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Can't use aperture ring with certain PK lenses + fotodiox adapter

Discussion in 'Adapted Lenses' started by pood, Oct 12, 2012.

  1. pood

    pood Mu-43 Rookie

    Aug 27, 2012
    Using this Fotodiox PK to m43 adapter:Amazon.com: Fotodiox Lens Mount Adapter, Pentax K (PK) to Micro 4/3 Olympus PEN and Panasonic Lumix Cameras: Camera & Photo

    I have a Rokinon MC 28mm f/2.8 that has the aperture dial, but it just doesn't step down, it's always wide open, even if if I set at F22, it still shoots like f2.8

    While using the same adapter with my friend's Pentax 50mm SMC F1.4, it works.
    I can physically see the fins getting smaller on the 50mm when I turn the dial (without releasing the shutter).

  2. uci2ci

    uci2ci Mu-43 All-Pro

    Jun 22, 2012
    Los Angeles, CA
    If there are any levers in the back of the lens, try holding it with your hand and change the aperature. If that works, then there should be an arm in the adaptor that complements that lever and holds it back in place when the lens is attached. If not, then the adapter is defective.

    I dont have k mount lenses, but my canon fd lenses have to lined up a certain way with the adapter so that the aperature ring funcions
  3. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL
    I disagree that the adapter would be "defective".

    All Pentax/Asahi/Takumar lenses have an A/M switch to close the diaphram when the camera doesn't press the pin on the rear. These would not only not need the adapter to hold the pin in but also would suffer functionality loss if used with such an adapter. When the adapter doesn't press the pin these lenses function as "pre-set" lenses rather than as "manual" lenses.

    Using my Auto-Takumar 55 f/1.8 on a Fotodiox adapter is faster and easier than using my Leica Summicaron 50 f/2 on an adapter. The Takumar functions as a pre-set lens. I "pre-set" the desired shooting aperture and can switch between maximum, for focusing, and shooting apertures with a simply flick of the switch. The Leica lens is pure manual and much slower to use when not shooting wide open.

    Its true that many m42 lenses by other manufacturers that were made after the near universal adoption of TTL meters omit this lens function, relying on the body's stopdown metering action to provide the equivalent function (e.g. for DOF preview, ...). With these, you need to have an adapter that provides the stopdown function. The the adapter's method is to always hold the pin pressed then the lens will function as a manual lens. If you are buying lenses to use on an m42 adapter, I advise looking only for lenses with their own stopdown function built-in.
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