Canon FL Automatic Diaphragm Question

[bwesso]

Hey all,

Recently picked up a FL 35mm f2.5 and have a question about how the automatic diaphragm works in these FL lenses. This model does not have the A/M switch for opting between using it or not-- it seems like it is always engaged, and the only way to stop down manually is by setting desired aperture and then engaging the aperture preview ring.

This wouldn't be an issue, but when I adjust the aperture, the preview ring moves with it when opening up, eventually resetting it to wide open. Is the aperture preview supposed to move with the aperture ring like this? I'm curious if this is just how the lens works, or if some cleaning between the two rings may remedy this behavior.

I mostly intend on using this lens mounted to a mirrorless camera, and typically like to be able to just stop down as needed without needing to keep twisting at the preview ring.

Im not too familiar with FL lenses, so if this is just standard practice, then let me know. I have the 28mm 3.5, but that one has the A/M switch.

Thanks!

 

[bwesso]

Found a post on dpreview that suggests that this is how the lens is intended to work. Oh well. Maybe now its time to ask the question as to how I can disable it haha. I'm sure its just one disconnected spring away...

 

[benjiboy]

Found a post on dpreview that suggests that this is how the lens is intended to work. Oh well. Maybe now its time to ask the question as to how I can disable it haha. I'm sure its just one disconnected spring away...

The F L range of Canon lenses had pre set diaphragms, you need the later FD lenses if you want them to have an automatic diaphragm.

 

[MarkS]

That's not quite right. The FL series lenses had automatic diaphragms, but utilized "stop-down" metering. The FD series lenses, which succeeded the FLs in the early 1970s, had more connections between the lens and camera body to allow open-aperture metering. The FD series came in with the (original) Canon F-1 and the FTb cameras. The FLs used the breech-lock mount, as did the early FD lenses; Canon changed those to a bayonet mount sometime before they introduced the AE-1.

My first good camera, in 1973, was a used (and already obsolete) Canon TL-QL. It came with an FL 50/1.4 lens, that had the A-M ring on the lens. Later I had the 35/2.5 FL lens, but I don't recall if it had the A-M ring on it. I don't recall a second (preview) f/stop ring. But that lens has been gone for a long time... and there may have been variations over its production life.
Is it possible that your 35/2.5 is an older lens, made for the Canonflex cameras of the early 1960s? I've only ever seen one of those, and was told that their lenses were not compatible with the later cameras.

Maybe you can share a picture of your lens- that may help figuring it out.

 

[dynachrome]

There is a second ring behind the aperture ring. Although it is not marked as such, it is the A/M switch. It turns a short distance from left to right. Later FL lenses like the redesigned 50/1.4 have a pin at the back with an A/M marking. The 35/2.5 FL is a decent performer, especially if stopped down a little.