Copal shutter f markings

A dumb question from a newcomer to the joys of large format. I've recently acqui red a Schneider Tele-Xenar f 5.5 240 mm for a 4x5 wooden field camera. The Copal No. 1 shutter does not have f markings, though there is a blank tab where these would normally be. The brochures I've scoured suggest Copal shutters never have these markings, and don't have the automatic attachments of Compur shutters. An d unlike the Compur, the Copal does not have click divisions on the f lever. Cou ld someone tell me what is the easy way to work out the various f stops? Many th anks. Jonathan Manthorpe, Hong Kong.

Generally the lens manufacturer supplies a plate which is calibrated to show the right f-stops for the lens - since any number of different lenses can come in a copal 1 shutter. Your lens may have been remounted in the shutter. You can probably work out approximate f-stops by measuring the iris opening as seen from the front of the lens - full open is f/5.5, when the iris opening is half of full, that's f/11, and so on.