It seems to me that you have an older lens without the "E-ring" that couples the aperture ring to the meter. If you look at your 80mm lens that works with the meter you will notice a ring fitted in which there is a screw that moves the meter coupling prong when the lens is mounted. Turning the aperture ring then moves the camera's metering prong. E-rings can be expensive, but for lenses with short aperture rings (80/2.8, your lens, 40/4 and maybe others) a small rectangle of rubber or metal or something else can be glued to the lens's aperture ring. This post might help:
(there was a url link here which no longer exists)
In that post, the pencil mark shows where the prong needs to be when the lens is mounted and its aperture ring is set to fully open (f4 in the case of your 50/4).
