I have a neighbor with some older lenses he used with Nikon film cameras and he lent me a Nikkor-UD Auto 1:3.5 20mm lens that worked well for him. I mounted it on my camera no problem, put the camera in M mode and once I took a couple of test shots got SS and f-stop set and snapped some shots. Now, I'm ready to take the lens off and I'm not finding a way to do so. I've had this camera since it came out and use a variety of lenses, but never one of this vintage - so what am I missing? I've tried at various f-stops, but don't seem to know the secret handshake. The two-pronged metal tongue on the lens seems to be running into a plastic tab on the camera. Feeling stuck. Any help out there?