Digital focal length compared to standard focal length?

Discussion in 'Mirrorless Digital Cameras' started by perkins, Oct 30, 2006.

  1. I've learned that digital camera lenses arent quite equal to the standard 35mm
    lenses as far as focal point measurements and such. i.e. a 10mm-22mm digital
    lense is roughly equal to about a 16mm-35mm focal length of a standard 35mm
    camera. Im curious as to why this is. and also i was wondering if there was a
    chart or overall conversion table of some sort that might help me in lense
    selections and shooting and what not. any input would be neat :)
     
  2. The focal lens is the focal lens regardless of whether you're talking about digital or film and it is the same all the time. The field of view (FOV) is what changes because of the CCD/CMOS size compared to 35mm film frame. It is also known as "crop factor".
     
  3. It has to do with the size of the negative (or in this case the digital sensor). DSLRs have digital sensors smaller than a single 35mm frame (except for the high end Canon DSLRs which ARE the same size and hence have the same effective focal length).

    The average DSLR has a sensor about the size of the ill-fated and not lamented APS sized film format. Because of that, you can envision the sensor layout on top of the 35mm frame, with lots of visible space all around the APS sized digital sensor. The lens covers the size of the 35mm frame (going far beyond the size of the sensor) so really the APS sized sensor only captures the center part of the picture.

    Now because that's true, a 50mm lens with a 1.5X crop on say a Minolta Maxxum 5D captures only the center out of the 50mm picture. And the part of the image it captures is the same image you'd get if you put a 75mm lens on a Minolta 600si film camera and stood in the same place. So effectively, it has a higher magnification, but really it's just a crop.

    Crops go from 1.3 (Leica M8) to 1.5 and 1.6 in the average DSLR. Hope that explains it.
     
  4. sorry fot the typo I meant focal length not "lens"
     
  5. A 50mm lens is a 50mm lens no matter what camera you put it on. The only thing that varies is the size of the film or sensor which gives you different fields of view with the same focal length lens. You don't need a chart. Just multiply the focal length of a lens by the "crop factor" of the DSLR you're using to get the "equivalent" focal length.
     
  6. well thanks guys, all that info together honestly makes it crystal clear. thanks. but unfortunatly now this means i dont have a true wide angle lense :( time to start savin up again...
     
  7. While you save remember that with digital it is very easy to stitch several shots together to get the wide view ... practice that with the stitch programme which probably comes on the camera's operating CD and you might decide a WA is not worth the money as I have to date. Simply shoot the shots with around 30% overlap and either use the stitch programme or do it in editing using layers where manual control can be an advantage at times. You can stitch either panoramas or 'four square' getting much wider views than other than 'fisheye' lens.
     
  8. its not so much the panoramic style view that i like to get, its more of the perspective distortion from the foreground and background that i like to get. i dont take many shots that would look good panoramic...
     

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