Hello Cameramakers annd Richard Knoppow, I have a 2 questions regarding establishing F-stops on a lens. First, I'm looking for suggestions on how to determine the stop settings on a lens of known focal length, having an iris with no markings. This came up a while back and Richard, I think I remember what you said which is scary for me, but here goes. I think I recall that the "compression" effect of having the iris between the groups could be worked out by putting a point source well behind the lens, and a groundglass as close as possible to the front of the lens, then measuring the dimeter of the illuminated circle on the groundglass. Did I get that right? In other words, on a 160mm lens, a circle diameter of 10mm would indicate the f16 setting and so on. I also remember less well some suggestions using light meters. I would appreciate comments on this problem.
The second problem is a lens that has no iris at all, and no practical way to install one. I have a big iris that will fit on either the back or the front of the lens. I am pretty certain installing the iris this way will cost me a lot of coverage, but on this lens I may have it to spare. Would the stops in that case be just the aperture divided by the focal length? Gene Johnson _______________________________________________ Cameramakers mailing list [EMAIL PROTECTED] http://rmp.opusis.com/mailman/listinfo/cameramakers
