somebody help me out here please. I just made a lens change and need some advice. First of all I'm no math whiz so I'm looking for an answer not a formula... I will however take a formula. I might have to work it backwards though. Here is the problem. I salvaged a shutter off an old kodak camera. The glass is set up for a 100 mm lens. I am in the process of attaching the shutter to a barrel lens I have made. Now here come the problem. The shutter at 100 mm had a top aperture of 32.. that shutter and aperture is now on a lens of 135mm. Someone tell me what the new aperture will be. From my pinhole calculator Im guessing f45... Does that sound about right.