6
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

The photos are cropped 100%, taken on a tripod with remote.
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Old 5th of February 2007 (Mon)   #7
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Oh, and IS was turned OFF on the tripod for the canon.
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Old 5th of February 2007 (Mon)   #8
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Ok, did the focus chart and it is misfocusing. I think I will have to send it back. What do you guys think? I just wish that I could be loving this lens.
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File Type: jpg fc.jpg (71.5 KB, 623 views)
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Old 5th of February 2007 (Mon)   #9
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

This is as opposed to the canon, which apparently focuses fine. Sigh... what awful luck...
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Old 5th of February 2007 (Mon)   #10
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Ok, so what do you call this? Back focusing? This really stings Sigma's reputation in my mind. I mean, really, what are the chances that my first Sigma lens will have a defect!? Should I give them another try?

Oh yeah, both were taken on tripods, 100% crop.
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Last edited by pythagpython : 5th of February 2007 (Mon) at 23:32.
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Old 6th of February 2007 (Tue)   #11
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

I had exactly the same thing with my first copy of this lens. The second one is better (although I don't think it's perfect).
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Old 6th of February 2007 (Tue)   #12
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

f/4.5 @70mm on this lens is wide open for that extension. Try reshooting the focusing chart at f/5.6 and then f/8.
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Old 6th of February 2007 (Tue)   #13
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Bah looks like im back focusing big time. Now the question is, where do you send it to get repaired?
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Old 6th of February 2007 (Tue)   #14
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Quote:
Originally Posted by Ospi View Post
Bah looks like im back focusing big time. Now the question is, where do you send it to get repaired?
It seems like this is a common problem with this lens. WTF is wrong with Sigma's QC?! I think I'm going to send it in for a replacement.
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Old 6th of February 2007 (Tue)   #15
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Default Re: Replacing Canon 17-85 with Sigma 17-70, but is it misfocusing?

Quote:
Originally Posted by pythagpython View Post
It seems like this is a common problem with this lens. WTF is wrong with Sigma's QC?! I think I'm going to send it in for a replacement.
Yeah QC does seem to be a bit of a problem, then again i think they would rather risk not being as precise with their lenses in order to make them cheaper and rollout faster and take the hit with the 5% odd focusing problem.

though when i spend $400 i like to think its going to arrive 100% perfect.
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