View Full Version : Ross Airo 20" f6 lens group spacing

Tony Kearney
14-Sep-2016, 23:57
Hi, I recently bought the front and rear lens groups for a Ross Airo 20" f.6 lens from a deceased estate. Looking around the web I think it might have been salvaged from a an F52 Aerial Photography Camera as it has military markings.

Anyway, the groups appear to focus on infinity when touching each other and even focus on infinity if spaced 300+mm apart so I'm wondering if the spacing between the groups will be critical, especially as I'm not planning on assembling them into a tube with an Iris or waterhouse stops. Does anyone know where I might find the correct spacing between groups (if there is such a thing) or the best way of determining what that might be? In the short term I'm thinking of setting up a telescoping tube with a group mounted on each end and a focusing screen so that I can check for focus and barrel distortion, but if there is an easier mathematical formula, I would be more than happy to hear from you.