As in some Takumar 1.4/50, one element of this lens is made of thorium-added glass, which has the particularity of yellowing if kept in the dark, and return to normal color after prolonged ultraviolet cure!
Carl Zeiss Jena Prakticar 1.4/50mm
Carl Zeiss Jena Prakticar 1.4/50mm, given by Pascal Prussak june 17th, 2013.
Given with a Praktica BC1, and 2.8/28mm and 2.8/135 Prakticar lenses. Body out of order, and sea sand in the helical threads...
And as this lens remained several years enclosed in it's bag, in addition to cleaning and replacement of the grease, I had to leave the thoriated element three weeks under an ultraviolet lamp (for tropical reptiles terrarium) before I could reassemble and use it. There are two versions of this lens, this one is the first, and on the second the labeling "Carl Zeiss Jena Prakticar 1.4/50 MC" is on the front.