AgX, after rereading your posts, I'm still a bit confused because of your terminology. Can you describe in more detail this "aperture simulator"? Are you referring to the stop-down lever? It's the only thing I can think of on a camera such as the FTb that, when engaged, turns the camera into one that's metering based on the aperture selected
Canon employed basically two actuators
-) Automatic Diaphragm lever (that big lever...)
It actually drives the diaphragm in closing. It goes to completion so to say and makes it easy for the camera to actuate it. Just drive it full... The preset setting at the lens will take control and in effect disengage it once the preset aperture value has been reached in closing.
-) Aperture Simulator / Aperture Control lever (that small lever...)
When using the lens in
open-aperture mode with preset-aperture, this lever will tell the camera body on what aperture settting the metering or the auto-exposure has to be based on. That is why it is called aperture simulator.
This feature is substantial in any kind of open-aperture metering. The Practica Electric mount instead of a lever offered the camera a varying electrical resistance to indicate the aperture preset at the lens.
When in
shutter-priority autoexposure-mode the
same lever changes its role from being active to being passive. Now it is the camera body that swings this lever to a degree that at the respective, pre-calculated diaphragm opening the action of the automatic-diasphragm lever will be disengaged. That is why I call it also aperture control lever.
In addition there are
-) Lens Speed indicator
Informing the camera body on what aperture any reading at open aperture is to be based on.
(Is it the scene that is dark, or is it the low speed of a lens that makes a scene look dark...)
-) Auto-mode indicator
Informing the camera body whether one wants to work in manual- or auto-mode.