I've been a professional Nikon user for going on 40 years and have never sold any old equipment. I own 16 old Nikon film cameras from the original F models through to the F5 and F100. The reason I stuck with Nikon when making the jump to digital is I am able to use ALL my old Nikon glass, literally dozens of lenses from fisheye to long telephotos and many zooms. I love using my old 55mm f1.2 non AI lens for portraits on my D7100 and on my D700 for low light. You can meter with the Nikon digital cameras and there is a focus assist indicator in the extreme left lower corner of the viewfinder. All you have to do to meter is go into the menu settings, go to Setup Menu then Non-CPU Lens Data. Then assign the lens a number, enter the focal length and enter the maximum aperture(lowest number) and press OK. Your Nikon digital camera will now meter in Aperture priority or manual exposure. There is an exposure meter in the center of the lower viewfinder to show correct, over or under exposure. Try it, it works great! I have read that the only thing inferior about the older lenses are the modern coatings. These older Nikkor lenses are all glass and metal, not like the cheap plastic G lenses. Read some of the reviews on Ken Rockwell's site of older Nikkor lenses. You can pick up these older lenses reasonably cheap.

Yes. A number of us do do this, and yes they are better for 'art' rather than a replacement for modern lenses. Probably the hardest to adapt are Canon R/FL/FD/FDn to Canon EOS DSLRs, but it can be done. It works better with APS-C than FF EOS DSLRs. An adapter with a lens is relatively easy, and some get very good results, I have gone down the path of using replacement mounts, which is more expensive but has no intermediate glass. Mirrorless cameras are likely a good way to go for old FL glass, without needing intermediate glass.

In addition to old Canon glass I also have old Contax/Yashica lenses, a Russian Helios, and soon an old Micro Nikkor lens to use on our Canon cameras. Just had it re-lubricated and bought an adapter.

They all have a place, and many of these lenses have value which is increasing. They are fun to use when time and subjects permit.

I have no experience with FF Canon DSLRs so thanks for your additional input on the subject. Not all Pentax manual lenses have that lever to control aperture, but it is no doubt a good idea if the lever is present to insure that it does not interfere with the camera's mirror.

These levers do not interfere with the mirror in the crop sensor Canons I have used but it would probably be wise to check for interference on any Canon Camera if the lens has the lever.. Thanks again for the heads up.