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OM 50mm F1.4 - How to set correct aperture

Discussion in 'Adapted Lenses' started by dayou14, Aug 25, 2011.

  1. dayou14

    dayou14 Mu-43 Regular

    59
    Jul 6, 2011
    Dear friends,

    I need a little advice here.

    OM.

    This OM lens I've gotten for some time but never really grew into it. I mate it with my GH2, and the problem is it defaults to the widest aperture (in this case F1.4), unless you press that little silver button on the left side. When you do that, the blades close down to the aperture you had set.

    I tried pressing the button down while shooting, but found it impractical. Do all OM lenses have this quirk? How do the members in this forum deal with it? Did I just got a bad copy?

    I'm looking for a solution that I can use permanently. It is so vexing I'm considering letting the lens go.

    Any advice would be appreciated. Thanks!

    Bian
     
  2. Pen F

    Pen F Mu-43 Regular

    53
    Jul 21, 2011
    Im not an expert, and sure someone more in the know will chime in. With that being said I use om lens with my ep3, and the adaptor I use stops down the lens for me after I set the apatchure ring. I am at work now so cant tell you the brand name but will look into it this evening.
     
    • Like Like x 1
  3. The problem is not the lens unless the stop-down lever on the base of the lens has gone awol, broken, etc. Your adapter may also be missing the tab that holds the lever in place.
     
    • Like Like x 1
  4. nsd20463

    nsd20463 Mu-43 Regular

    116
    Apr 30, 2011
    Santa Cruz, CA
    that's not how it is supposed to work

    That's now how it should work. When mounted on the adapter, the lens should keep its aperture blades closed down to whatever setting is selected by the aperture ring at all times.

    It works like this: the OM lens should have two tabs sticking out the back. One moves when you rotate the aperture ring in the front of the lens. It was used to indicate to an OM body what the lens' aperture setting was, and serves no purpose at all on m4/3, and you can ignore it.

    The other tab pushes against a spring and pushing on it closes the aperture. Try it and see. It was used by OM bodies to close the aperture before the shutter was released. On m4/3 the adapter plays the role of the body, and holds that tab in the closed-aperture position using (in the case of my adapter) a little screw-mounted tab inside the adapter which catches the lens's tab, and as the lens is rotated to mount it onto the adapter, pushes the lens' tab into the closed-aperture position.

    This makes a whole lot more sense when viewed in person rather than read here. Take the lens and adapter off the camera, and remove and reinstall the lens on the adapter while looking into the camera side of the adapter to see how it all fits together.

    So one easy possibility is that your adapter's tab and the lens' tab aren't catching each other b/c one or the other is bent (or missing).

    Or maybe you've forced things and put the lens onto the adapter in a wrong position. I think the OM lens mount doesn't allow this easily, but with enough force... well it's just thin metal.

    It's possible your tabs are fine, but the mechanical linkage inside the lens which releases the aperture is broken, in which case if you manually move the tab the aperture won't close. But since pushing the DoF preview button on the lens works, and since that button uses most of the same linkage to do its work, I don't think this is your source of trouble.
     
    • Like Like x 1
  5. nsd20463

    nsd20463 Mu-43 Regular

    116
    Apr 30, 2011
    Santa Cruz, CA
    from your photo

    One more idea, very very simple, and which I just realized looking at the photo you've posted: you don't have the lens fully locked on the adapter.

    The red dot on the adapter and the red dot+line on the lens should both be in the same position, and both should be on top when the lens is attached to the camera.

    So if the lens you show in the photo isn't halfway released, then that's the trouble.
     
    • Like Like x 2
  6. mauve

    mauve Mu-43 Top Veteran

    892
    Mar 9, 2010
    Paris, France
    Hawk eye. I'll bet on it too, many of those adapters are too stiff. The OP can bend the mount springs of the adapter (OM side) with pliers to loosen them somewhat. There was a discussion about that very problem a while ago.

    Cheers,
     
    • Like Like x 1
  7. thearne3

    thearne3 Mu-43 Top Veteran

    807
    Jan 28, 2010
    Redding, CT USA
    It also depends on the adapter you are using. My adapter (which cost about $14) has no 'tab'. I use a small piece of plastic to hold the 'spring tab' open. PM me for more detailed instructions.

    Best,
    Tom
     
    • Like Like x 1
  8. thearne3

    thearne3 Mu-43 Top Veteran

    807
    Jan 28, 2010
    Redding, CT USA
    Here is my adapter (which looks like yours) and the spring tab 'block' using a piece of plastic from a MetroCard:

    [​IMG]

    20110825-18-10-39_8259887OM%25252050%252520adapter.

    I had the same problem with my Pen F...same solution.
     
    • Like Like x 1
  9. The other reason for an OM adapter that does not allow the lens to rotate into the correct position is that the leading edge of the seat for the lens locking pin does not have an angle on it. On my OM-EF adapter I have depress the lens release to be able to rotate the lens far enough to seat the locking pin correctly.
     
  10. dayou14

    dayou14 Mu-43 Regular

    59
    Jul 6, 2011
    Guys,

    Thanks so much for all the responses. I would have gone for Tom's metrocard solution (thanks for taking the time to shoot it), but nsd20463 and mauve's hawk-eye actually solved it! the adapter was stiff and it's not fully locked-in. Once locked-in, it closed down the blades.

    Thanks guys once again!

    Bian
     
  11. phrenic

    phrenic Mu-43 All-Pro

    Sep 13, 2010
    Glad it was resolved! I need to order an OM adapter and I have to say this makes me a bit nervous. Seems more..fiddly than the FD adapter that I already own. What can I say, I'm from the digital era and have little understanding about the actual lens mechanics!
     
  12. The OM adapter is (or should be) one of the simplest bayonet adapters as all of the mechanics of the lens release are in the lens itself. All the adapter needs is a tab for the stop-down lever and an indent for the locking pin. Sounds simple enough...
     
  13. thearne3

    thearne3 Mu-43 Top Veteran

    807
    Jan 28, 2010
    Redding, CT USA
    True, although the Hexanons take the 1st prize in simplicity, since the aperture spring causes it to naturally be in the 'closed' position. Hence no need for a 'tab' for stop-down. I think that's why I didn't miss the tab when I got my OM adapter!

    Reviewing the pictures of OM adapters on eBay, some clearly show the tab, but for some reason none mention it as a feature. I've ordered one from China - the Fotocola - that shows the tab.
     
  14. dayou14

    dayou14 Mu-43 Regular

    59
    Jul 6, 2011
    Phrenic,

    I can say that adapters come in a wide range of price points and quality, and the one I got I got it in China and costs about $30 thereabouts. It probably isn't the highest quality and that's why it is stiff and I have to deliberately turn it all the way to the end. But once it's locked, the pin stays there and the aperture step down works.

    Bian
     
  15. nsd20463

    nsd20463 Mu-43 Regular

    116
    Apr 30, 2011
    Santa Cruz, CA
    cheap adapters and infinity focus

    I've many cheap (<$25) adapters: OM, Pen F, Nikon F, Canon FD, and a M39 screw mount. All of them except the M39 have a little tab to close down the shutter. [M39 comes from rangefinders, and thus doesn't need it]

    And like the OP, my OM and PenF adapters were a little stiff when I first got them and needed a little metal finishing to work better (I wouldnt' say "well", just "better").

    What bothers me more than stiffness in the mount is the location of the infinity focus. These adapters are manufactured just a little bit too thin, so that with poor quality manufacturing control the product can still focus to infinity. Which is fine, but when you focus at infinity the lens' focus scale reads somewhere before the stop (all the way at 3ft in the case of my OM), and not when the lens' barrel is at infinity. The end result is you can't zone focus using the markings on the lens, as they were intended to be used.

    Apparently on the OM 50 f/1.8 the four screws under the rubber focus ring can be backed out a turn, and the focus ring rotated to the desired position, and then the screws tightened back down. I haven't done it yet (I can't find my small screwdrivers, but haven't given up and bought a new set), and I have no idea from the lens diagram whether this will move the infinity stop as well.
     
    • Like Like x 1
  16. mauve

    mauve Mu-43 Top Veteran

    892
    Mar 9, 2010
    Paris, France
    Don't do that unless you intend to use the lens solely with that one adapter (and refrain from reselling it, that would be a nasty surprise for a new owner). The "proper" solution is to shim the adapter itself. You unscrew the mount OM side, and put one or two washers (cardboard, aluminum foil) between the adapter tube and the OM mount until you've reached the desired height.

    Cheers,
     
    • Like Like x 1
  17. nsd20463

    nsd20463 Mu-43 Regular

    116
    Apr 30, 2011
    Santa Cruz, CA
    Shim first

    Good point. I guess I think "muck with the lens" before "muck with the adapter" b/c in the case of the OM 50/1.8 the adapter cost me more than the not-in-the-greatest-condition lens did. :smile: But an adapter which works properly with all the lenses is more useful in the end. So I'll try shimming it and see what I get.
     
    • Like Like x 1
  18. FastCorner

    FastCorner Mu-43 Veteran

    308
    May 28, 2011
    I, too, have the 50mm f1.4. As others have mentioned, the aperture stop-down is a function of the adapter. I've bought 2 different designs that had a pin to stop down the iris, and 1 that didn't. I wouldn't say that having to press the DOF preview button the lens is a bad thing, however: sometimes you want to know exactly where the focus "center" is and focusing while stopped down makes this ambiguous.