Had a browse at a local cash converters (a good source of old camera gear in the UK) and saw a Pentacon 50mm F1.8
. I don't need it at all but at twenty pounds I was never going to leave it there. I could possibly recover the purchase price through selling the M42 to Canon adapter that came with it. Anyhow; obviously not as sharp as current lenses (thankfully!), MFD of 0.33m and the bokeh looks good to my subjective eye. I posted a few images with a 50mm Tessar above this post; I found this lens is better than that. Establishing a year of manufacture is difficult, even with a serial number (mind you, some of these lenses didn't even have that) and Googling doesn't make things any clearer. I know Pentacons were made in East Germany between 1968 and 1990 but that's about all. No matter - it's a lovely lens.
to see EXIF info for this image (if available)