Nikkor 105 2.5 AI-S Aperture Behavior

Discussion in 'Nikon' started by matthew_vortex, Dec 25, 2017.

  1. I’ve recently purchased a 105 2.5. Shot some test images in manual on my D3300, and very excited about this lens. I noticed a weird behavior though. Wondering if it’s normal.
    Focused at infinity and aperture at 2.5, everything is normal.
    If I click over to 2.8 or above, the leaves enter the aperture, but just barely.
    Say I stopped down to f5.6. As I focus closer, the lens actually stops down to approx 5.6. If I stop down to 11or 16, the aperture does not shrink. Still approx 5.6. If at 4, it does not stop down past 4.
    Lens snaps down to whatever aperture is set when I expose. Aperture lever in rear of lens is smooth and quick.
    Does it make sense that the aperture varies with focus (smaller diameter as you focus closer)?
    Thank you all.

    P.S. This is not the macro 105
    P.P.S I plan to use this lens on my N2000 and (eventually) an FE2.
  2. Vincent Peri

    Vincent Peri Metairie, LA

    If I understand you right, NO that's NOT normal.

    What exactly are you doing. Are you looking down the front of the lens as you press the stop down lever and focus closer?

    If so, there's a big problem with the lens' aperture blades. I'd send the lens back for a refund.
  3. Thanks, Vincent. I was afraid of that. And yes, both held in hand with stop down lever actuated and mounted on front of camera I observe the same phenomenon.
    Doesn’t matter with Manual mode, but I’m worried about Aperture priority because I’ll be metering through f4 while the camera thinks I’m metering at 2.5.
    Plus it’s THE Nikkor 105 2.5. It should be right.
    I have reached out to the seller to see if we can reach some resolution.
  4. m42dave

    m42dave Dave E.

    In other lens constructions I have seen, stopping down the lens moves a lever which is connected to a guide rod/bar on the diaphragm mechanism. If this rod is bent, then it could possibly change the size of the aperture as the length of the lens changes during focusing. I don't see how that could happen unless someone along the line had disassembled the lens and maybe bent a part or didn't put something back right.
    Last edited: Dec 25, 2017
  5. When you set the aperture on the lens, the diaphragm should not move until you actually take a picture. If it moves then it's more of a problem with the camera than the lens.
  6. Not necessarily. If the stop down tab on the lens has been bent so that it doesn't fully interact with the one in mirror box, it could cause this condition.

    Of course, the same thing can happen on the one in the mirror box.

    I've seen a half dozen bent lens tabs and only one bent mirror box tab.

    The key would be to see if the problem follows the lens or the body...or if you have others to which to compare it see which is amiss.
  7. If I am not mistaken, this lens won't meter with your camera, nor work in A-mode (since the camera cannot detect a lens nor an aperture setting - it lacks the mechanics for that), so even with the lens fully working (which in this case, it isn't: the aperture should remain wide open), it won't meter nor work in A-mode.

    In that sense, if it works correctly for exposures on any given aperture, and the lens is fine otherwise, you could possibly just continue to use it.
  8. ShunCheung

    ShunCheung Moderator

    The lens in question is a 105mm/f2.5 AI-S manual-focus lens, in its days a very well known lens for portrait. Unless an aftermarket CPU is added to it, the D3300 certainly cannot meter with that lens.

    If you unmount that lens from the camera body, and if you turn the aperture ring, the aperture diaphragm should open and close with the turning of the aperture ring. If you mount the lens on a Nikon SLR body, the aperture diaphragm should stay wide open for metering and composition (until you press on the depth of field preview or the shutter to capture an image).
  9. ... and, if you close the aperture with the lens unmounted, you should be able to flick the aperture open and closed with the small lens tab. If it's sluggish, it needs work. If it passes that test, it's probably OK.
  10. Thanks for all of the input guys.
    You all are correct regarding manual only on the D3300. My metering concerns relate to my N2000 and FE2.
    It feels like M42dave nailed it. There’s some play in the aperture lever, which increases with lens length (I.e., closer focus). After looking at some of my other lenses, it feels like there’s an actual rod on the diaphragm which is loose.
    Still trying to arrange a return.
  11. Just to be clear... It's normal for the reported aperture to change as you adjust focal length on a zoom lens - I believe Canon always report the aperture relative to the lens focal length (so the aperture doesn't change with focus distance), but Nikon report aperture relative to the sensor-to-exit-aperture distance. That is, the "f-stop" in the finder of a Nikon is correct for macro exposures (where the lens extends enough to affect the aperture significantly), whereas the readout on a Canon isn't.

    That said, this behaviour should be true at all apertures, Matthew did say this isn't a macro lens (a 1:1 macro could go from f/2.8 to f/5.6, but a conventional lens shouldn't), and I've no idea whether this metering system is true for an AI lens (I've only ever looked on an AF macro).

    Just bringing it up for anyone else stinking across this thread and thinking their lens is broken...

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