I have a circa 1880s Dallmeyer RR that has an orignal waterhouse stop with it stamped f22 that is 5/8" in diameter. That would suggest a focal lenght of 11 3/4". However the lens focuses at infinity at about 25". The lens has the name, patent info and "25x21" stamped on it. The lens is mounted on an vintage 18x22" camera and has plenty of coverage for it. It is all brass, about 8" long by 4" in diameter and in almost perfect condition. Anyone have any information on the lens, type or FL?? Did they use the US system then? If so how would I calculate the proper stops.