A while back I read a chart wich would give the correct F- stop setting based on near to far standards movement. In other words focusing on the nearest point th en measuring the distance on the monorail to the farthest point entering that di stance to a scale which would gine me the proper F stop. Since purchasing the Ro denstock Studio calculator I have learned that monorail angle and repro ratio ar e also factors. My problem is that the Rodenstock calculator is"based on a Circl e of C.. of .03mm for 35mm.IYO is this sufficent for large enlargement? Are ther e other scales out there? I use 4X5