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Thread: focus problem

  1. #1

    Default focus problem

    i used my 50mm on my friend's dslr.

    when i half-press the shutter release to focus, the view from the viewfinder is blur although the camera tells me focus is locked and good. then, when i press to shoot, the image came out to be good and in focus.

    i tried again, this time when the camera tells me focus is locked (although the view is still blur), i moved my body back abit til the subject in the viewfinder is sharp. i press the shutter to take the pic. this time the image recorded is blur, although the viewfinder is sharp.

    i tried manual focus. same thing, sharp in viewfinder, but when i shoot, the resultant image is blur.

    whats going on? back/front focus?
    when i use this lens on my own dslr, its good.
    my lens bad? or his cam bad?

    thanks guys

  2. #2
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    Default Re: focus problem

    Any dust, fogging or fungus inside the lens?
    Canon EOS 5D, 24-70 f/4 L IS, 50 f/1.2 L, 70-300 f/4-5.6 L IS, 600EX-RT. Sigma 12-24 f/4.5-5.6 EX.

  3. #3
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    Default Re: focus problem

    might be due to some changes in the diopter of the viewfinder

  4. #4

    Default Re: focus problem

    Quote Originally Posted by olsomica
    i used my 50mm on my friend's dslr.

    when i half-press the shutter release to focus, the view from the viewfinder is blur although the camera tells me focus is locked and good. then, when i press to shoot, the image came out to be good and in focus.

    i tried again, this time when the camera tells me focus is locked (although the view is still blur), i moved my body back abit til the subject in the viewfinder is sharp. i press the shutter to take the pic. this time the image recorded is blur, although the viewfinder is sharp.

    i tried manual focus. same thing, sharp in viewfinder, but when i shoot, the resultant image is blur.

    whats going on? back/front focus?
    when i use this lens on my own dslr, its good.
    my lens bad? or his cam bad?

    thanks guys
    Do the lines/grids/features (if any) on the focusing screen appear clear? If they are, then the calibration of the SLR may be out.

  5. #5
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    Default Re: focus problem

    the diopter has probably been moved to adjust for your friends eyes, does he wear glasses? if not it may have been moved by accident

  6. #6
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    Default Re: focus problem

    Confirm dioptre adjustments.

  7. #7

    Default Re: focus problem

    Quote Originally Posted by espn
    Confirm dioptre adjustments.
    But manual focus can become sharp leh? If diopter wrong, I don't think it will become sharp at all.

  8. #8
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    Default Re: focus problem

    Quote Originally Posted by lsisaxon
    But manual focus can become sharp leh? If diopter wrong, I don't think it will become sharp at all.
    Yes PRO!!!

  9. #9

    Default Re: focus problem

    Quote Originally Posted by espn
    Yes PRO!!!
    Walao.. mai suan lah.. Just an opinion only leh... I may be wrong..

  10. #10
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    Default Re: focus problem

    Quote Originally Posted by lsisaxon
    Walao.. mai suan lah.. Just an opinion only leh... I may be wrong..
    I also ma.. opinion nia... newbie lah... don't take it to heart, just joshing ar'd

  11. #11
    Moderator catchlights's Avatar
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    Default Re: focus problem

    just adjust diopter will do. nothing to do with any other thing.

  12. #12

    Default Re: focus problem

    confirm not diopter
    adjusted max bothways still like that

  13. #13

    Default Re: focus problem

    Quote Originally Posted by espn
    I also ma.. opinion nia... newbie lah... don't take it to heart, just joshing ar'd
    Dunno leh.. if my diopter wrong, image will never be sharp however I focus one leh..
    Last edited by lsisaxon; 26th February 2006 at 07:47 PM.

  14. #14

    Default Re: focus problem

    Quote Originally Posted by lsisaxon
    But manual focus can become sharp leh? If diopter wrong, I don't think it will become sharp at all.
    true true

  15. #15
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    Default Re: focus problem

    he where got say mf is sharp?
    Quote Originally Posted by olsomica

    i tried manual focus. same thing, sharp in viewfinder, but when i shoot, the resultant image is blur.

  16. #16

    Default Re: focus problem

    Quote Originally Posted by olsomica
    true true
    Which camera body is that? Can you try something? Use AF, focus on a marking on a ruler placed 45 degrees, then see if the focus on the viewfinder is in front or behind the AF point.
    Last edited by lsisaxon; 26th February 2006 at 08:32 PM.

  17. #17
    Moderator catchlights's Avatar
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    Default Re: focus problem

    Quote Originally Posted by olsomica
    confirm not diopter
    adjusted max bothways still like that
    should be somewhere in between.


    Quote Originally Posted by olsomica
    i used my 50mm on my friend's dslr.

    when i half-press the shutter release to focus, the view from the viewfinder is blur although the camera tells me focus is locked and good. then, when i press to shoot, the image came out to be good and in focus.

    i tried again, this time when the camera tells me focus is locked (although the view is still blur), i moved my body back abit til the subject in the viewfinder is sharp. i press the shutter to take the pic. this time the image recorded is blur, although the viewfinder is sharp.

    i tried manual focus. same thing, sharp in viewfinder, but when i shoot, the resultant image is blur.

    whats going on? back/front focus?
    when i use this lens on my own dslr, its good.
    my lens bad? or his cam bad?

    thanks guys
    Common sense will tell your that nothing wrong with the lens, and the camera focusing system, just only the dioptre adjustments, or your friend modified it for his/her eye only.

  18. #18
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    Default Re: focus problem

    Quote Originally Posted by catchlights
    should be somewhere in between.



    Common sense will tell your that nothing wrong with the lens, and the camera focusing system, just only the dioptre adjustments, or your friend modified it for his/her eye only.

  19. #19

    Default Re: focus problem

    Quote Originally Posted by espn
    Taking D70 as an example, there are 2 screws you can turn for adjusting the mirror stop position. One of them adjusts the stopper for the mirror for the AF sensor and the other adjusts the stopper for the mirror to the focusing screen. A possibility is that either the mirror is jammed or it wasn't calibrated correctly.

    The D70 which my previous company bought has both alignment slightly off. By shooting a 45 degree ruler, I was able to see that what was focused by the AF sensor, the focusing screen and the CCD are off by a bit.

    Using a microscrope (previous company was dealing with semiconductors), I was able to precisely calibrate the optical distances of the AF sensor, focusing screen and the CCD sensor by using the 2 stopper screws. And it does make quite a difference on the focusing accuracy.

  20. #20

    Default Re: focus problem

    Quote Originally Posted by roti_prata
    he where got say mf is sharp?
    Let me rephrase that.. If diopter is wrong, the viewfinder image can never be sharp. But he was able to focus and obtain a sharp image in the viewfinder, which means that the diopter should be correct. However, getting the image sharp in the viewfinder did not yield a sharp image in the sensor, which also means that the distance from the lens mounting flange to the focusing screen is not the same as the distance from the lens mounting flange to the sensor. If it were really the diopter, everything else in the viewfinder would not be sharp also.
    Last edited by lsisaxon; 26th February 2006 at 10:26 PM.

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