This just came in today from auction purchase.
It a "lowly" K Mount SMC Pentax-M 1:2 50mm.
One of the most common of all SLR lenses, it was made in the days of match needle metering, for film cameras and before auto focus. It was the normal starter lens for the ubiquitous but venerable Pentax K 1000.

Lens was a bit dusty out of the box, and there was some fogginess internally, between the front lens groups and the rear lens groups.
The rear glass assembly unscrewed from the lens body easily, and it took mere minutes to polish out the fog and the dust with a cotton cloth and some breath moisture.

To test it out, I mounted the lens to my digital SLR Pentax K 100 D.
Since the lens has no "A" setting, it does not support Program mode.
I tried it out in several different metering modes, including full manual settings by guesstimation, with manual bracketing.
But I THINK the lens worked the best with camera set to "AV" for Aperture Priority, the aperture preset by me using the lens' f stop scale and the camera matching with an appropriate shutter speed.
Lens is manual focus, but I still had Focus Confirmation function with the camera body.

Inside shots were at ASA 800 emulation.
Outdoors I used ASA 200.

Here are some of the best of the results. To my eye, performance of lens was crisp and sharp, good color rendition. And even though I shot with the naked lens, no filter and no sunshade, I see no significant tendencies to flare or aberration.

A classic old lens, but still a good one.

Please click on thumbnails to see enlargement.
All images are ©2011 E.J.Kowalski.