[K57XR]

I’ve come across a number of old third party primes (on EBay) with the word “Auto” stamped on it. I‘ve seen it on both K and Screw mount lenses. Looking at their mount photos, I don’t see any electrical contacts of any kind, not “A” setting or even a Ricoh pin which indicates it’s a manual focus/aperture lens. What exactly is “auto” about these lenses?

[Super A-wesome]

When you look through an SLR viewfinder, you are viewing through the lens wide open, regardless of aperture setting, but when you take the shot, the aperture stops down to the selected setting. there was a time when you would have to do this yourself.
The lenses are "auto" because the aperture closes when you take the shot, and then opens back up automatically; it is not the same as an A setting. This is on every modern SLR lens, so it is no longer designated, but in the 60s and into the 70s when it was not as universal, it was designated.
I hope i'm making sense; this is quite hard to explain.

[Mike Cash]

The Auto-Takumars would shut down automatically, but you still had to cock them back open with a lever on the lens body. I believe there was an exception to this during a model transition.

[jjdgti]

Thanks for the explanation. I always wondered that but never got around to ask.

[K57XR]

When you look through an SLR viewfinder, you are viewing through the lens wide open, regardless of aperture setting, but when you take the shot, the aperture stops down to the selected setting. there was a time when you would have to do this yourself.
The lenses are "auto" because the aperture closes when you take the shot, and then opens back up automatically; it is not the same as an A setting. This is on every modern SLR lens, so it is no longer designated, but in the 60s and into the 70s when it was not as universal, it was designated.
I hope I'm making sense; this is quite hard to explain.

Your explanation makes perfect sense! I was under the impression all lenses behaved as you’ve described. I had no knowledge this was not standard back in the old days and that lenses with this feature were branded as “auto”. I am familiar with the lens stopping down to the selected aperture as the shot is taken. I believe the camera performs the same action for stop-down-metering method (Pentax - Green Button) with manual focus/aperture lens. I have no experience with old (60’s-70’s) lenses and never realized there were an even more manual lenses back then. Thank you for your clarification. Cheers!!!