I think the 635 has the 3 element taking lens rather than the 4 tessor type found on some D and the upper end Mats such as the 124. Given that the camera you are looking at is complete $100 seems like a good price. Stopped down to F 8 you will get a fair image. I had a 635 years years ago, like mid 70's, found it in a pawn shop. Got rid of it as my Nikon with 105 lens was much better than the 635 80mm, and my Yashica's Ds and 124 were better in 6X6.