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Thread: Depth of Field question

  1. #1
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    Default Depth of Field question

    How do you maintain similar depth of field across different focal lengths? I'm currently under the assumption that if you have the same f-stop, and same distance to the subject, the depth of field should be the same, even if you change focal length. Is this correct?

  2. #2
    ...formerly known as 'drapeama' Marc-Alexandre Drapeau's Avatar
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    I'm not an expert, but I guess if you don't change the aperture, it should stay similar. With my Vivitar lens (70-150 -f/3.8) if I'd take 2 pictures (one at 70mm and the other at 150mm) I guess they would be pretty similar in depth of field. I'd say that only the perspective would be different, which would probably affect the depth.
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    Legend Almohada's Avatar
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    DOF is affected by camera-subject distance, aperture and focal length. If you change the focal length, you will have different DOF. You gotta open up or close your aperture and then change your shutter speed accordingly to maintain the same exposure.
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    Legend Bif's Avatar
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    If you change nothing but the focal length of the lens, the "zone of acceptable sharpness" or depth of field will remain pretty much the same. However at wide angle settings that "zone" will appear compressed because spatial relationships appear different from telephoto.

    You will have an expanded field of view and while a "zone" of 5 feet will still be 5 feet deep at either wide angle or telephoto, it will appear different in the picture because of spatial relationships of items in the field of view. With a wide angle that zone will appear to be smaller because everything in the frame will appear smaller.

    When it comes to comparing DOF at different focal lengths one needs to remember:

    The visual effect of shallow focus (shallow zone of acceptable focus) is enhanced by the following:

    Longer focal length lens.
    Closer focusing distance.
    Longer distance from subject to background elements.
    Wider aperture.

    The visual effect of deep focus (deep zone of acceptable sharpness) is enhanced by the following:

    Shorter focal length lens.
    Longer focusing distance (camera to subject).
    Shorter distance from subject to background elements.
    Smaller aperture.

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    That answers my question quite thoroughly. Thank you.

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    Senior Member redfalcon's Avatar
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    And very well said too, Bif.

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    Legend Bif's Avatar
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    Thanks.

    That came from a tutorial presentation I gave our local photo club a few months ago. Some of the new members requested something for beginners so I put together a few (basic dslr controls, and aperture priority use) with images to illustrate.

    We've got a pretty good club here, I'm a retired professional still photographer and enjoy helping others out. I became a club member to remain connected with folks with similar interests.

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    Have you ever considered putting the information online to share?

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    Tropical Legend cgbier's Avatar
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  10. #10
    ...formerly known as 'drapeama' Marc-Alexandre Drapeau's Avatar
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    Maybe this would help:


    Also this one:
    Last edited by Marc-Alexandre Drapeau; 2012 April 20th at 14:56.
    I DO IT BECAUSE I CAN. I CAN BECAUSE I WANT TO. I WANT TO BECAUSE YOU SAID I COULDN'T.

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    Just watched the videos. That guy has a great presentation.

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    ...formerly known as 'drapeama' Marc-Alexandre Drapeau's Avatar
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    Quote Originally Posted by Bertzie View Post
    Just watched the videos. That guy has a great presentation.
    Yep. He also has some nice reviews on some cheap gear too. The RJ follow focus did impressed me in fact.
    I DO IT BECAUSE I CAN. I CAN BECAUSE I WANT TO. I WANT TO BECAUSE YOU SAID I COULDN'T.

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