I've just fitted my Schneider-Kreuznach Super-Angulon 90/1:8 lens to my quarter-plate camera - the 90mm focal length is *just* usable on it, but if I remove the rear lens element from the Compur 0 shutter then I can increase the focal length. I've not actually tried this yet, and I know that I will sacrifice some sharpness doing this, but my question relates to aperture / exposure. If I do this what do I need to know about this will affect the f/stop at the new focal length? Presumably once I measure the focal length I can work out the new f/stop based on what it was as a 90mm? Is there anything else I need to know about the lens in this manner? PS: I'm aiming to use this camera and lens for alpine photography.