David Oswald wrote:
--SNIP--
Thanks for the clarification, Godfrey. You are right. I was blurring
the distinction between auto aperture, and auto diaphragm, and there
certanly is a difference.
I too have the SMC Pentax-FA 50mm f/1.4, and love the lens. My wife
calls it her lens. Not sure why, except that whenever I grab the camera
after she has used it I find the 50mm mounted on it. :) Strictly
speaking, I've had the lens at least twice as long as I've had her. lol
While on the topic of lenses, I have a love hate relationship with my
16-45. I love it because it's so good that I don't get that feeling of
"I wish I had taken that shot with a prime." I hate it because it is so
good that I can't seem to justify buying standard and wide primes within
its zoom range. It is the only thing standing between me and a 35mm
f/2, a 20mm f/2.8, or a 14mm f/2.8.
The K/M lenses are Auto Aperture/Auto Diaphragm coupled (that's actually
the same thing). However the digital bodies to not have a mechanical
aperture follower which communicates selected aperture to the body, they
also do not have linear aperture couplings. A and later lenses
communicate min/max aperture data and have linear aperture coupling, so
you can set aperture on the body in all modes. The fact that K/M lenses
don't have linear aperture coupling is the reason you can't modify a K/M
lens to A lens specs, as you can add the basic aperture communication,
which enables matrix metering as it's just contact patterns on the
mount, but there's also the A contact which indicates if a lens is set
to A. F, FA, DA and D-FA lenses have an extra contact which transmits
information between lens and camera.
I find that M42 lenses work better than K/M lenses on the DSLR's. You
get true Aperture Priority and a quick Auto/Manual Aperture switch on
some of them. I use a Super Takumar 50/1.4 on my D quite happily,
although I'd recommend getting at least an SMC Takumar 50/1.4 for the
better coating. They're way cheaper than FA's too.
-Adam
