At long last I have mounted the lens by The English Lens Co. of London on my Calumet monorail and it looks to be an interesting lens. By focusing the lens to infinity and measuring from the Waterhouse stop slot to the front of the ground glass I have calculated that this lens is 195mm. Is this the correct way to calculate the focal length? I now want to make a few Waterhouse stops and I believe that there is a formula to calculate the hole sizes once you know the focal length, but I can't find any information about this formula. As the lens cost £10 UKP and the camera cost £30 UKP I'm not prepared to send the lens anywhere to have stops made, I want to do it myself! Thanks in anticipation.
Pete.