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Thread: The relationship between focal length, focal distance and aperture?

  1. #1

    Default The relationship between focal length, focal distance and aperture?

    If i use a 50mm f1.4 for a subject that is 5metres away, is the result the same as using a 100mm f2.8 for the subject at 10metres away?

  2. #2
    Moderator ziploc's Avatar
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    Default Re: The relationship between focal length, focal distance and aperture?

    The simple reply is no.

    With a circle of confusion of 0.03mm, the DOF with 50mm f/1.4 @ 5m is 4.61-5.46m. With 100mm f/2.8 @10m the DOF is 9.23-10.9m assuming the same circle of confusion size. You can use the DOF chart or online DOF calculator to find the DOF limits. Here is one such website:

    http://www.dofmaster.com/dofjs.html

    Cheers.

  3. #3

    Default Re: The relationship between focal length, focal distance and aperture?

    Quote Originally Posted by ziploc View Post
    The simple reply is no.

    With a circle of confusion of 0.03mm, the DOF with 50mm f/1.4 @ 5m is 4.61-5.46m. With 100mm f/2.8 @10m the DOF is 9.23-10.9m assuming the same circle of confusion size. You can use the DOF chart or online DOF calculator to find the DOF limits. Here is one such website:

    http://www.dofmaster.com/dofjs.html

    Cheers.
    can also add the difference in perspective..scene/subject/background will look different because the distance is different..the farther you are the flatter the perspective becomes

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