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Old Aug 6, 2006, 7:47 PM   #1
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I'm having focus issues - I can get super sharp focus if what I want in focus fills the frame. If I attempt to focus on a piece of what fills the frame it's not in focus.

Here's a link to a thread I started on another forum that explains what my issue is and has sample photos - also there have already been questions and suggestions made that haven't helped me.


If anyone has any suggestions - I'd very much appreciate it - I'm ready to throw this camera out the window! Thanks in advance for any help. Brooke

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Old Aug 6, 2006, 8:06 PM   #2
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This is your main problem IMO:
"I played a bit this morning some more and I seem to have better luck with focus from a distance if I zoom in and focus then hold the focus and zoom out. I know I know thi is not the way to do it - and no it's not giving me consistent results - it also limits how far away I can be."

Most if not all Canon zooms are varifocal in design -> i.e. they won't hold focus as the focal lenght is changed! Zoom and compose 1st before locking in focus and shoot...

-> What you need are parafocal lenses Sigma and especially Tokina make theses zooms which will hold focus as the zoom is changed: http://www.fredmiranda.com/reviews/s...hp?product=176

"... is what is commonly referred to as a parafocal lens, meaning when focus is achieved at a telephoto focal length, it is possible to zoom back to a wide angle and maintain focus on the subject."
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Old Aug 6, 2006, 10:04 PM   #3
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The research that I did said that the Canon 24-70 2.8L is a parfocal lens. And that would explain whyI am gettingbetter focus when I focus andzoom back than when I rely on the camera to focus when I amzoomed back.

I'll look and see if I can find the link that indicated that this lens is a parfocal lens.

Found one of them:

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Old Aug 7, 2006, 2:04 AM   #4
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It's difficult to tell from such low resolution shots, but it seems like your camera isn't focussing properly.

If it's new enough take it back and get a replacement. Otherwise it should go in for a calibration service - send your lens along and ask them to calibrate the lens and body together.

At the very least go back to the shop - take along your lens and CF card and ask them if you can test another XT. When you get home if the pics are OK then you know you have a camera problem.
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Old Aug 7, 2006, 10:46 PM   #5
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Have you done any focus tests with your camera and different lenses?

Also, do you have any filters on this lens while having this problem?

It appears that you have a backfocus issue here. I have read that the Canon 24-70L sometimes has a backfocus at a wider angle. You can check this by doing a focus test with either a ruler, objects set at different distances, a focus sheet a an angle, and with different lenses.

Try doing these tests at different apertures, from a tripod with a cable release.

If you find that your lens is out, you can send it to Canon for calibration. I would also send the camera and have them check both. The camera can cause this too.


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