I haven't seen this particular lens, but the Leitz projection lenses that appear to be similar are not Petzvals, they are triplets. 90mm may / should cover 6x6, but with projection lenses the question is what format they were intended to project. I have found some of that focal length that were intended for 35mm projection and they don't do a very good job with 6x6. Others do. Trial and error is your best guide, I'm afraid.