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Old Sep 5, 2006, 6:33 PM   #1
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Today I received my 24-105 f/4 L and am impressed with the image quality but not too impressed with the focusing. When I focus on an objet at the lower end of the zoom range, then zoom in at 100%, it's clear (no pun intended) that the focus is not accurate.

If I zoom in and focus, all is fine. My 28-135mm IS lens and 70-200 f/2.8 lenses do not do this - they are sharp as a tack on the focus regardless of the zoom setting.

Any thoughts? I've read that some of these may have focus calibration issues. Is this an example of this problem?

Thanks,

Gary
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Old Sep 5, 2006, 11:06 PM   #2
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On the 70-200 f/2.8 I can understand because it's a parafocal design...
The 28-135mm on the other hand is a varifocal meaning the focus will change as the zoom varies (it's lens manual even warns against zooming after focus). IMO you're seeing the same varifocal effect on the 24-105 f/4 because of its similar design
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Old Sep 6, 2006, 11:49 AM   #3
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Thanks for the info.One thing though. When I zoomed in on the 24mm shot on my PC, it was not as focused as the same shot at 105mm. Using the camera zoom to compare is not a good comparison according to your posting but shouldn't zooming on the actual photo tell me something?

I did a comparision with the 28-135 and it appears that both are doing this - not as in focus at wider angles. It's just that the 24-105 was more pronounced at first. It may have had something to do with the lighting at the time as well. I'll keep experimenting with it.

Gary
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Old Sep 21, 2006, 3:47 PM   #4
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