In 1959 Nikon Introduced the Nikon F SLR Camera and with it a range of "Nikkor" lenses utilising a brand new lens mount. This mount is the same physical fitting as used today some 40+ years later. During this time there have been several modifications to the mount to reflect the changing needs in terms of the data passed between lens and camera. Below is a concise description of how to tell which type is which and what type fits what.
The original lenses pass information from the aperture on the lens to the camera body, to tell the camera's light meter what aperture had been set. This allowed the diaphragm to remain wide open during metering and the viewfinder to remain bright. Pre AI lenses pass this information by using a pin which protrudes from the camera body and mates up with a fork which is mounted on the aperture ring of the lens. When mounting a pre AI lens on a camera body it's aperture ring must be indexed to that body before it can successfully be used. This can be done by mounting the lens (some cameras require the aperture to be set to F5.6 in order that the pin and fork mesh together properly, others couple automatically as the lens is indexed) then turning the aperture ring all the way to minimum aperture and then all the way back to maximum aperture. The lens is now indexed and ready to use.
When discussed or advertised lenses of this age may be called scalloped lenses, this is because of the distinctive scallops cut into the aperture ring. Sometimes they are also referred to as Nikkor-H, Nikkor-Q, etc., this is how many of these Pre-AI lenses were marked, the letters standing for the number of elements used in the construction of the lens. The letters used are as follows:
AI (Auto Indexing) lenses changed the way the aperture set information was sent to the camera body. On AI lenses a portion of the aperture ring nearest to the lens mount was cut away to reveal a notch. When mounted on the camera this notched portion of the aperture ring comes to rest against a small spring loaded lever protruding from the camera body. As the aperture ring is rotated to give a smaller aperture the notch moves the lever to indicate how many stops the aperture has been closed down. AI lenses also have a second aperture scale marked on the aperture ring, these are there so that the aperture setting could be viewed through the viewfinder via a small window positioned at the top of the viewfinder looking down onto the second aperture scale.
Some Pre-AI lenses have been modified to facilitate AI coupling conversions. Most conversions are very good quality, a few amount to nothing less than butchery. Of the former variety look out for scalloped style lenses with AI couplings or scalloped lenses with the later knurled style aperture rings. Poor conversions are filed or cut out sections of the Pre-AI mount, hopefully accurately positioned but not always.
AIS lenses maintain all the features of AI lenses but utilise various arrangements of metal protrusions surrounding the light path but inside the lens mount. These transmit information to the camera facilitating the use of Shutter Priority and Program Mode on some of the early cameras to offer this feature. AIS lenses also have a small grove machined out of the back of the lens mount; when the lens is attached to a compatible camera this grove uncovers a pin allowing it to protrude from the cameras lens mount. This tells the camera that the lens is compatible with Matrix Metering. In addition to the machined grove AIS lenses can also be identified as such by the minimum aperture which is always coloured orange. NB a few AI lenses also had an orange minimum aperture on their main aperture scale but AIS lenses have this indicator on both the large and small aperture scales.
E series lenses were built as a budget alternative to the AIS lenses and share much of their compatibility with the AIS models. They have no pre AI metering fork and make use of much more plastic in their construction, also the glass used in E series lenses is only single coated instead of the usual multi-coating as used on mainstream Nikkor lenses.
AF (Auto Focus) lenses, as the name suggests, allow a compatible camera to automatically set the focus distance on a lens. This involves two additions to the lens mount, firstly the addition of electronics into the lens. These not only aid auto focusing but Nikon cameras started to use these electronics in order to achieve shutter priority, program, and matrix metering compatibility. Evidence of electronics in the lenses can be seen by the electronic contact pins visible on the inside of the lens mount adjacent to the aperture ring. The second addition to the lens mount was a drive shaft that made a connection from the auto focus motor in the camera body and the focusing mechanism in the lens. Auto focus lenses maintained compatibility with all the functions facilitated by AI and AIS lenses with the exception of the fork used by Pre AI Cameras and lenses (and the loss of the detailed depth of field indicating system). If you look at the aperture ring of an AF lens there are two small dots in the plastic molding which are in exactly the correct position for the screws that hold the Pre AI forks in place. Although the author has never seen an example it would seem logical that Nikon were able to convert these aperture rings by adding the fork. AF lenses also marked a shift in the construction of Nikkor lenses. Until the introduction of AF lenses nearly all Nikkor's were of metal construction, however the new AF lenses were mainly plastic using metal parts only where necessary, making for lighter, more affordable but sometimes less robust lenses.
P (Program) lenses are manual focus AIS lenses that have the electronic contacts found on AF lenses. This allows them to be used on cameras which rely on the electronics for part or all of the camera's metering. P lenses do not have a Pre AI fork.
D lenses are AF lenses equipped to transfer focus distance data back to the camera. This "three-dimensional flash and metering technology" is used by matrix metering on cameras which support the extra function offered by these lenses. In every other respect a D lens is the same as a normal AF lens.
G lenses are similar to D lenses but with one very important difference. On a G lens the aperture ring is completely absent and all control of the aperture must therefore be electronically adjusted via the camera. This makes G lenses unusable on all manual focus and some auto focus camera bodies.
AFI lenses are AF lenses but instead of using a motor in the camera body they have their own motor built into the lens itself. AFI lenses share the same compatibility as regular AF lenses with the exception that some older AF cameras cannot provide auto focus via this method.
AFS lenses are similar to AFI lenses except the lens' internal motor is silent in operation. These lenses like most modern Nikkors have the AFS designation on the lens' name plate located on the barrel of the lens. These lenses also have ten electronic contact pins instead of the five found on regular AF lenses.
DX lenses have a smaller coverage circle than other Nikkor lenses. This is to provide digital SLRs using the APS sized sensor to benefit from small more affordable lenses better corrected for use with digital sensors. So far all DX lenses have been of the G lens design. DX lenses can be identified by the DX on the lens' name plate.
Exceptions to the rule
Shift Lenses are preset lenses, this means that as well a click stop calibrated aperture ring they also have a smooth turning ring which stops the aperture down to the desired point as preset on the click stop ring.
Mirror Lenses do not incorporate an adjustable aperture and are therefore only usable at a single aperture: their maximum.
Medical Nikkor lenses are very easy to spot as they have a built in ring flash. They are designed specifically for close up work, originally, as the name suggests, for the medical profession. There is no meter coupling between the lens and camera body as the aperture is automatically set to balance the built in flash.
GN Nikkor A special purpose lens of Pre AI design that allowed the guide number of a flash gun to be set on the lens and the focusing ring and aperture ring to then be locked together. This meant that as the lens was focused the aperture would automatically be set correctly for the flash-to-subject distance.
Nikon F3 AF Lenses. The F3 AF was Nikons first attempt at producing a production auto focus camera. Two lenses were produced for the F3 AF: the 80mm and the 200mm. These lenses use motors in the lenses and not in the camera body but this made the lenses quite bulky, and Nikon soon abandoned this approach and opted for the more familiar design used in their mainstream AF system
New manual focus 50mm F1.8. This is an AIS lens which is missing its Pre AI fork, with a more plastic based build quality.
New manual focus 70-210mm F4.5-5.6. Pictures of this lens show it to be missing its Pre AI fork and build quality appears to be similar to the 50mm mentioned above.
There are a few other exceptions, mainly early lenses, for example the original Micro-Nikkor was of preset design. The 2.1cm F4 and some of the fish eye lenses, as well as having manual diaphragms, required that the camera mirror be locked up and an external viewfinder be used, so that the camera could accommodate the deep protrusion of the rear lens groups. There were also pre production lenses and one offs made from time to time and also specially modified equipment for organisations such as NASA who have used a wide range of Nikon equipment over the years.