Canon 24mm SSC lens - aperture question

I just picked up a 24mm 2.8 Canon S.S.C. lens and the aperture is

behaving a strangely. When I use it on my A-1 body, the aperture

closes down when I take the shot, but doesn't open up again until I

cock the shutter. On my FTb body, the aperture closes down as soon

as I mount the lens on the body. As I adjust the f-stop ring, the

lens closes down or opens up as if I'm using a depth of field

preview. Any idea what's up? Thanks.

There's a good chance that the Automatic/Manual Aperture Lever is locked fully counterclockwise. Move it clockwise so it looks like the lever (1) in the picture at this link: http://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/earlyfdlenses/index.htm

 

If that's not it, one of internal springs or levers may have come unstuck and it will require servicing.

 

Cheers,

Ben,

 

Look at the lens mount with the lens in its on-camera position, i.e., with the focus index mark at 12:00.

 

At the bottom of the mount is the stop-down lever, which I believe you'll find latched to the right, at about 4:00. Push it to the left to unlock and it should fall to 6:00. Your problem should be solved. I tried this with my FTbn and A-1 and was able to duplicate your problem.

 

This detent is a neat feature of the older FD lenses that allows easier use on a bellows or extension tube. The New FD lenses require the Manual Diaphragm Adapter to accomplish this trick.

 

The A-1's behavior is its normal routine for setting the aperture prior to exposure. We normally never see it happen, though, because the diaphragm is closed last, after the camera presets it, by the stopdown lever.

Thank you Duane and Alan - you were right. The stop-down lever was moved counter-clockwise, sitting at 4 o'clock. I moved it to 6 o'clock and everything works great. Cheers.