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Adjustable extension tubes?

Discussion in 'Accessories' started by DoofClenas, Feb 12, 2014.

  1. DoofClenas

    DoofClenas Who needs a Mirror!

    943
    Nov 9, 2012
    Traverse City, MI
    Clint
    Do they make a fully adjustable extension tube for m4/3? I just bought a Jupiter 9 lens from here, and with the current setup of going from the Zenit 39 with a M42 ring adaptor to the M42 to m4/3 adaptor, I loose infinity focusing (which isn't the purpose of the lens, but it would be nice to have). I bought a m39 to M4/3 adaptor, and the thing is much shorter than the m42 to m4/3, so it but puts the lens too close to the sensor. If I had something adjustable, I could probably get spot on with it..that and then it would allow me to keep my m42 adaptor on my pentax lens.

    I'm not sure how to calculate the exact distance needed, which is why I thought fully adjustable would be better.
     
  2. Petrochemist

    Petrochemist Mu-43 Top Veteran

    652
    Mar 21, 2013
    N Essex, UK
    Mike
    Focusing helicoids are readily available in m42 and some larger sizes. Knowing the right term for an e-bay search helps considerably.
    There is even one that has a ยต4/3 mount on the body side. My copy of these is sadly just too long at it's shortest for infinity focus. It could have made a great macro capable adapter
     
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  3. dwig

    dwig Mu-43 Top Veteran

    623
    Jun 26, 2010
    Key West FL
    This should not be happening. With a properly assembled and adjusted Zenit M39 lens, a properly made M39>M42 adapter ring, and a properly made M42>m43 adapter there should be no loss of infinity focus. The Zenit M39 mount and the M42 Pentax/Praktica mount share the same 45.46mm register. Either your M39>M42 adapter isn't letting the Jupiter 9 thread all the way flush with the face of the M42>m43 adapter or the lens has been mis-assembled. I rule out the possibility that the M42>m43 adapter is out of spec since you appear to have used it with another M42 mount lens without issues.

    This would be an LTM adapter which is for Leica thread mount lenses which have a 28.8mm register distance. In theory, you would need a 16.66mm LTM extension tube to mount your Jupiter 9 via this adapter. If you could track down a 15mm tube, there were such tubes made by the Leitz office in the US known as E. Leitz New York or ELNY, the Jupiter 9 should mount fine and possibly focus a tad past infinity.

    There is a slight difference between LTM and the Zenit M39 thread which might cause issues. While the two mounts are the same 39mm diameter, the LTM mount uses an inch-standard thread at 26tpi and the Zenit mount uses a metric tread of 1tpmm, equal to 25.4tpi. The two thread types also have slightly differnent profiles that sometimes lead to binding. A properly made Zenit M39>M42 adapter will use the 1tpmm pitch and have no flange, allowing the adapted lens to mount flush with the face of the M42 body mount. A 39mm>M42 adapter that has a flange is likely intended to be a LTM>M42 adapter; something that can only be used for closeup and macro work with the intended lenses and should use the 26tpi thread.
     
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  4. DoofClenas

    DoofClenas Who needs a Mirror!

    943
    Nov 9, 2012
    Traverse City, MI
    Clint
    I'm wondering if it is was mis-assembled.
     
  5. dwig

    dwig Mu-43 Top Veteran

    623
    Jun 26, 2010
    Key West FL
    It should be easy to tell. Assemble the Jupiter 9, M39>M42 adapter, and M42>m43 adapter set and look very closely at the side of the seam between the lens and the m43 adapter. The rear face of the lens' flange should seat against the from face of the flange on the M42>m43 adapter. If there is a gap then your M39>M42 adapter is the problem, or at least part of it. If the lens sits flush to the M42>m43 adapter then the lens itself is the problem.

    Another test would be to skip the M39>M42 adapter and just hold the lens against the M42>m43 adapter while the latter is mounted on a body. With the lens set to infinity you should get infinity focus or slightly past infinity. If this fails to reach infinity focus with the Jupiter 9 but your other M42 lens does focus to infinity then there is no doubt that the Jupiter lens is at fault.
     
  6. Petrochemist

    Petrochemist Mu-43 Top Veteran

    652
    Mar 21, 2013
    N Essex, UK
    Mike
    One thing that may have a bearing...
    There are a couple of different registration distances that m39 lens were made to.
    Mine all match m42 (45.46mm), but there was also a Leica M39 with much reduced registration (under 30mm).
     
  7. DoofClenas

    DoofClenas Who needs a Mirror!

    943
    Nov 9, 2012
    Traverse City, MI
    Clint