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Old Oct 12, 2006, 10:14 PM   #1
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i was taking some photos yesterday afternoon (about 6:30 pm). I thought I had some decent light left. Was shooting in Aperture priority, f/2.8, shutter speed of 160, ISO 160, auto WB.

Most of the photos seemed to be front focused (see pic below). I was using the center point focus and was focused directly on my dogs neck. Took about 8 photos and they all look to be focused about 3-4 inches in front of my dog. Is this indicative of a lens problem or low light issues?

I've only had this lens 3 months. Do lenses require recalibration/repair? If so. where can i get this done? Would a Wolf Camera do this? Or do I need to send it directly to Sigma? I bought this lens at Beach Camera over the Internet.

Or maybe I'm just paranoid. Any helpful insight would be greatly appreciated. Thanks
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Old Oct 13, 2006, 5:34 AM   #2
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-> It's hard to tell from a picture of this size, but according to the grass blades below the dog it's difficult to see any front-focus...

The only good test for front/back focus is on a tripod at 45 degree to a ruler and in good light :idea:
(too many variables otherwise... even the AF mode can affect the outcome)
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Old Oct 13, 2006, 7:39 AM   #3
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Try the same photo with another lens to make sure the camera isn't having problems.
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Old Oct 13, 2006, 9:53 AM   #4
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NHL wrote:
Quote:
-> It's hard to tell from a picture of this size, but according to the grass blades below the dog it's difficult to see any front-focus...

The only good test for front/back focus is on a tripod at 45 degree to a ruler and in good light :idea:
(too many variables otherwise... even the AF mode can affect the outcome)
Sorry about the picture size, had to reduce it down quite a bit. I'm going to try the ruler test tonight. So this test should still be shot in Af mode or are you saying to eliminate that variable and use MF?When doing this test with the sigma 70-200 is there a preferred range I need to be in (70-200)? Thanks again.




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Old Oct 13, 2006, 9:53 AM   #5
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wsandman1 wrote:
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Try the same photo with another lens to make sure the camera is having problems.
Will do
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Old Oct 13, 2006, 3:27 PM   #6
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I meant tripod and one-shot AF i.e. don't use "servo" AF to prevent adding another variable...
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Old Oct 13, 2006, 5:43 PM   #7
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Okay, did some focus testing. Using two lenses (Sigma 70-200 f/2.8 and Canon 85 f/1.8). Placed a tape measure on the ground, camera facing downward at a 45° angle. The first photo was using the Sigma 70-200 @ f/2.8, 60 shutter speed, auto WB, iso 800. I was focused on the red 12" mark, center point focus, one shot AF. it's definitely better focused on the 11. All photos taken with tripod.


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Old Oct 13, 2006, 5:45 PM   #8
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This was with the Canon 85 f/1.8. Kinda hard to tell but it looks like the 11 is also in better focus.
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Old Oct 13, 2006, 5:48 PM   #9
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Looks to be a camera issue. Camera should still be under warranty i believe. Does this mean it has to go back to Canon direct? or are there typically service centers that will do the repair work if necessary?
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Old Oct 14, 2006, 5:51 AM   #10
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Excellent!
-> The camera does all the focusing Through-The-Lens ... Lenses are just passive elements

There's an eccentric stopping screw on the right side of the film chamber to adjust for this on most cameras (Nikon included). It set the position of the mirror at rest, hence the front/back focus:
FYI - http://www.astrosurf.org/buil/autofocus/adjust.htm
-> And a full description here: http://forums.dpreview.com/forums/re...ssage=19769329
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