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Demo: De-clicking Canon FD lens to get stepless aperture
  • I would like to share my experience de-clicking FD lenses.

    Dedicated video lenses usually feature stepless aperture to allow for smooth adjustment of exposure. Most still photography lenses, in contrast, feature stepped aperture adjustment. This article demonstrates how to "de-click" Canon FD lenses to get stepless aperture.

    Before you continue, note that

    1. De-clicking is easy. All you need to do is to unscrew the rear and take out one or two things.
    2. The process will not introduce dust into your lens---the optical assembly is sealed in one piece inside the lens.
    3. There is a "cheat" that gives you continuous aperture adjustment without the hassle of opening up the lens. All you need to do is set your lens to the smallest aperture, then turn the ring on the FD adapter. The downside of this cheat is you do not have any indication of which f-stop you are at.

    With that in mind, if you still believe de-clicking is useful---and I personally do find that being the case---here is a quick demonstration on how to do so.

    1. Take apart the lens from the rear and remove parts that cause un-smooth movement

    taken apart
    You need to remove the two parts indicated by the blue arrows if you want the aperture ring to rotate smoothly. If you can stand the un-smoothness, however, you can keep the parts on---with the parts on, step 2 alone is actually sufficient to give you stepless aperture.

    2. Remove the piston

    On lens such as the the 28mm---in which you lock by rotating the whole lens---the piston underneath the aperture ring provides the click. Remove the piston de-clicks the lens. If you have kept the two parts on in the first step, you can now re-assemble the lens.

    If instead your FD lens locks with a rotating metal ring, you will need to remove the two ball bearings inside the aperture ring.

    3. Removing the spring holding the aperture selector

    remove spring
    At this point if you re-assemble the lens without the jiggering parts, you will notice that the aperture bounces back when you try to set a small aperture. This is due to the spring mechanism used in FD lens' aperture control: the aperture ring is actually only capable of driving the aperture in one direction; reverse movement is driven by the spring holding the aperture selector. Removing the spring solves this issue.

    4. Linking the aperture ring to the aperture diaphragm

    Because the aperture ring is designed to only drive the aperture in one direction, you need to manually link the aperture ring to the diaphragm. Here I used a short polyester thread, lopping around the coupling pin on the diaphragm and held underneath the link on the aperture ring. Make sure the aperture size match up with the f-stop indicated on the aperture ring.

    If your FD lens locks with a rotating metal ring, you will be lopping around the coupling fork instead:

    link to driver

    5. Re-assemble the lens. It's done!

  • 8 Replies sorted by
  • Damn, that’s a great topic! Thanks, @ticoneva!

  • I have a 50mm f1.4 could you provide a bit more info on the location on screws and its a little dirty could you clean inside the lens this way as well?

  • Theojo: does your 50mm locks with a breech or not? If it locks with a breech, you can follow the steps here:

  • Great topic. I think he used the 28mm f2.8 I have a full nFD set, and have been looking to do this for a while. As I have 3 "spare" FDs that were not as good as the 5 in the set, I think I will test on one of them first. In any case, any extra info would be greatly appreciated.

  • awesome!

  • Wonderful topic and pics, which if everyone clicks on goes to a link where you can see the original full size pics which make it very easy to understand. I will hopefully start picking up some cheap FD lenses soon, so I am very happy to find this post. Thanks Tikoneva!!

    P.S. I think LeeM's post should be removed on the grounds of general douchery .

  • Hi! This thread is very useful and I was a complete beginner. this provided the information that I needed. I was working with a breech lock lens, which uses the rotating metal ring to lock into place, (the one in the last picture) and I wanted to point out that Polyester thread or even multiple layers fishing line would not hold. instead I recommend using a thin Galvanized wire which wont break after a few uses.

    I also wrapped the wire around the rear fork as opposed to the front fork and I found that this worked much better.

    It now works perfectly and hasn't come undone yet. Best of luck to anyone who attempts this!

  • Thanks for the topic. but Does anyone know how to assemble a silver rod (the one that attach with the aperture ring and auto aperture button) back to the aperture ring because I have accidentally pop it out.

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