Lens won't stop down

Discussion in 'Nikon' started by www.philwinterphotography.com, Jun 3, 2016.

  1. Hello, I have a plain prism Nikon F from the early 60's with the 50mm f1.4 lens. For some reason, the lens will not stop down when pressing the shutter. It just stays at f1.4. Everything else is fine. Does anyone have an idea of what I should look for? Is this problem likely the lens or the body?
     
  2. Sandy Vongries

    Sandy Vongries Administrator Staff Member

    So you are saying that you have set the F stop (other than 1.4 in the lens) and when you press the shutter button, the lens diaphragm doesn't stop down? I would first remove the lens and be sure the lever in the rear of the lens mount works smoothly. Second, press the preview button to the right of the lens mount and make sure the activating lever works. That's about all there is.
     
  3. The aperture on the lens is stopped down by the lever on the left side of the mirror box as you look into the camera. If you wind the camera and release the shutter, you should see the camera lever move very rapidly, if the camera connection is working.
    The corresponding lever on the back of the lens is as shown below. You should be able to move that with your finger and look into the back of the lens as the aperture blades close and open.
    Of course, none of the above will do any good if the lens is not set to something other than f/1.4; but I'm guessing you have figured this out.
    00dys6-563475584.jpg
     
  4. Just adding to the above, if not known:
    When a Nikon lens is off the camera, moving the aperture ring should visibly open and close the aperture, and you should also see the aperture lever moving. When the lens is set to 1.4, the lever will be fully counterclockwise (using JDM's image above for orientation). When it's set at F16, the lever should be clockwise, and it should be easily pushed counterclockwise to open the aperture.
    One of the things I've seen on the occasional F is a damaged aperture actuator in the camera. The lens has a tiny screw to prevent overrotation, and if that falls out, the lens can be over-rotated, and the the lever in the camera bent. Here is an old Nikon F with the actuator in its correct position and not bent. It's in the lens opening at the 9 o'clock position. When you operate the shutter, you should see that lever go down and back up.
    edit to add: if that lever is bent, and if you are adventurous, you may be able to unbend it. On an F this lever is made of brass, and can be unbent if you're careful.
    00dyss-563479184.jpg
     
  5. It if fairly common for older lenses to have grease or oil in the diaphragm blades, which will keep them open. It's not expensive to have them cleaned and the lens relubricated at a Nikon service center. I would suspect this if the lever moves freely but the lens stays open. (The lever forces the blades open, but they should return under spring tension when the lever is released.)
     
  6. Thanks to everyone who contributed, but Edward, I think you hit on it. If I take the lens off, and set the aperture to something like f5.6, I can rotate the aperture ring between f5.6 and f16, and the blades open and close like they should. Same thing happens if I start at F4. From what you have said, this is normal. But, if I start at f2.8, and close down, the blades become sluggish from f2.8 to f4. If I start at f2 or f1.4, turning the aperture ring toward f16 does not close the blades at all. It appears that the blades are sticking wide open.
    Is cleaning the blades something a reasonably mechanically savvy person could under take, or is it best left to a professional? Some time back, I actually got some nice indoor images shooting everything at f1.4. Thanks!
     
  7. I would recommend leaving it to a professional, unless "mechanically savvy" means someone trained in lens repair.
    BTW, I had the same issue with a 50mm f1.4 AIS, and after service it was like new.
     
  8. ShunCheung

    ShunCheung Administrator

    That kind of problem has happened to two of my Nikkor lenses, in 1997 and 1999 respectively. Each time Nikon charged me about $200 to replace the aperture mechanism. I have been using Nikon since 1977 and didn't have this issue before those two occasions and also haven't had them again.
    However, I wouldn't spend $200 (not yet taking inflation into account) to fix a lens from the 1960's.
     
  9. I certainly would not spend that kind of money on that lens, which is pretty common and generally not terribly expensive.
    There are facilities that might do the job of cleaning it more cheaply, but I'd check out places like KEH.com to see if a good warrantied one comes in cheaper.
    While waiting and looking around, I'd be inclined to take the lens off, and exercise it a lot, to see if it limbers up. There certainly is nothing to lose, and if the aperture is not actually greasy, but just stiff, perhaps it will free up if you keep at it. See what happens if you set it to F16, and manually move the aperture lever back and forth fifty times or so.
     
  10. To be certain the lens is not stepping down:
    1) Set the lens at f/11
    2) Look through the viewfinder and press and hold the Depth-of-Field preview button.
    If the viewfinder darkens, your lens is stepping down. If the viewfinder does not darken, your lens is not stepping down.
     
  11. Phil, there are a few things to take into account when working on lens. Screws are often secured with a clear threadlocker similar to nail polish. Acetone or nail polish remover will dissolve the threadlocker. Apply the acetone to the screw head and let it sit for 5 to 10 minutes. Use screwdrivers that fit the screw head well.
    Special spanner wrenches may be needed to remove lens elements. Some lens elements, especially the outermost ones, may have shims under them. The shims are usually brass rings .0005 inch thick to .001 inch thick. Always keep the shims with the element they came off with. Make certain to get them aligned correctly when reassembling.
    Take pictures as you disassemble the lens. Pay close attention to the lens elements as you remove them. The most common mistake is to reverse an element.
    I would start by removing the mount ring and checking the aperture operation with the mount ring off. Check the mount ring for dings. Check the aperture operating lever for bends. Isopropyl Alcohol can be used to clean the aperture blades. The blades will bend easily so be careful not to apply too much pressure to them. I use 90% Isopropyl Alcohol on a cotton swab. Be sure to remove any cotton fibers left behind.

    Extra fine powdered graphite can be used to lubricate the aperture blades pivots and mechanism. DuPont dry film teflon http://www.amazon.com/DuPont-Non-Stick-Dry-Film-Lubricant-Squeeze/dp/B011TVGYGM/ref=sr_1_5?ie=UTF8&qid=1465105497&sr=8-5&keywords=dry+film+teflon can also be used but it will cause initial stick but breaks free easily once thoroughly dry.
     
  12. Before mucking around with an ill-advised self-repair, call a Nikon facility, or "Authorized Camera Repair" in Morton Grove, IL, and get an estimate. If all the lens needs is a CLA, it will cost about $100. I've had it done on two lenses with similar symptoms, and neither required a replacement diaphragm.
    Even if the cost approaches that of an used lens, it's likely that a lens of the same vintage will require service in the near future.
     
  13. Sandy Vongries

    Sandy Vongries Administrator Staff Member

    Another 50 F1.4 AI, $40-50 on line just now.
     
  14. I have written repair instructions for large format cameras where none existed and many have used that information to successfully service their cameras. A 50mm f1.4 lens is not that complicated. Anyone with good mechanical skills and a little direction can service one. I would not recommend trying to replace the aperture assembly but removing the mount ring and rear element, straightening a bent operating lever, or cleaning a little corrosion is doable.
    I had my 35-135 f3.5-4.5 Nikkor zoom develop some fungus on a center element. Lots of fun tearing that one down to remove and clean the effected element without any instructions. I purchased a second one in pristine condition from KEH a few years later. You cannot tell the difference between the two with any image made on film or a D300.
    You each know your abilities and budget, proceed accordingly.
     
  15. Thanks for everyone's help. After reading your responses, I decided I'm not mechanically savvy enough, nor is it worth my time and frustration. I have located a factory-trained Nikon repair facility nearby, so I will check with them about the repair.
     

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