Lomo MIN-4 is a nice, vintage polarising microscope. Lomo MIN series microscopes use the same objectives, so for example those from MIN-4 fit MIN-8 and vice versa, and even Lomo Polam polarizing microscopes.
Here you can see similar LOMO MIN-5 model: http://www.mikroskopfreunde-nordhessen.de/dateien/Min-5.pdf
The photos show my microscope from 1958 :) If you need any parts to repair the LOMO-MIN-4 microscope, please contact me.