Macro: ?50mm f1.4 w/ extension tubes

Discussion in '35mm Cameras' started by Duncan J Murray, Aug 14, 2005.

  1. Hello,

    I have a (normal) 50mm f1.4 SMC-A Pentax Lens and would like to start doing
    macro photography. I have figured out that by using all three extension
    tubes on it, I'll be able to get a reproduction ratio better than 1:1. What
    I don't understand is how this can be so much cheaper than the equivalent
    Macro lens, and if there's a large pay-off in quality for the magnification.

    TIA.

    Duncan.

    P.S. Is there a cheap way to get much better than 1:1 magnification?
     
    Duncan J Murray, Aug 14, 2005
    #1
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  2. "Duncan J Murray"
    You can try reversing the lens.....Get an adapter that allows you to mount
    the lens with the optic towards the camera, instead of the other way around.
    This allows great magnification cheaply, but the edges of the photo are
    rather distorted. It works for very small objects, however, and you can try
    different lenses, as long as they all have the same filter thread size.
    (although, you can get filter size step up/down adapters pretty cheap, too.)
     
    William Graham, Aug 14, 2005
    #2
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  3. Duncan J Murray

    Tony Polson Guest

    "Duncan J Murray"

    Yes, there is a pay-off in quality. But it might still be good
    enough. If you already have the extension tubes, try using them. If
    you are happy with the quality, that's fine. Otherwise, look for a
    macro lens. You can often find cheap macro lenses on eBay.

    At magnifications greater than 1:1, you should reverse the lens. To
    do this, you need to buy a "reversing ring". One side is threaded to
    fit your filter thread, the other has a K mount to fit the camera.
    They often come up on eBay. Make sure the filter thread is the
    correct diameter for your lens.
     
    Tony Polson, Aug 15, 2005
    #3
  4. The dedicated macro lens usually is far easier to use and it has been
    corrected for close focus and usually has a very flat field of focus. These
    are expensive to make. BTW you will not find many f 1.4 macro lenses.

    Using extension tubes or bellows can get you close and may be cheaper
    than buying a macro. It also may not be as sharp or convenient. Often
    reversing the lens can help improve results at close to 1:1 or closer.
     
    Joseph Meehan, Aug 15, 2005
    #4
  5. A 50mm 1.4 lens will not make good images when used with extension
    tubes. There are reasons macro lenses are made. Buy one.
     
    uraniumcommittee, Aug 15, 2005
    #5
  6. Duncan J Murray

    Jeremy Guest

    The 1.4 lens may not have an acceptable flat field capability. I
    remember Pentax specifically recommending against its use to copy
    slides, when they made it in the screw mount.

    If you absolutely must use a normal lens for macro work, you may find
    that the f/1.7 has less straight line distortion characteristics.

    The use of extension tubes may be acceptable for experimentation or
    casual/occasional use, but if you really decide to get into macro
    photography you will want to acquire a true macro lens. They are
    optimized for this type of work and they will produce superior images.
     
    Jeremy, Aug 15, 2005
    #6
  7. Duncan J Murray

    Tony Polson Guest


    There is absolutely no need for a flat field lens for the vast
    majority of macro work. It is only important for copy work.
     
    Tony Polson, Aug 16, 2005
    #7
  8. First off, thanks for all of the replies - they've been very helpful.
    So you're saying that not only is the f1.7 superior in terms of flat field
    capability, but also in terms of distortion?

    Duncan.
     
    Duncan J Murray, Aug 16, 2005
    #8
  9. Duncan J Murray

    Jeremy Guest

    I am merely saying that, for some macro applications that require flat
    field, like slide copying or manuscript copying, the f/1.4 may not be
    ideal. Given the choice, the f/1.7 (K-mount) or the f/1.8 (screw mount)
    might be better alternatives.

    In terms of distortion, it is well-known that the fastest lenses,
    regardless of who manufactures them, have more distortion such as
    chromatic aberration. I recall reading an article by Erwin Puts where
    he noted that chromatic aberration of the f/1.4 normal lens was higher
    than a 2.8 by a factor of nine!

    The Pentax macro lenses that I own (50mm and 100mm) have maximum
    apertures of f/4.0, not 1.4 or 1.7. I presume that by keeping the
    aperture a bit smaller, they were better able to design the lenses for
    less overall distortion, a factor that would be typically more
    significant in many macro applications. (Honeywell, Pentax's former USA
    importer, did note in its promotional materials that the macro lenses
    offered sharp coverage and minimal light falloff from edge-to-edge.)

    So, to respond to your question, yes the smaller apertures should have
    less overall distortion. Whether the degree of improvement is big
    enough to justify purchasing a specialty macro lens is up to the
    photographer. I have always associated reversing rings and close-up
    lenses as being for less-critical applications.
     
    Jeremy, Aug 16, 2005
    #9
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