FD Lens (Rear) Cap

I'm not old, but I feel old when I think about film cameras... I never really got into shooting with film. I got into photography with a Minolta DiMage 7, and I graduated into Canon EOS cameras. But I have in my possession an old Canon AE-1 SLR film camera, and two lenses; the Canon brand 50mm FD lens, and an accompanying 28-135mm Vivitar FD lens.