Gordon Yee , Apr 13, 2008; 08:51 a.m.
Henry, the "FD" designation on your 500mm lens indicates that it should have the signal devices needed to communicate with FD bodies. The camera knows that the maximum aperture is f/8. Because the aperture is fixed, none of these signal devices should move or change. Your AL-1 should meter correctly with this lens in its normal aperture preferred mode.
My understanding is that, with non-FD lenses, the AL-1 will meter properly only if you stop the lens down manually before taking the picture. There is no provision on the AL-1 to do this. Even though FD and FL lenses have the same aperture lever, you still need to close the aperture manually on an FL lens to get proper exposure. If you're using a non-FD lens that does not have the ability to close the aperture manually, I don't think you can get proper exposure on the AL-1.
In stop down mode, the AL-1's aperture priority AE simply selects the correct shutter speed at the time of exposure based on the scene's brightness. Because of its fixed aperture, there would be no difference between automatic and stopped down metering with the FD 500mm mirror lens on an AL-1.