One additional comment: The Industar-50 was a camera lens. A version intended for use on enlargers, the Industar-50U, was also made. I'm sure the I-50 (no U) can be used on enlargers, but it might be suboptimal in various ways. (I've seen claims that glues and lubricants used in camera lenses can soften under the heat produced by many enlargers, for instance.) I don't know offhand what the design of the I-50/I-50U was (number of elements, coatings, etc.), but I strongly suspect it's either a 3- or 4-element design. The I-50 was used on cameras in the 1950s and 1960s, so its coatings, if any, would be simple by modern standards. I'm not sure when the I-50U was manufactured. You'll probably get significantly better results stopping down to mid-range than using it fully open or at its smallest aperture. Used 6-element lenses are pretty inexpensive on eBay and will probably produce better prints than the I-50/I-50U. You can decide whether it's worth tracking down a better lens once you've tried the I-50/I-50U.