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Old Nov 17, 2003, 11:23 AM   #1
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Default Focus problem with Canon EOS-10D

I have recently bought a new Canon EOS-10D and a new Sigma EX 17-35 f2.8-4 HSM lens. My problem is that I get severe front focus problem when I use it at wide(17-25 mm). I have estimated this front focus to be around 1-1,5 feet when the focus distance is 4-5 feet. The aperture is f2.8, only the center AF mark is selected, a tripod is used, the subject has good contrast, well lit etc..

If I focus on the subject at tele (30-35 mm) lock the focus and then shift the zoom to wide, the pictures are perfectly sharp.


The problem is constant, it is not coming and going.


Can anyone help me to locate the problem. Is it the Sigma lens, the camera (I have read that some 10D's have a AF focus problem) or is it a compability problem?
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Old Nov 20, 2003, 6:43 AM   #2
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I had a similar problem with my Sigma 70-200 f2.8. The only things people could think of is when I was in the 6-10 foot range of the subject shooting at 2.8 causing around in some cases 1/4th of an inch of DOF. If it was to front or back focus it could make it come out blurry. Here are some samples of images that this has happen.





Not sure if your images look like that, but thats what most of mine look like at 2.8

I don't have that lens anymore...
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Old Nov 20, 2003, 3:46 PM   #3
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Default Re: Focus problem with Canon EOS-10D

Quote:
Originally Posted by frederiksen
My problem is that I get severe front focus problem when I use it at wide(17-25 mm).
Try the focusing tests on this site:

http://www.photo.net/learn/focustest/

-jb
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Old Nov 20, 2003, 4:14 PM   #4
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this probably sounds stupid, but what is "front" and "back" focus?

I've seen this used quite a bit here, but can't find a definition.

Thanks!
Jim
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Old Nov 20, 2003, 5:01 PM   #5
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It's when you use AF to focus on a given point in space, and the camera claims it's in focus.... but when you look at the pictures a region either behind (back focus) or in front (front focus) is actually in focus and the location where you put the AF point isn't in focus.

The thing to remember is that the 10D only says that the focus point will be somewhere in the DOF. Unlike the 1D or 1Ds, where it guarrenties that its within the middle 1/3 (Or 2/3? I forget. I know they have guarrenties about where the focus point is within the DOF.) What I am more sure about is that the better cameras don't allow the point in focus to be on one of the edges of the DOF.

What this means is that if you point the focus point at a person's nose, it is actually legal to have just the tip of the nose in focus and the rest of the head out of focus. That is not a front focus problem. I'ts annoying and sucky and I dislike it a lot... but it's perfectly legal with the 10D. A 1D or 1Ds wouldn't do that. Probably the only reason why I would like a 1D or 1Ds, their AF system is much better.

Eric
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Old Nov 20, 2003, 6:46 PM   #6
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frederiksen

This could be your problem here:
Quote:
If I focus on the subject at tele (30-35 mm) lock the focus and then shift the zoom to wide, the pictures are perfectly sharp.
... but I can't recall this ever happened on both my Sigma EX 17-35mm f/2.8-4 HSM or EX 70-200mm f/2.8.

The problem is actually most accute on my EF 28-135mm f/3.5-5.6 IS USM, ie once it's in focus you can not zoom the lens in or out or the focus will change because of its varifocal design (look for that warning in the Canon lens manual)! I've got some of the best landscape shot from my Sigma EX 17-35mm f/2.8-4 HSM as well as other folks: http://www.belgiumdigital.com/albums..._albumpage.htm



UniSonBBS

I can't help to notice from the exif that you were shooting 1/180s @ 200mm where camera shake could be problem too if that lens was not on a tripod especially with a 1.6x factor (and @ close range). This is what I get up close @ 1/500s f/2.8 @ 200mm from the same Sigma EX 70-200mm f/2.8!
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Old Dec 2, 2003, 10:01 PM   #7
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Default Re: Focus problem with Canon EOS-10D

I had the exact same problem. In fact my Sigma 17-35 is now in New York awaiting their pleasure along with a Sigma 28-80 with the same problem while my Sigma 70-300 has no problem but my new Sigma 24-135 F2.8 also has the problem but only at 24mm.

The problem is the "Front Focus" problem. I define it as a dramatic shift in focus point to about 1/3 the distance in front of whatever you are focusing at. At 30 feet, the camera/lens will focus at 20 to 15 feet from the camera instead of 30 feet under the following conditions:

- Wide open (like F2.8)
- Wide angle lenses only at their maximum wide setting
(17, 20, 24, 28 and to a lesser extent 35 mm)
- Ruler test usually also fails
- Usually non-Canon lenses such as Sigma and Tamron (not sure about Tokina, Tamron 19-35 is actually ok!)

All tests were done on a tripod with a shutter release, center AF point registered. Notice the focus problem may exist to a lesser degree at higher F-stops but with increased depth of field most people don't seem to notice the problem. Case in point, Non L Canon lenses start out at F3.5 where the problem doesn't seem to show much. No wonder Canon lenses work - They are so slow they start out with good depth of field to hide any sharpness problem.

The Canon people in the US and the International division in Japan have written me declaring that they make no claim that their lenses will work with ANY third party lens. Canon dealers have also been sent letters to this same effect. It reminds me of the early days of Apple just before they almost went down the tubes in trying to force their customers to use only their equipment. Only now Apple is recovering from that decision. I can only hope Canon becomes more open minded.

The third party lens people say the camera is at fault and the camera people say the third party lens people don't know their secret data communications protocol between body and lens (maybet this will be another Microsoft trust case). Meanwhile unless I ship my camera body back to Canon for a month or so, I'm out of business.

I'm planning to look at a Rebel and test these lenses against the Rebel. If they work I'll probably have to buy a Rebel to have something while my Canon 10d is in the shop being fixed for a problem they say I don't have.
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Old Dec 3, 2003, 9:31 AM   #8
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See here:

http://www.stevesforums.com/phpBB2/v...?p=81719#81719
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