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Thread: Is cropping of digital pics considered "cheating"?

  1. #21
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    Originally posted by tsdh
    Don't worry, Jed is not around.
    Not around? I don't know about that. But if this keeps up, I'm going to be forced out of here.

  2. #22

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    OK I'll stop with the Jed cracks.... Promise!

  3. #23

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    Originally posted by ckiang
    If you take a shot using a 35mm lens, and crop a 50mm equivalent out of it, DoF is that of a 35mm lens.
    Depends on your reproduction ratio. If you have to enlarge it more (due to the crop), I would expect the DOF to be less.
    (void *) &NHY;

  4. #24
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    Originally posted by nhyone


    Depends on your reproduction ratio. If you have to enlarge it more (due to the crop), I would expect the DOF to be less.
    Why would that be so? DoF is never dependent on reproduction ratio. DoF of a shot taken with a 35mm will be that of a 35mm regardless of whether the final print is 4R, 8R or even 20x30.

    Btw, talking about post-shot cropping here, as in, cropping in the darkroom or PC.

    Regards
    CK

  5. #25
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    Originally posted by Jed
    Not around? I don't know about that. But if this keeps up, I'm going to be forced out of here.
    Are you offended?
    Don't keep everything too serious like "old-men club", or else friction will easily ignite as recently happen in another local photography-forum.

    Keep smiling Jed, and keep posting here. I learn from you too.
    Remember your post on another thread regarding 'infinity-focus' at long-tele? that's great, I never realise it until I read your post.

  6. #26
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    Originally posted by ckiang
    Why would that be so? DoF is never dependent on reproduction ratio. DoF of a shot taken with a 35mm will be that of a 35mm regardless of whether the final print is 4R, 8R or even 20x30.
    CK, I think nhyone has a point. The size of the final print you want will directly influence the maximum acceptable circle of confusion size, and thus in a sense influence DOF. As such, a significant smaller print may well yield a greater "acceptable" DOF for the same negative. Don't forget, how we perceive the "depth" in DOF is ultimately pretty subjective, and largely dependent on the print size and viewing distance.

  7. #27
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    Originally posted by Midnight
    CK, I think nhyone has a point. The size of the final print you want will directly influence the maximum acceptable circle of confusion size, and thus in a sense influence DOF. As such, a significant smaller print may well yield a greater "acceptable" DOF for the same negative. Don't forget, how we perceive the "depth" in DOF is ultimately pretty subjective, and largely dependent on the print size and viewing distance.
    If I didn't remember wrongly, Circle of Confusion and final print size are not related as well. It only affects the acceptable DoF on the film itself.

    Regards
    CK

  8. #28
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    Originally posted by tsdh
    Are you offended?
    I don't know. What do you think.

    *Big grin*

    Bye.

  9. #29

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    well, I have no problem with minimal cropping. However one must know that cropping excessively also reduces the quality of the image. If you can train cropping with your eyes while shooting, then you won't need to crop while printing at all. This can ensure that you won't need to spend countless hours in the darkroom trying to get things right. It's unproductive.

    Maybe you can consider me a purist. But I think composition plays an important part in photography. If you do not have an aptitute or acquired taste of good composition, you defeat the purpose of doing photography.

  10. #30

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    Originally posted by ckiang
    If I didn't remember wrongly, Circle of Confusion and final print size are not related as well. It only affects the acceptable DoF on the film itself.
    Yes, for a given film size, it is generally assumed that the reproduction ratio will not affect the DOF, because the viewing distance increase.

    However, circle of confusion is based on how much enlargement is required for the normal print size and "normal" viewing distance.

    Cropping means you are in effect using a smaller film format. You will need to enlarge more to get the standard print size.

    One formula for CoC I saw uses the film diagonal divided by a constant.
    (void *) &NHY;

  11. #31
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    Originally posted by nhyone
    Yes, for a given film size, it is generally assumed that the reproduction ratio will not affect the DOF, because the viewing distance increase.
    However, circle of confusion is based on how much enlargement is required for the normal print size and "normal" viewing distance.
    Cropping means you are in effect using a smaller film format. You will need to enlarge more to get the standard print size.
    You have a point by saying that DOF will be narrower for that cropped image. Yes, that is true. But you have to take note that the reduction of DOF in the cropped image still can't be as narrow as the DOF of the long lens (to achieve the same magnification). It is negligible as compared to the reduction of DOF vs focal length.

    Following is an image taken from 'The Photographer's Handbook', demonstrating the difference of zooming by cropping, and zooming by using long-tele lens.
    The first picture shows a full frame taken with 40mm lens using 6x6 film format. And the rectangles inside the picture show the respective crop if longer focal length is in use.


    The following pictures show the difference. The left picture is an enlarged crop of the one taken with 40mm lens, while the right side picture is a full frame taken with 500mm lens from the same distance at same aperture (all pictures were exposed at f/11 )


    We can see that the cropped image has wider DOF than the one using long-tele, altough more grainy.
    Last edited by tsdh; 18th July 2003 at 02:23 PM.

  12. #32

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    Originally posted by tsdh
    But you have to take note that the reduction of DOF in the cropped image still can't be as narrow as the DOF of the long lens (to achieve the same magnification). It is negligible as compared to the reduction of DOF vs focal length.
    A picture is worth a thousand words!

    This shows why a 50mm lens on a D60, despite being equivalent of a 80mm lens, has more DOF than a real 80mm lens.

    This shows also why digital compact cameras, with their short focal length lenses, have much more DOF.
    Last edited by nhyone; 30th August 2002 at 02:31 PM.
    (void *) &NHY;

  13. #33
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    To confuse the discussion even further , here is an article on DOF which is very interesting reading.

    http://www.luminous-landscape.com/tutorials/dof2.shtml

  14. #34

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    Originally posted by Darren
    To confuse the discussion even further , here is an article on DOF which is very interesting reading.
    I read this article before, although I have totally forgotten about it.

    I don't know if what he presented is true or not, since he only gave empirical evidence. However, no one seemed to have pointed out his flaws, if any.

    In any case, it may be confusing, but there is no contradiction. See carefully which are the variables and which are the constants.
    (void *) &NHY;

  15. #35
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    Originally posted by nhyone
    I don't know if what he presented is true or not, since he only gave empirical evidence. However, no one seemed to have pointed out his flaws, if any.
    In any case, it may be confusing, but there is no contradiction. See carefully which are the variables and which are the constants.
    What he presented is true. And you're right, see the variables carefully. DOF will be constant for all focal length, if you can keep the object size the same by altering camera-to-object distance.
    So the variables are; distance & focal length. Image size & aperture are kept constant.
    While in our discussion above, the variables are: focal length & image size. Distance & aperture are kept constant.

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