300mmf/4.0 has no diaphragm actiongreenspun.com : LUSENET : Canon FD : One Thread
Recently purchased a nice 300mm f/4.0 with the new FD mount for use on my 1970 FT. Lo and behold, the diaphragm doesn't work: no way, no how. Other lenses I'm using: a 28mm f/2.8, new mount, and an older 200mm f/2.8 with the original FD ; both lenses work fine and stop down all the time. Is the 300mm's diaphragm shot? Or is massive and expensive internal surgery needed to repair it, making the purchase a definite bummer? I am hoping that it's a camera/lens issue, but since the other two lenses work just fine, I don't think so.
-- Jack Szymanski (email@example.com), July 17, 2001
I once lost a diaphragm control spring in my FD 300/4.0 L. Repair cost with full CLA at Professional Camera Repair in New York City was about $85. Well worth the price, in my opinion.
-- David Goldfarb (firstname.lastname@example.org), July 17, 2001.
Jack, as David mentions, there is a spring in there. Someone with a 300/4L once told me that the spring had come unhooked in his lens. Oily residue may separate from the grease in the lens, and can make its way to the diaphragm blades, causing them to hang up. I've cleaned a couple of 50mm lenses with oily diaphragms, with great success. A CLA may well solve your problem.
-- Alan Swartz (email@example.com), July 19, 2001.