Full continuously variable Apeture priority with M lenses

Well, I tried testing the DOF preview in Av and M. It seems when the shutter fires, the apature closes down in any mode. But you are right, in Av the DOF preview doesn't stop down the lens whereas in M it does! I still can't figure out how I've been getting my correct exposures, since if the lens doesn't stop down with DOF preview in Apeture priority, how can I be getting correct exposures at differrent apetures with the correswponding differnt shutter speeds???

Nearest I can figure, maybe the camera is making an instantanious measurement as you make the exposure? Otherwise, I can't explain why if I shoot at a small apeture in Av I get a longer shutter speed than wide open, but the image is still properly exposed!

A mystery has been comitted. But you are correct, the lens does not shut down with DOF preview in Av but the diaphram does shut down when the shutter fires. This is all very mysterious!

I heard once that the LX measured exposure during the time the shutter was actually closed. Could this technology somehow be linked to the sensor itself? I think further research is defenitely in order here.

But you are correct that the DOF preview doesn't close the diaphram in Av, but firing he shutter does. Now I'm really puzzled!!

Dave is quite right that pulling on the DOF lever does not stop the lens down in Av mode, unless the lens is an A lens set to A. This discussion is, of course, about non-A lenses.

Furthermore, the camera has no way to "remember the aperture" of a pre-A lens, so it is a fallacy to think that it can make use of such information, even if the DOF lever were capable of imparting it, which it's not.

Arthur, I have tried pulling the DOF lever, and it makes no difference. Because you keep changing the light, you have no idea what is happening to the aperture. Mount the camera on a tripod, ensure you have a constant light source, then experiment away.

G