Noob question

Printable View

  • 02-22-2004, 10:07 AM
    photo101
    Noob question
    Can someone explain for me why a lens on a dslr has a different mm rating then with a film slr? What differnece does it matter what the body is, should not the mm rating be the same on the lens?

    AI have the n80 with lenses. If the ratings are differnet for digital, can I use my current lenses on a dslr when/if I purchase one?

    Confused....
  • 02-22-2004, 12:49 PM
    Michael Fanelli
    Focal Lengths
    Quote:
    Originally Posted by photo101
    Can someone explain for me why a lens on a dslr has a different mm rating then with a film slr? What differnece does it matter what the body is, should not the mm rating be the same on the lens?

    AI have the n80 with lenses. If the ratings are differnet for digital, can I use my current lenses on a dslr when/if I purchase one?

    Confused....
    The focal length of the lens does not change. That is an inherent chracteristic of the optics.

    What you are seeing are the "35mm equivalent" values. When you put a 50mm lens on a 35mm camera, an APS-sized digital sensor, a medium format camera, etc. the focal length is exactly the same but the field of view changes. As most photographers are used to thinking in terms of 35mm cameras, advertisers try to give you a rough idea of what you will see when using something that is not 35mm.

    For example, a 45mm lens on a 6x7 camera is wide angle, on a 35mm camera it is a normal, on an APS DSLR it is a mild telephoto.

    Clear as mud?
  • 02-22-2004, 03:52 PM
    photo101
    Ok
    Quote:
    Originally Posted by Michael Fanelli

    Clear as mud?
    Yes, it is clear as mud now. hehe
    So my 300mm lens would be a super zoom for digital?
  • 02-22-2004, 04:35 PM
    another view
    Yes - a 300 will be a 450 on many cameras (based on 1.5 crop factor). Another advantage here - if you used a 1.5 teleconverter to get this you'd lose a stop. Because you're not actually changing focal lengths, you don't lose a stop. Down side is on the wide angle lenses, 20mm just isn't very wide on my DSLR (Fuji S2 with 1.5 crop factor).

    You'll hear alot of names and terms to describe this: crop factor, magnification, 35mm equivalent - but "crop" comes closest to describing what happens. My 20mm lens still has the perspective of a 20mm lens but the angle of view is smaller.
  • 02-22-2004, 05:54 PM
    ustein
    >So my 300mm lens would be a super zoom for digital?

    Yes, if it is of good quality! Digital cameras show the differences of good and bad lenses.

    Uwe
  • 02-23-2004, 12:26 AM
    photo101
    Thanks for the info. Now if I just could find the cash to buy one. :)