Canon EOS 450D focusing problem

Discussion in 'Photography' started by MisterZenz, May 6, 2010.

  1. MisterZenz

    MisterZenz Guest

    Dear experts,

    I did some experimenting on my Canon 450D + Sigma 70-200 APO f/2.8
    combo. Too many images were not as sharp as they appeared on my
    focusing screen.

    Test results:
    http://www.kolesqueeste.nl/2010/05/05/canon-eos-450d-focusing-probleem
    - the text is in Dutch but the images know no language barriers ;-)

    Turns out that focusing goes wrong in normal mode: regardless of
    focusing method, auto or manual, the actual sharpness point on the
    image appears to be roughly 2cm in front of the point that appeared in
    focus in the viewfinder, but right in Live View mode: both manual and
    ContrastAF.

    Very frustrating.

    I've tested the Canon kit lens too and that had a similar (but less
    serious) offset. I figured the difference would come from the wider
    aperture and longer focal length of the Sigma (resulting in a smaller
    DoP and thus smaller tolerance).

    Just to clarify: when focusing, I judge sharpness on either the
    focusing screen or the Live View display. The actual sharpness of the
    resulting photo is judged on my monitor.

    If, while focusing, either by autofocus or manually, the image appears
    in focus on the focus screen, the sharpness point in the resulting
    photo (judged on my monitor) lies 1,5-2 cm in front of the focus point.

    If, while focusing, either by autofocus or manually, the image appears
    in focus on the Live View screen, the sharpness point in the resulting
    photo (judged on my monitor) lies exactly on the focus point.

    I double checked, by manually focusing on Live View and then switching
    to the view finder without touching the focus ring. Though less obvious
    (since the image cannot be enlarged, as on my monitor or on the Live
    View screen), the image in the view finder appears out of focus: the
    focus shifted to a point roughly 1cm behind the subject.

    My thoughts: viewing via the mirror (used by phase detection AF and/or
    manual focussing through the viewfinder) results in reading A. Viewing
    through the CMOS (Live View) results in reading B. Since the CMOS also
    produces the actual image, reading B, Live View, produces sharp photos.
    If A and B are not the same, I'm guessing the error would be in the
    mirror house. But that's maybe just because I'm an old fart, who
    understands physical stuff better than electronics ;-)

    Do any of you have a similar experience? If so, how did you solve it?

    Best regards,

    Zenz
     
    MisterZenz, May 6, 2010
    #1
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  2. MisterZenz

    RahQ5 Guest

    Just moving you up since you got buried in the other long thread.
     
    RahQ5, May 8, 2010
    #2
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  3. MisterZenz

    Ofnuts Guest

    No such problems with my 450D, but I've read that this kind of focusing
    happens, and is best fixed by taking the body *and lenses* to the repair
    shop to have them recalibrated under warranty.
     
    Ofnuts, May 8, 2010
    #3
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