Pentax screw mount adapter

Discussion in 'Pentax' started by Terry, Mar 2, 2006.

  1. Terry

    Terry Guest

    A friend of mine has several old screw mount Pentax lenses. He wants to get
    a digital SLR. Does Pentax make an adapter so that he could use these
    lenses with a current model?
     
    Terry, Mar 2, 2006
    #1
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  2. ^^^^^^^^^^^^

    This is the wrong newsgroup, eh?
    There are screw mount lense adapters made for many DSLR cameras.
    But... the results vary, and are not likely to be satisfactory
    except for certain uses, such as on a bellows or for posed
    portraits.

    The adapter puts the lense farther away from the plane of the
    sensor, in most cases, than the lense was designed for. That
    means the lense cannot focus on infinity without adding a
    corrective element in the adapter. As one example, typical
    simple adapters for Nikon cameras sell for $5 to $10 and with
    the a corrective element they go for $30 to $70. The added
    corrective element is guaranteed to degrade the image, though how
    much probably varies from one model to another.

    Some cameras may not have that problem, so a bit of research is
    needed to know about any particular camera mount.

    However, much worse than any of the above is that all automatic
    aperture functionality is lost. An automatic aperture screw
    mount lense becomes a manual stop down lense. (Older pre-set
    versions are actually easier to use!)

    Of course for photomacrography using a bellows or with a
    reversing ring, none of the above makes any difference at all!
    Any lense, screw mount or not, used that way becomes a totally
    manual lense. Hence a screw mount lense that is good for
    photomacrography using a bellows will serve just as well with a
    new DSLR as it did with an old camera.

    For close focusing where rapid operation is not needed, a screw
    mount lense that will not focus on infinity is still useful. I
    sometimes use a Russian made Jupiter-9 85mm f/2 pre-set screw
    mount lense just for fun (and because with 15 rounded blades in
    the diaphragm it has nice round out of focus highlights even when
    stopped down).

    Generally though, a modern auto aperture lense with Auto Focus
    is *by far* more useful than a screw mount lense.
     
    Floyd L. Davidson, Mar 2, 2006
    #2
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  3. Terry

    Tony Polson Guest


    Wrong.

    It depends on the brand of DSLR in use, but M42 screw mount lenses
    have very wide compatibility with DSLRs because the lens mount flange
    to film plane distance of the M42 mount is so large.

    Pentax manufactures a $30 adapter that allows M42 lenses to be used on
    all Pentax DSLRs in aperture priority AE and metered manual modes,
    giving excellent results. There is a selection of adapters that are
    widely available for mounting M42 mount lenses on Canon DSLRs. In all
    cases, infinity focus is maintained.

    The optical excellence of Pentax and some other brands of M42 mount
    lenses, coupled with their low prices and the ease of mounting them,
    means that screw mount lenses are surprisingly popular for use with
    Canon DSLRs.
     
    Tony Polson, Mar 2, 2006
    #3
  4. : A friend of mine has several old screw mount Pentax lenses. He wants to get
    : a digital SLR. Does Pentax make an adapter so that he could use these
    : lenses with a current model?

    Pentax makes an adapter for putting M42 screw mount lenses on Pentax K
    mount cameras. There are 3rd party adapters for mounting M42 lenses on
    both Pentax K mount cameras and other SLRs. B&H and other online stores
    will list the available adapters.

    If you have a Pentax K mount system, the genuine Pentax adapter is
    much nicer than the 3rd party adapters. Both work once mounted, but
    the Pentax adapter is much easier to put on and take off.

    Warren B. Hapke


    : --
    : Terry
    : Remove the rodent from my email address to reply directly.
     
    Warren B. Hapke, Mar 2, 2006
    #4
  5. Not wrong. Learn to read. For most, but not for all, is significant.

    Clearly there *are* camera mounts where the adapter distance is not
    a problem. And just as clearly there *are* mounts where it is a problem.
    That is true, and that is what I said.

    Your discussion is of course correct. It only applies to the specific
    mounts (Pentax and Canon) mentioned. That is why I said the results
    vary and that the OP needs to research any *specific* model.
    And automatic aperture operation is not.
    I discussed the reasons for that in detail.
     
    Floyd L. Davidson, Mar 3, 2006
    #5
  6. Terry

    Peter Irwin Guest

    It is a problem for Nikon-F mount and for Leica-R mount,
    it isn't a problem for Pentax *ist, Canon EOS, or
    Olympus 4/3. I'm not sure I understand your definition
    of "most".

    Peter.
     
    Peter Irwin, Mar 3, 2006
    #6
  7. Terry

    Matt Guest

    I use an EOS-M42 (the Pentax screw) adapter on my Canon EOS film
    camera (which has the same mount as the Canon digital SLRs).

    I really like the results, aperture priority autoexposure still works
    so you can set the aperture on the lens and the camera will set the
    shutter speed. Since I rarely, if ever, have need for shutter-priority
    autoexposure or autofocus this is a good solution and lets me use my
    small(ish) collection of mostly 1970s Japanese screwmount lenses.

    My adapter was an ebay purchase and cost me approx. $20 US.

    The only problem I've found is that some lenses project too far at the
    rear for the mirror to clear them -- in particular one Rikkenon f1.7
    50mm lens fouls the mirror when focused to infinity.

    That said, there are occasions when it would be useful to have a
    modern autofocus prime lens, but there is nothing to stop you using
    screwmounts on Canon (or Pentax) dSLRs with the correct adapter.

    Matt
     
    Matt, Mar 3, 2006
    #7
  8. Terry

    Matt Clara Guest

    Floyd must be off tonight...he never lets anyone get the last word in...
     
    Matt Clara, Mar 4, 2006
    #8
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