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 guide demonstrates how to “de-click” Canon FD lenses to get stepless aperture.
Before you continue, note that
- De-clicking is easy. All you need to do is to unscrew the rear and take out one or two things.
- The process will not introduce dust into your lens—the optical assembly is sealed in one piece inside the lens.
- 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
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
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:
5. Re-assemble the lens. It’s done!