Film photography is making a comeback nowadays. You can find it in a few specialized stores across major cities around here (all the classic film rolls, Kodak, Fujifilm, Ilford, etc). I got into film photography only recently, I have an Olympus XA but lately I have been thinking about getting myself an SLR (probably a Spotmatic) since I have already a decent collection of vintage lenses (mostly M42).
This is an Industar-50 and yes, M42 bayonet, maximum aperture of 16 and minimum of 3.5.
50mm focal lenght but bare in mind than when adapted to a mirrorless croped sensor camera as mine it becomes the equivalent of a ~75mm.
I have as well an older version of this lens (from 1959) with a M39 bayonet (I posted it a few pages ago).
It is a nice little lens especially for the price since you can get these for like 20€ in Ebay and it is great for street photography and low contrast shots if you like your images to come out with a vintage\nostalgic look. It is surprisingly pretty sharp too for a lens of this size (the only thing I am not really a fan of is that setting the aperture on this lens can be a little clumsy sometimes since it is so small).
Carl Zeiss produces amazing lenses. The Jena model you tried is their vintage "entry-level", a classic nonetheless. There are other models like the Carl Zeiss Distagon that produce amazing images. You can't go wrong with Zeiss glass.
Some film photos that I did with my Olympus XA:
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