Boris answered your first questions just right. And this Chinon (sometimes badged as Sears) is a nifty and well-thought-of lens. I have the f/2 version and would indeed like an f/1.7 copy, you betcha!
Originally posted by John71 If the camara is controling the aperture, what is the function of the aperture ring?
The camera does NOT control the aperture, except minimally. A-type lenses have the aperture lever, and electrical contacts on the lens base. Those contacts allow the camera to control the aperture. K- and M-type lenses like this Chinon have only the lever. YOU control the aperture. See below.
Quote: Curious to learn more about the combination of the aperture ring, aperture lever and controls from the camara...
If the camera is in any Auto mode, it defaults to Av, and the aperture stays wide-open when you shoot. Put the camera in M mode and hit the Green button; this stops-down the lens to your selected aperture for metering and exposures. So the camera controls the aperture ONLY to stop it down. The rest is up to you.
With K- and M- type lenses on my K20D, I'll typically leave the Mode dial at TAv, right next to M, and the lens aperture set to something comfortable. In TAv the camera defaults to Av and I shoot with the lens wide-open. This is pretty sweet with my K50/1.2! If I need a tighter aperture, a quick-flick of the dial puts me in M mode. I hit the Green button to meter, then hit the shutter to expose. That way I don't have to fiddle with the aperture ring when time may be critical.
Those are the basics. Have fun!