2X or 1.4X converters on DSLRs, and the 'crop factor'

Discussion in 'Digital Photography' started by Phil Stripling, Jan 30, 2005.

  1. Another poster has asked about a 2X Quantaray converter on a zoom
    lens. Many people in the 35mm film arena suggest never using more than a
    1.4X converter because any imperfections in the lens (and the converter)
    are magnified, along with losses in contrast, saturation, and so on.

    If a DSLR already has a 'crop factor' of, say, 1.5 is the lens already
    stressed to its maximum? Does the crop factor have the same effect on lens
    quality as putting a converter on the lens for a 35mm film camera?
     
    Phil Stripling, Jan 30, 2005
    #1
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  2. Phil Stripling

    Bill Hilton Guest

    Many people in the 35mm film arena suggest never using­ more than a
    Good advice for cheap lenses, but with high quality lenses and matched
    t/c's you still get good results. We use a 2x with a 500 f/4 L IS
    often and the image quality is very high, but the lens is very
    expensive. With even a 100-400 L IS lens I'd expect poor results.
    The 'crop factor' means you are using the sweet spot of the lens,
    cropping off the edges where most problems show up, so it's the
    opposite of what you say.

    Bill
     
    Bill Hilton, Jan 30, 2005
    #2
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  3. Phil Stripling

    Skip M Guest

    Another reason to use a 1.4 rather than a 2x is that Canon's less than top
    line cameras, film and digital, won't autofocus at a max aperture of less
    than f5.6. A 2x on an f2.8 lens gets you that, a 1.4x on an f4 lens stays
    within limits, but a 2x on an f5.6 lens may have problems. With a Canon
    telelconverter, it won't AF, with an after market converter, you may have
    metering problems, since those converters tell the camera that it's really
    at f5.6, so you might end up underexposed by a stop or more. You can always
    crank in some EC, of course.
     
    Skip M, Jan 30, 2005
    #3
  4. Well, using teleconverters is never going to improve the quality.
     
    Randall Ainsworth, Jan 30, 2005
    #4
  5. Phil Stripling

    Tony Guest

    Tony, Jan 31, 2005
    #5
  6. Phil Stripling

    JPS Guest

    In message <>,
    I've taken shots with my 100-400 and a Tamron 2x that were sharp enough,
    though not spectacular. It usually involves stopping down, though.

    With a D30 the 2x might do a lot better.
    .... but you still are cutting the lens' resolution per frame height or
    width by 33% with a 1.5x crop. The corners may be worse, full-frame, if
    the quality dropoff at the corners is dramatic (more than 1.5x worse
    than the corners of the crop). People seem to forget this fact in this
    type of discussion.

    --
     
    JPS, Feb 1, 2005
    #6
  7. Phil Stripling

    JPS Guest

    In message <300120051416575885%>,
    Yes they can, Archie. If you have a lens that is sharper than the
    sensor (or film grain) can resolve, then a teleconverter will capture
    more detail. I don't expect you to be able to comprehend this.
    --
     
    JPS, Feb 1, 2005
    #7
  8. Phil Stripling

    bj286 Guest

    No, it shouldn't. After the 2x, f/5.6 becomes effectively f/11. Even
    though the converter doesn't tell the camera about this, and the camera
    still assumes f/5.6, the light passes through f/11 effective. So the
    meter sees less light. It does not need to know that it's because f/5.6
    changed to f/11, but just concludes that the light gets dimmer and sets
    the correct shutter speed and/or sensitivity.
     
    bj286, Feb 19, 2005
    #8
  9. Phil Stripling

    Skip M Guest

    Really, I wouldn't have thunk it...
     
    Skip M, Feb 20, 2005
    #9
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