I was reading the other thread and thought about the Bellows-Takumar that I have but seldom uses. It is a 100mm f4 lens with M42 screw thread but no focusing mechanism built in. I do have a set of bellows and uses it but I was wondering if anyone's been using this lens for anything other than taking macro or slide copying. Perhaps portrait or using it on medium format SLR? I think it has coverage for 6x6. Also does anyone know what kind optical formula this lens has?