Well, it says it in the name of the lens what size it is meant for - it was made to cover at least whole plate (6.5 x 8.5 inches), so it should have a focal length with both elements combined of at least 180-210mm (maybe as long as 240mm, but not likely) and an image circle of at least 270 mm, probably closer to 300mm. The Protars are also convertibles, so individual cells will be longer in length and have different (larger) image circles than both elements combined. As to value, you can do an ebay search on closed listings to try and get a sense of value. There are also several forum members here and over on Large Format Info who can give you a good idea of value, but it would also help to have pictures of it to be sure.