Compur shutter size on Super Angulon 8/75greenspun.com : LUSENET : Large format photography : One Thread
I have a dead Synchro Compur shutter on a Schneider Super Angulon f/8 - 75 mm. The shutter size, after Schneideroptics, is 0-1.
I'd like to find a replacement, but in the same time I wonder whether I could use a shutter from an Angulon (said size 0 ) to fit my 75 mm lens?
-- karl herrebout (firstname.lastname@example.org), April 07, 2001
While I'm not fluent in these calculations, I believe the following logic is correct.
A size "0" shutter for an Angulon is made for a 90mm lens. (Schneider webpage.) While the 75mm lens may fit the shutter, you will need to increase the f-stop on the 90mm shutter by 20%. (1.2=90/75.) This is an effective decrease in aperture of 0.526 stops, or call it a half-stop for close enough.
So, you can use the shutter. But, allow a half-stop less light to reach the film than is implied by the reading on your meter.
The reason for this adjustment is that, to get the same amount of light, the diameter of the aperture must be 20% larger for a 90mm lens than for the 75mm lens, because the 90mm lens is 20% further from the negative. So, based on the f-stops on the lens intended for a 90mm lens, the aperture diameter will be too large for the 65mm lens, and must be reduced in size.
-- neil poulsen (email@example.com), April 07, 2001.