And now I find out that it seems to be a rather rare prototype lens a friend of mine and member here told me, which hasn't been made often, computed in 1975 and made by GOI in St. Petersburg, the Russian State Optical Institute. Mine is from 1991.
It has Pentax-K bajonet mount and supposedly a 7e/6g lens design (I found on a russian site) - but my finding is, that it actually is a 8e/5g design, confirmed by 10 strong reflections I see (equals 5 lens groups).
My lens looks like this:

It has quite a nice modern multicoating (my lens is made 1991):

Here now a size and look comparision with the Carl Zeiss Jena Sonnar electric f2.8 200mm, to show how compact it is:
























