I am new to this Forum. I have been shooting digital Nikons for many years and had taken a break from film for the past couple decades. In that time I have collected over 50 film cameras (about half are working) and have been getting back into film photography. I mainly shoot Nikon and have many older and newer F-Mount lenses. I have found an issue while doing some experimenting with testing film versus G lens combinations. I recently put my Nikon 500mm PF f/5.6 lens on my F5 and F100 cameras and neither camera would allow me to change the aperture (tried in Manual and Aperture priority). All other functions seemed to function properly. After checking various other G lenses including 24-70 f/2.8, 105 f/2.8, Sigma 50 and 35 f/1.4 and many others I found that the Nikon PF 300 f/4, 200-500 f/5.6, and 70-200 f/2.8 FL lens do not allow any aperture adjustment and seem to be stuck at a stopped down position. Has anyone else experienced this and are there any suggestions. Thank you for any answers.