I am in the process of making a model (paper) for a 4x5 camera after the Jon Grepstad camera design. I have been at the math for some time. I have read the various threads on the Forum fro page 1 to 42, am still absorbing and working the models provided by Doug Bartell, JBHarlan, and one other author on trapezoidal bellows, and Jon Grepstad’s information on bag bellows as well. I still have a few questions that I cannot find ready answer to solvethe problem

1. I plan to use a 150mm lens, with an option of a later addition of a 210 mm lens. Using the data for these lenses, iI get focal length at 150 and 210. When turned to inches, the length of the bellows should range from 195 to 285 mm. When adding the recommended extra length for loss due to folding, (30%) the-recommended length becomes 240 to 340 mm for the 150 and 210 lenses, or rounded off to 8 and 12 inches for the length of the bellows. Is this anywhere near correct?

2. My openings are 160x160 mm rear and 130x130 mm front. Will a 150x 150 rear opening and a 95 x95 mm front opening for the lenses be adequate? Or can I go to 90x90 for the front opening and 146x146 for the rear opening work?

3. The length of the “rod” for the movement of the standards is recommended at 13 inches by Jon Grepstad’s design. Can I use a shorter bellows, closer to the focal length of 196 and 286 mm?

Thanks for any advice or corrections?