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Got this from my girlfriends father, along with a Chinon CE-4. I've tried searching it up, and found a lens with very similar looks and specification, called Carl Zeiss Jena Vario-Prakticar 35-70 f/2.7-3.5.
I have not used it much, but got it down from the shelf when I put film in my A3 (my A50 and M28 are both on holiday for the summer). All-metal construction, two-touch.
From test shots on my K20D, it seems like it is weakest at the wide end, and better at 50 and 70mm. At 70mm, there is a 'macro' mode, which enables focus down to 1:2,4. Seems quite sharp, especially stopped down a bit.
Very prone to flare (no hood), or rather 'total loss of contrast' when a strong light source is shining on the front element.
As I'm generally curious, does anybody know anything about it?