film & digital slr lenses revisited

Discussion in 'Photography' started by \(used to be\) Fat Sam, Oct 20, 2008.

  1. Hi, sorry about this but I have another question that's bugging me.
    I'm looking at some lenses on Ebay, Minolta fit for a sony A200.
    I know that the sony A200 has a crop factor of 1.5, so a 300mm lens for a
    film slr would effectively perform as a 450mm.
    This would be wonderfull for what I'm wanting it for, but I have a problem.
    How can I tell from the listings whether a 300mm lens is 300mm in film terms
    or 300mm in digital terms?
    Is there an easy way to distinguish?

    Sorry about this, but I'm very new to the world of DSLR's and I'm still
    trying to find my feet.
    \(used to be\) Fat Sam, Oct 20, 2008
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  2. 300mm is 300mm.
    Blinky the Shark, Oct 20, 2008
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  3. So am I overcomplicating this, and just confusing myself?
    It wouldn't be the first time I've done that to be honest.

    I was told that if I bought a DLSR lens that was labelled up as 300mm, and
    attached it to my DSLR, it would perform as a 300mm lens.
    But if I bought an older film SLR lens that was labelled up as a 300mm, and
    fitted it to a DSLR, it would effectively perform as a 450mm given that the
    DSLR sensor has a 1.5 crop factor.
    I know that 300mm is 300mm regardless of what they're being used on, but my
    understanding was that the smaller sensor makes the lens behave as if it was
    longer because its length is greater in relation to the size of the imaging

    From this, I sort of assumed that there is a physical difference in the way
    an older film SLR lens and a DSLR lens is made.
    Or is the difference just in the way they're labelled?

    So assuming there is a difference between film SLR and DSLR lenses, either
    in the way they're made or the way they're labelled, is there an easy way to
    tell if it's been designed with film or digital in mind?

    Or is all that I've just said nothing more than a load of confused nonsense
    from some deranged Irishman who really needs to spend some time reading
    \(used to be\) Fat Sam, Oct 20, 2008
  4. So is there no difference between a lens made for a film SLR and a lens made
    for a digital SLR?

    Oh I know they're the same length, but don't film and digital'm not even sure what it was I was asking now, or
    whether it makes sense anymore....

    Can I just quietly walk backwards out of the room at this point, pretent the
    conversation never happened and hope nobody noticed me making a fool of
    myself by asking dumb questions?
    \(used to be\) Fat Sam, Oct 21, 2008
  5. \(used to be\) Fat Sam

    Colin.D Guest


    All lenses are marked with their actual physical dimensions entirely
    without regard to the film/sensor size. If it says on the lens 300mm
    then it's a 300mm focal length lens.

    The confusion arises because one frequently reads zoom lens specs for a
    given camera or sensor as '35mm equivalent' purely to give some idea of
    its range, as most people will be reasonably conversant with 35mm lenses.

    But you will never see a lens marked as 'equivalent' simply because the
    manufacturer cannot know the sensor size/s it will be used with.

    Colin D.
    Colin.D, Oct 21, 2008
  6. I think so, but I've been mistaken before.

    Hey, don't I know you from alt.www.webmaster and/or alt.html?
    If the DSLR has a sensor the size of a 35mm film frame it will give you
    the recorded field of view that it would on a 35mm camera.
    And it would still *be* a 300mm lens.
    That depends on the DSLR. There are different sized sensors within that
    camera category.
    I think this is the simplest way to look at it, Sam: the lens does the
    same thing on any camera, but if the sensor is smaller then it's only
    seeing some center portion of the image -- that's what the "crop factor"
    (1.5 in your example) is about. Because the smaller sensor is only seeing
    some center portion of the image it has the framing that a 450mm lens
    would have upon a 35mm film frame or a big sensor that is the size of a
    35mm film frame.
    The difference is in how much of the image the lens "sends" to the film
    or sensor *hat sensor sees*
    Blinky the Shark, Oct 21, 2008
  7. ^^^^^^^^^^^^^^^^^

    ....*the sensor sees*.
    Blinky the Shark, Oct 21, 2008
  8. Sadly, I didn't have that excuse.
    It just sounded like I was drunk ;-)

    I think I'm starting to get it.
    Give me time. It will sink in eventually. Thanks for being patient with me.
    \(used to be\) Fat Sam, Oct 21, 2008
  9. Indeed you do.
    I've asked my fair share of dumb questions in there too ;-)
    Right, I think I'm getting this...
    So if I understand correctly, my previous understanding was slightly in

    So if I took two 300mm lenses, one from an older film slr and one that was
    designed with a dslr in mind, and fitted them both to the same dslr with a
    1.5 crop factor and took the same photo with both, neither would get me any
    closer in to the action than the other? Is that right?
    My previously (probably wrong) understanding was that the older lens would
    get me further into the action.
    \(used to be\) Fat Sam, Oct 21, 2008
  10. \(used to be\) Fat Sam

    Ofnuts Guest

    There are eBay adds where everything isd one to make you believe that
    the focal length they give is an actual one when it's only an
    "equivalent 35mm" one. So beware. A honest seller will have a close-up
    picture of the lens markings, which are always actual numbers and no
    "equivalent 35mm" ones. You can also look elsewhere for existing Minolta
    lenses and se if Minolta ever produced the 300mm-f/4 or only did a
    Ofnuts, Oct 21, 2008
  11. \(used to be\) Fat Sam

    Alex Monro Guest

    Yes, I think you've got it right now.

    The difference in so called "designed for digital" lenses is that they
    usually have a smaller image circle, which allows them to have smaller
    glass elements, which makes them smaller, lighter, and cheaper, but
    will give dark corners when used on a full frame digital or film camera.
    They often also have better coatings and baffles to reduce flare and
    ghosting, which can be a problem with digital due to the higher
    reflectivity of the sensor compared with film. They may also be more
    telecentric in design, making light rays meet the sensor at a more
    perpendicular angle, to reduce the corner fall off effect due to the
    well of the photodiodes in the sensor. This has nothing to do with
    focal length and angle of view.

    Manufacturers have different names for their digital lenses - Canon call
    theirs EF-S, Nikon DX, Pentax DA, Sigma DC, and Tamron DiII, amongst
    other terms. Some terms, such as Sigma DG and Tamron Di (no "II") refer
    to lenses which have improved coatings, but still cover a full 35mm
    Alex Monro, Oct 21, 2008
  12. Fantastic, thanks :)
    As I suspected, I was confusing myself by trying to make it more complicated
    than it actually is, LOL.
    \(used to be\) Fat Sam, Oct 21, 2008
  13. Dunno about that, but it sure gave me a laugh...Thanks.
    \(used to be\) Fat Sam, Oct 21, 2008
  14. \(used to be\) Fat Sam

    Noons Guest

    (used to be) Fat Sam wrote,on my timestamp of 21/10/2008 5:57 PM:
    never be afraid to ask questions,
    to not do so is much worse than
    not knowing
    Noons, Oct 22, 2008
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