digital versus film focal length

Discussion in 'Digital Discussion & Q&A' started by danir, Oct 30, 2006.

  1. danir

    danir No longer a newbie, moving up!

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    I was told that because of the smaller sensor of the DSLRs there is a factor of ~1.5 in the focal length. Is this true? Does it mean that if I use a DSLR my 70-300mm lens will become equivalent to 105-450?


     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    It's not actually the focal length that is affected...that stays the same. When you take a lens from a 35mm film camera and put it on a typical DSLR...the effective Field of View is changed. The DSLR's smaller sensor essentially 'crops' the image...making it 'feel' like a longer lens.

    So a 70-300 lens on a 1.5 crop DSLR...will 'feel' the same as a 105-450 would on a 35mm film camera.
     
  3. dsp921

    dsp921 TPF Noob!

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    Yes, it's true, basically. The focal length doesn't change, it is a physical property of the lens. What changes is the effective view angle, the geometry between the lens and the sensor. The 70-300 will have the 35mm equivalent view angle of a 105-450mm.


    Edit: I hate it when someone posts the same thing that I am typing...looks like Mike beat me to it...
     
  4. danir

    danir No longer a newbie, moving up!

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    thanks
     
  5. Soocom1

    Soocom1 TPF Noob!

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    Another point on that is when the image from a 35mm frame is enlarged, to say a 4x6, the APS sized sensor has to be enlarged 1.5 times MORE to reach the same 4x6 size.
    So the final image will look as though it was taken with a lens set at a focal length 1.5 times higher than that of the 35mm, when in reality it was set at exactly the same setting.
     

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