I have recently purchased two 150mm copy lenses that have been remounted in shut ters. The aperture scales were done by two different people (before I purchased them). Now, I was curious if the aperture scales would agree, so that I could match the better lens with the better shutter, and then sell the other.
Well, they don't agree, there is a visibly different aperture at the same settin g on both lenses. I don't have the original barrels, so I can't determine the c orrect aperture off of them.
Any recommendations on how to see which one is correct? I thought I might set u p a shot with a third lens, meter a spot on the gg, then change to the lenses in question and see which one agrees (all at the same aperture, of course). I don 't have a third 150, but I do have a 180 than I can use, and I'll try to meter a subject that is very uniform so that there is little chance for metering deviat ion.
Does this work? I think it should, as long as I work at the center of the I.C., and don't have any extraneous light from the back.
As a side note, I assume that when you have a lens mounted in a shutter (by Sk G rimes, etc) they don't apply a formula to determine the aperture. They measure off the iris in the barrel, right? How do they do it if they don't have the ori ginal iris, or if the existing iris is suspect (as in my case)?
Any thoughts would be appreciated.