Sigma lens mount and PK

Discussion in 'Digital Cameras' started by Luigi de Guzman, Feb 12, 2004.

  1. Is there any truth to the rumour that the Sigma SA mount is in fact a
    Pentax PK mount? or at least that the two are somehow inter-operable?

    I've been lurking on Pentax-discuss, and I found this thread, or
    fragment of one:

    In any event, this is pretty big. If it'll take manual-focus pentax
    lenses, I'd snap up a reasonably-priced SD-9....

    Luigi de Guzman, Feb 12, 2004
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  2. Luigi de Guzman

    John Bean Guest

    Not as simple as that. The SA is similar to PK - but not the same - and the
    register distance is different. There are no mechanical couplings on the
    SA, and the stopdown lever on a PK lens prevents it from being mounted.

    However, a purpose-made adaptor for M42 is available from allowing screw mount Pentax lenses to be used in a
    manual-everything sort of way. Works very well.
    John Bean, Feb 12, 2004
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  3. Well drat. It's such a pity that such an interesting sensor should be
    wasted in a body that supports a lens line with no lenses faster than

    Looks like I'd better keep filling up the piggybank for a *istD, or to
    jump ship to Canon.


    occasional photos (comments always welcome), rantings, ravings.
    Luigi de Guzman, Feb 12, 2004
  4. Luigi de Guzman

    Jupiter Guest

    I can also recomment the d-shell M42 adapter. A bit expensive but
    very well made and comes with an M42/L39 adapter sleeve.

    The SA mount is very similar to the PK mount, but has been stated the
    body can't accept the mechanical diaphragm actuator. A Pentax-K
    T-mount adapter WILL fit but doesn't lock. The locking groove on the
    PK mount is exactly in the same position as the sprung pin on the SA
    body and I suspect drilling through the groove to make a hole will
    enable it to lock. I've just taken the mount off the back of a faulty
    PK lens and with the d-shell adapter as a template intend to convert
    it to Sigma-SA. The 3 bayonet flanges start in the same position but
    2 are slightly longer than the Sigma version. A matter of grinding
    them down to the appropriate length. That will then go on the back of
    my Sigma 600mm mirror lens which currently has a Contax mount. Exact
    registration's not so much of a problem with them as they tend to
    focus past infinity anyway (apparently to accommodate thermal
    expansion and contraction).

    I use my SD-9 on a PK microscope adapter with no problem at all. It's
    hardly likely to spin itself off that but I wouldn't trust a lens on
    it without a proper lock.

    The procedure (per d-shell) with a manual lens mounted is to set the
    camera to aperture priority, select an aperture of f5.6 on the camera,
    set the aperture on the lens to whatever you want and the camera will
    select the appropriate shutter speed. This technique works fine,
    regardless of whether you're using a manual lens alone, tubes, macro
    bellows, lens reversed or body on a microscope adapter. Mirror lockup
    also helps in these circumstances.

    I'm not getting into the silly Canon/Sigma argument. I'm perfectly
    happy with the camera and with the d-shell adapter it's become a
    specialist macro/micro tool.
    Jupiter, Feb 15, 2004
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