Originally posted by LesDMess John and Dave,
The ESII manual states this precisely. Keep in mind this is the only way aperture priority auto exposure can work with auto M42 lenses.
I think there is some confusion over how M42 lenses equipped for full aperture metering work on the ESII versus non-full aperture lenses.
Metering with SMC lenses- the ones with the linkage for full aperture metering- occurs at full aperture on the ESII. The linkage tells the meter what aperture is set, rather than the diaphragm being physically stopped down for metering. The shutter speed is actually set prior to the diaphragm stopping down during the exposure sequence.. Half depressing the shutter release turns on the meter but does not stop down the lens.
Lenses without that linkage must be stopped down for proper metering on the ESII. You can use the lever on the side of the mirror box, just like the Spotmatic. Or you can set the diaphragm to manual mode. Super Takumar lenses, for example, will meter properly on the ESII (and the Spotmatic F) only when stopped down. THe sequence is that the lens is stopped down one way or another, shutter speed is captured as the shutter release is depressed, then the shutter fires. Again, there is no half-depression/stop-down function.
The Chinon CEII is a can of worms of a different colour. Half depressing the shutter release both stops down the lens and turns on the meter. Pressing the shutter release the rest of the way captures the shutter speed setting, then fires the shutter. Metering is not truly full aperture, but the half-depression/stopdown/shutter speed setting sequence means that most auto diaphragm M42 lens can be used conveniently in aperture priority mode. You are able to focus at full aperture, then quickly and briefly transition to stopped down mode as you press the shutter release and take the picture.
Hope that begins to sort things out.
John