What is the very tiny pin's function on the Canon FD mount?

[David Lyga]

Sorry, don't have a picture but if this is not answered, I might do just that.

There is a tiny pin on the bottom of the Canon FD lens mount. I am not talking about the larger pin, near the top point where the lens is engaged onto the camera and thus allows the breech mount ring to turn, but, instead, a tiny pin that probably measures only about 1/3 mm in diameter.

What is its purpose as, even without it, the lens functions normally? - David Lyga

 

[Mackinaw]

The very tiny pin at the 4:00 position is the AE pin. When you turn the lens aperture ring to the "A" mark, the pin pops out engaging linkage in the camera body allowing for shutter-speed preferred auto exposure (think Canon EF, AE-1, etc.).

 

[David Lyga]

Thank you, Mackinaw. It is amazing how many little things we don't know. - David Lyga

 

[AgX]

Important:
If you want to mount a FD-lens on a FL-mount (FL camera or FL bellows), always set the the aperture ring to an aperture value (thus off A) before.
Otherwise the protruding pin would hamper mounting.

With old-FD lenses the pin is retracted by that.
With new-FD lenses the pin is just unlocked, though to same effect.

The AV-1 and the AT-1, that lack the respective linkage, nevertheless yield the respective hole in the mount, thus enabling hassle-free mounting.
The earlier cameras and accessories, that use the FL mount, lack not only that linkage but that hole too.

 

[Theo Sulphate]

Even with an FD-mount camera that has no autoexposure, such as the FTb, the lens must not be on A for mounting.

Don't ask how long it took me to discover this...

 

[AgX]

Interesting. So not all FD cameras got that hole.


(Another proof that the FD mount is the most complex of all...)

 

[Theo Sulphate]

Well, to make my statement more accurate, the FTb also accepts FL lenses, so that probably accounts for why an FD lens can't be on A when mounting.

Complex - yes. With any other lens I have no problem playing with its pins and levers (for example, to ensure the aperture blades operate quickly). With an FD lens, unless it's in a ready-to-mount state, I'm terrified of touching it.

 

[AgX]

You can't do anything wrong with a FD lens. It is very robust.

The FD camera would be something different.

 

[David Lyga]

Even with an FD-mount camera that has no autoexposure, such as the FTb, the lens must not be on A for mounting.

Don't ask how long it took me to discover this...

This is one of those things whereby one knows through past, even vast, experience, but forgets anew. I can not recount the number of times I could not mount an FD lens onto an Canon mechanical body, only to discover later that the "A" setting was engaged. Only through making a fool of myself is this going to be FINALLY rectified. Thank you all. - David Lyga

 

[David Lyga]

Well, to make my statement more accurate, the FTb also accepts FL lenses, so that probably accounts for why an FD lens can't be on A when mounting.

Complex - yes. With any other lens I have no problem playing with its pins and levers (for example, to ensure the aperture blades operate quickly). With an FD lens, unless it's in a ready-to-mount state, I'm terrified of touching it.

No terror involved: simply press the larger pin (at 12 o'clock) and you will be able to cheat by manually turning the breech mount (or later mount also). Then you can play with the aperture lever all you want.

Simply put, I do not like this mount and, as AGX has stated, it is overly complex. Not only that: it accumulates dirt and makes it hard to clean out that dirt, worse than any other mount extant. EOS was a prudent move, but a more prudent move would have been not making that damn FD mount in the first place. - David Lyga

 

[AgX]

It has its benefits

First, the breech lock principle, which is applied at the new-FD mount too: it not only excludes any effect of abrasion, but, much more important, it yields a force-fit connection that will not wobble even under leverage forces. In contrast to spring-loaded mounts of other manufacturers.

Second, the splitting of different actions on different actuators, and not combining them as with other mounts, yields the chance to split control actuating action at different force levels.

Third, it yielded basically downword compatibility with two earlier Canon Mounts.


The introduction of the first "electric" mount by Pentacon showed that control can be achieved without any force. But this mount only informed the body on the preset-aperture. However the aperture control in opposite direction, a need for shutter-priority auto-exposure, then would have needed electrical actuators inside the lens. Something that Canon still achieved with simple mechanics inide the lens. Let alone aperture actuating.
In both cases, Canon and Pentacon, we are speaking of 1971 resp. even 1969.