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How easy is it to repair OM bayonet mount?

Discussion in 'Adapted Lenses' started by iGonzoid, May 17, 2013.

  1. iGonzoid

    iGonzoid Mu-43 Veteran

    247
    Feb 6, 2011
    Tasmania, Australia
    Problem: Bargain lens [Sigma 135mm f2.8-64mm "Pantel" in OM mount] has one of its little levers [there are two on the outside of the lens barrel] for lens mounting non-functional — no spring action [lever just flops around in the slot] and I am loath to mount it on my OM-m43 adaptor to test out the rest of its functioning. I have a 3x Vivitar tele-extender in OM mount which I am prepared to sacrifice for parts if a repair is relatively easy for my friendly local lens mechanic/techie. I can only see him on Monday. Just wonder if anyone else has had similar problems and what the prognosis is. Thanks in anticipation.
     
  2. speedandstyle

    speedandstyle Mu-43 Hall of Famer

    On the OM mount one lever is the aperture indicator coupling and the other is the automatic iris control. The spring for the iris control has either come off or busted or is stretched. Mount the lens to the adaptor and hold it up, looking through and adjust the aperture ring. If the aperture opens and closes then you can use that lens on m4/3! The coupling and iris control are not really used, the mount does have a pin that will hold the iris control lever.
     
  3. iGonzoid

    iGonzoid Mu-43 Veteran

    247
    Feb 6, 2011
    Tasmania, Australia
    Hi, thanks to speedanstyle. Just before reading your post, I re-examined the lens and found that, you're right, one of the levers that is still spring-loaded, does close down the aperture. However, the other seems to be missing its spring mechanism. I get your explanation, but once mounted on to an adaptor, how will I unmount it if the mount/unmount lever is non-functional? Thanks in anticipation.
     
  4. fredlong

    fredlong Just this guy...

    Apr 18, 2011
    Massachusetts USA
    Fred
    Leave it on it's own dedicated adaptor.

    Fred
     
  5. Ross the fiddler

    Ross the fiddler Mu-43 Hall of Famer

    The other is (or should be) directly (or solidly) linked to the aperture selection ring & will move as the ring is moved & this is a mechanical feedback to the OM film camera for the aperture value (for metering purposes). The spring loaded lever or iris control lever (as explained above) closes down the aperture (operated from the film OM camera body) when the shutter is activated in the film camera. When using the OM to 4/3's or M4/3's adapter there is a small fixed lever (once mounted) to activate the lens aperture iris lever so when adjusting the aperture control ring (on the lens) it will physically & directly adjust the aperture iris.

    The two release buttons on the outside of the lens operate two things separately. One is to move the iris control lever to clear the aperture control lever in the OM film camera (which doesn't matter for the OM adapter) while the other one pushes in the lens locking lug. If this one is no longer spring loaded (due to spring failure), then it won't spring out to lock the lens in place in the adapter, but seeing it would be a firm fit in the adapter anyway, it might not be a big problem when using it, but your problem or description seems to be about the aperture feedback lever though which sounds like it is what it should be anyhow, unless the mount has been removed as some point & not been put back correctly, with the lever in the mount not located in the connection to the aperture ring (but this would not matter when using the adapter). If this is the case, the mount can be unscrewed (with a jewellers screw driver) & the lever correctly relocated to connect, but don't do this if you are not confident in doing it.
     
  6. dwig

    dwig Mu-43 Top Veteran

    622
    Jun 26, 2010
    Key West FL
    Mounting/unmounting is affected by the spring loaded "latch" that is controlled by one of the buttons on the outside of the lens barrel. If this is working there should be no issue with mounting and unmounting from an adapter.

    The two "internal" levers on the back of the lens are not used by OM>m43 adapters. Of these, one has spring action for opening and closing the aperture. The other has a solid connection to the f/stop ring and signals the set aperture to an OM body's metering. If this lever is loose it's an indication that the lens was probably "repaired" (poorly??) and reassembled improperly. This loose lever would be a serious fault if used on an OM body, but would be a non-issue if used on an OM>m43 adapter.
     
  7. iGonzoid

    iGonzoid Mu-43 Veteran

    247
    Feb 6, 2011
    Tasmania, Australia
    Thanks so much, guys for all your input. I am off to the radio studio for a shift reading news, but when I get back I will take some macro pix of the problem and put them up here. Definitely the aperture close-down is working. The latch [good word choice] to unlock the bayonet mount is the problem with the lever just sliding around in a slot, not attached to anything. Watch this space.
     
  8. speedandstyle

    speedandstyle Mu-43 Hall of Famer

    OK, I see what you are talking about - the buttons on the sides and not the tab levers on the mount face. One is the release and the other one is the DOF preview which activates the iris to whatever f-stop you have it set to. It sounds like your release button is busted or the spring is. It will either lock on and you won't be able to get it off or it won't lock at all. You will need to fix it to use that lens.

    There should be a tiny torsion type spring for the release. It may have just slipped off the mount and thus simply needs to be put back. More likely though the spring is busted or worse the spring mount is. Be super careful taking it apart!!! Keep it upright and do not let the aperture ring come off. If the aperture ring does come off it may be hard to get things realigned and the click-stop spring will pop out{and they are tiny!!!}{trust me, I now have a clickless lens for this very reason!}. When you go to put the mount face back on make sure everything is lined up correctly. There will be a pin that has to line up with a spring loaded lever that operates the auto-aperture.

    Good luck!
     
  9. iGonzoid

    iGonzoid Mu-43 Veteran

    247
    Feb 6, 2011
    Tasmania, Australia
    Thanks again for all your advice. Here are pix of the problem — however I have decided to return the lens and demand a refund.
    Another problem has emerged, the aperture ring won't turn all the way to the f64 "Pantel" setting — the very reason I want the lens; to experiment with extreme DoF on a longish tele. It is supposed to deliver DoF at f64 of 4.5m to ∞ when set at its hyperfocal distance [we'll see about resolution when we get there]. I have actually just bought another example off ebay, about $40 cheaper and, hopefully, fully operational.

    This is the mount latch button/lever as it should be...

    5180023MountLatch.

    This is the lever sliding around in its slot because it has no spring...

    5180024MountLatchLooseExt.

    This is the interior view, showing lack of any spring mechanism...

    5180026InsideMountLatchLoose.

    This shows the lever in position but no pin or bolt emerging from that round hole to lock the lens in position...

    5180027MountLatch.

    And finally, the aperture ring failing to make it to the Pantel [f64] position...

    5180035PantelApertureRing.

    Gimme a full refund, dude.