Okay, I was incorrect in when the ef mount was introduced but for the most part Nikon lens with an F mount still work on the majority of their digital bodies without any type of adapter or modification. A canon fd lens needs an adapter to work with the canon digital bodies.
Still a plus if you shoot Nikon.
Of course there is a big difference between a lens mounting on the body, and actually working correctly. IIRC with the older mechanical F mount lenses modern DSLR bodies do not have the mechanical linkages to allow the aperture to be operated. So you are stuck with no stopping down, since the aperture stays open when you remove them from the body. Also unlike Canon you cannot put a Nikon body into Av mode and have it set the correct exposure on lenses without electronic apertures. Canon bodies will set the correct shutter speed with either a fully manual adapted lens, or actually no lens at all. The same deficiencies apply to Pentax and their development of the K mount. I shot Pentax K mount when I shot film, the first new SLR I owned was an ME Super that I got as a present Christmas 1980. I moved to Canon when I went digital when I realised that the Pentax K mount lenses I had would not work with any of the Pentax DSLR's then on the market in 2005.
It probably made sense to keep the original mount form factor when AF was being first introduced, it meant that the technology could be changed slowly at first. It does though mean that as the evolution continues you reach the point where you have a new mount species anyway, that loses the backwards compatibility. When that new species has the same name though it does cause much confusion. That has actually lead to the point where even some of the lenses with features like AF will now not work with the newer bodies. Good luck with the Nikon alphabet soup you need to untangle to know if a specific lens will actually function on any particular body. Even if they are all F mount.
Oddly FD lenses are some of the hardest MF lenses to adapt to the EF mount. This is mostly because the FD mount is as large in diameter as the EF mount, and both mounts have just about the shortest registration distance for the 35mm format. So you end up having to move the lens forward a bit, and so need to have an optical element to get infinity focus. Having both a very large diameter mount, along with a very short registration distance, is an advantage when adapting lenses in other mount types though. So the Canon EF mount can actually be adapted to use a wider range of other mount lenses than any other mount in the 35mm SLR format world. Of course the "mirrorless" cameras can do even more mount type conversions, since they have such short registration distances you have plenty of room for conversion.
Alan
