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12-29-2009, 04:46 PM   #1
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Sigma 10-20mm Focus Issue?

Looks like I have an issue with my Sigma 10-20mm f/4-5.6. I am looking for well considered opinions. I am happy to answer questions about my technique, etc., but I will tell you up front that I tested all my lenses and this is the only one that showed this issue.

The issue seems to be that on the left side of the focus chart, the focus is dead on. On the right side of the focus chart, it looks to be shifted to the rear... back focusing really. I'd like your opinion of what this is.

Here is a wider view of the focus chart for reference. For this purpose it does not show enough, so bear with me. At this level it almost looks OK.



If you look closer, per the below picture, you can see the text on the left is sharp and the text on the right is not. Further you can see that the oof portions start at different places on the left versus the right. It looks like the left comes into focus at about 14mm in front of the text, and on the right it doesn't seem to start to be in focus until 6mm BEHIND the text. Compare the 30mm and 40mm behind the text. on the left, oof, on the right still in focus. The more you look, the more it seems like there is actually a pretty serious issue with this lens.

I was very careful about the test. The lens was centered, and it was right at 45 degrees. The exif should be intact, so have a look.



Thanks in advance for any opinions. The lens is under warranty, so if the recommendation is send it in, I won't have any issues there. Seems like the right thing to do. I had a soft Sigma once before and the service did it a world of good.

Thanks in advance for your considered opinions.

woof!

12-30-2009, 06:17 AM   #2
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Tamron for Comparison

Here is my Tamron 28-75mm for the sake of comparison.

12-30-2009, 06:28 AM   #3
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The two last pictures only show "Content protected by owner".
12-30-2009, 06:30 AM   #4
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Your second and 3rd shots are locked and we can't see them. Just looking at the top shot you could be looking at a lens that is slightly off center or the focus plane is not perfectly parallel to the sensor. But the copy I had showed softness in the corners while very sharp in the center. It could simply be that one side is showing this softness.

It's a very nice lens but IMO not equal to the Pentax 12-24mm in terms of across the frame sharpness. But with the huge DOF of an ultra wide, it's really not a big issue unless shot at 10mm and wide open.

12-30-2009, 07:46 AM   #5
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QuoteOriginally posted by Asahiflex Quote
The two last pictures only show "Content protected by owner".
Fixed. Sorry, but thanks for your input...

Seaain
12-30-2009, 07:53 AM   #6
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Looks ok to me.
And you're very lucky w/ that 28-75. I returned 3 copies because none of them focused like that when I tested at 28/50/75 focal lengths :-P
12-31-2009, 08:43 AM   #7
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QuoteOriginally posted by kenyee Quote
...you're very lucky w/ that 28-75. I returned 3 copies because none of them focused like that when I tested at 28/50/75 focal lengths :-P
I AM lucky with the Tamron... BUT it had a lazy iris when I purchased it and had to be sent back. Tamron did an exceedingly great job of calibrating the lens while they were fixing the aperture.

I think that the Tamron photo shows pretty clearly though, when compared to the detail shot from the 10-20mm, that the 10-20mm is really quite soft on the right side, and in fact the plane of focus appears to be shifted significantly rearward ONLY on the right. The left looks dead-on.

I sent it in. 4 year warranty on that lens. I never registered the lens, but they did not seem concerned about that. I'll report back what happens.

woof!
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