This is a focal length and size that can be hard to come by. It is marked 4" focal length, which agrees with what I saw using a piece of paper and the window. Rear glass is about 30mm, so it is around f3.4. It has a smoothly working focus knob AND a flange. Flange diameter is about 2 3/8", so this will fit on a very small board. Glass is uncleaned but looks ok. I've had a lot of petzvals, but never one as small and light as this one at 4" AND with a flange. Weight is around 200g. Image circle looks about 4", so usable on a 4x5 but a little small. Price: $135 shipped in the USA, USPS money order preferred, paypal ok. % to apug is sold here.