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Thread: Depth of Field Calculator Problems

  1. #1
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    Dec 2008
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    Depth of Field Calculator Problems

    Hi!

    I was reading the DOF and Hyperfocal distance tutorial. They are well written articles. Then I used the DOF calculator and compared DOF for senso formats - 35 mm, CF 1.5x and FourThirds sensors. What surprised me was that the DOF was smaller for smaller sensor sizes. Now this is what I have not observed in use and even in contrary to many articles I have read.

    For example- If I shoot portrait using a Point and shoot d-camera @f/2.8, focal length 85 mm (35 mm equivalent) and then shoot the same subject using Full frame DSLR with 85 mm @f/2.8, the subject in the later case is much more isolated from Back ground than when using PnS camera.

    Please help clear this confusion

    Thanks,
    Xtack

  2. #2

    Join Date
    May 2008
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    Re: Depth of Field

    Check out the calculator again; you have to input the actual focal length for each sensor size, not the equivalent focal length.

    The smaller the sensor, the shorter the focal length for an equivalent field of view.
    Last edited by rc53; 26th December 2008 at 09:07 PM.

  3. #3

    Join Date
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    Have a guess :)

    Re: Depth of Field

    Hi Xtack,

    I think that you must have made a mistake somewhere along the way. If you haven't already, have a read of the Digital Sensor Sizes Tutorial http://www.cambridgeincolour.com/tut...ensor-size.htm

    Using the DoF comparison calculator for an 85mm lens @ F2.8 on a crop-factor and full frame cameras it tells us that on a full frame camera you'd need a 136mm lens to get the same field of view, but you'd only need an aperture of 4.5 to get the same DoF - in other words, if you also selected an aperture of 2.8 on the full frame camera, the DoF would then be less than it was on the 1.6x crop-factor camera, which is what we would expect.

    Make sense?

    Cheers

  4. #4
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    Dec 2008
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    Re: Depth of Field

    Thank you All for having corrected my erroneous supposition. The DOF calculator results are making sense now.

    Regards,
    Xtack

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