One of the rudimentary issues of getting engaged in buying old Nikkor lenses is understanding the designations. The information below was gathered from Wikipedia and is maintained there at the following link: http://en.wikipedia.org/wiki/Nikon_F-mount This is a wonderful source of information and I hoghly encourage checking out the full article on WikiPedia. Please be kind to Wikipedia and help support them as an information resource!
Nikon has introduced many proprietary designations for F-mount Nikkor lenses, reflecting design variations and developments both in lenses and the F-mount itself. There are also "unofficial" designations used by collectors and dealers to differentiate similar lenses.
Nikon F professional SLR camera with eyelevel prism and early NIKKOR-S Auto 1,4 f=5,8cm lens (1959)
A typical F-type ("Pre-AI") lens, the Nikkor 50mm 1:1.4 showing "Nippon Kogaku Japan" engravings, scalloped-metal focus ring, and old-style Meter Coupling Prong (clearly visible to the top right of photo).
Nikon F2SB professional SLR camera with GN Auto Nikkor 1:2,8 f=45mm AI lens
A typical AI lens: A Nikkor 50mm 1:1.4 showing "Nikon" engravings, rubber focus ring, and new-style Meter Coupling Prong distinguished by its cutaway sections. The lens is mounted on a Nikon FE2 camera.
A — Auto Nikkor (also unofficially F, Pre-AI, Non-AI or NAI) — Designation for the first generation of F-mount lenses, introduced in 1959. These were all single-coated, and meter coupling was provided by a prong (known as the Meter Coupling Prong) fixed to the lens's aperture ring. The Photomic T through-the-lens light meter introduced in 1965 worked at full aperture, so the maximum aperture of the lens had to be communicated to the meter by mounting the lens with the aperture ring set to f/5.6, and then turning the ring to first the minimum and then the maximum apertures. (The need for this step was eliminated by the AI system below.) Early versions are marked "Nippon Kogaku Japan" and have their focal lengths stated in centimetres, but models produced after about 1965 have focal lengths stated in millimetres. The "Nippon Kogaku Japan" engraving was replaced by "Nikon" from 1971 onwards.
Warning: Mounting a non-AI lens can damage many modern Nikon camera bodies. AI-cameras that still may use non-AI lenses includes the Nikon
F2A/F2AS with Photomic A (DP-11) or AS (DP-12) finder, Nikon (Nikkormat) EL2, as well as Nikon FM and FE. In addition, the Nikon Df, a DSLR introduced in late 2013, can use non-AI lenses. The A lenses can be converted to the AI specification; see AI'd below.
T, Q, P, H, S, O, N, UD, QD, PD — Appears immediately before or after the "Nikkor" name on F-type lenses (see above), designating the number of optical elements in the design. Short for Tres (3), Quattuor (4), Penta (5), Hex (6), Septem (7), Octo (8), Novem (9), UnDecim (11), QuattuorDecim (14) and Penta-Decem (15). The terms Unus (1) and Bini (2) were also apparently designated, but never used. Terms P=Penta, H=Hexa, and PD=Penta-Decem (greek root) were used (instead of Quinque, Sex, and QuinDecim) to avoid ambiguity with Quattuor, Septem and QuattuorDecim. This designation scheme was dropped with the introduction of "Modern" (K-type) Nikkors in 1974.
Auto — Designation for F-type lenses indicating an automatic diaphragm (aperture). Not to be confused with automatic exposure or auto focus, the designation fell out of use in the early 1970s and was not carried onto K-type lenses.
C — Indicates a multicoated F-type lens. Appears with an interpunct after the number of optical elements (in the form "Nikkor-X·C"). This designation was introduced in 1971 and discontinued in 1974 with the introduction of "Modern" (K-type) Nikkors, when multicoating had become standard practice.
K — "Modern" or "New" Nikkors introduced in 1974. While Pre-AI for compatibility purposes, K-type lenses introduced the new cosmetics that would be used from 1977 onwards for AI-type lenses (see below). The scalloped-metal focus rings were replaced with rubber grip insets, and the use of element number and coating designations was discontinued. The 'K' designation itself is believed to be derived from the Japanese "konnichi-teki", loosely translatable as "modern" or "contemporary".
AI — Manual focus with "Automatic Maximum-Aperture Indexing," introduced in 1977. The AI standard adds a Meter Coupling Ridge to the aperture ring, which encodes the current aperture setting relative to the maximum, and a Lens Speed Indexing Post on the mounting flange, which encodes the maximum aperture itself. The Ridge and Post couple to the camera's light meter. Lenses designated AI-S, Series E, and AF all include these features of AI. Current professional Nikon camera bodies link with the Meter Coupling Ridge, but the Lens Speed Indexing Post is ignored and the maximum aperture value is set electronically by the operator instead. AI-designated lenses also improved on the original Meter Coupling Prong, adding cutaways which allow more ambient light to fall on the aperture ring, increasing visibility on cameras which optically projected the setting inside the viewfinder.
AI'd — An unofficial designation for lenses converted partially (Meter Coupling Ridge only) or completely from non-AI to AI. This is accomplished by replacing the aperture ring and the metering prong (using a long-discontinued kit procured from Nikon) or by modifying the original part. Some independent camera repair technicians continue to offer such conversions.
AI-S — The successor to AI, the AI-S specification added two mechanical enhancements — standardized aperture control, and the Focal Length Indexing Ridge — required for the shutter priority and other auto-aperture exposure modes of the Nikon FA, F-301/N2000, F-501/N2020, and F4 cameras. Later cameras did not require these features, and interoperate with AI and AI-S lenses identically. The term AI-S is now commonly used to refer to manual focus lenses, and Nikon continues to produce eight prime lens models in its AI-S line. All Nikon AF lenses with aperture rings (non-G) also meet the AI-S specification, except for their lack of a Meter Coupling Prong (which can be added).
Standardized aperture control. AI-S lens apertures move in a standardized fashion in relation to their stop-down levers. The levers of AI and pre-AI lenses were intended only to close the aperture to its manual setting. The advance of aperture control by the camera body itself, by partial actuation of the stop-down lever, meant more precision was required for consistent exposure. This feature is indicated by a Lens Type Signal notch in the lens mount. Although later Nikon cameras cannot control the apertures of AI-S lenses as the F4, they control the apertures of AF lenses using the same method of partial lever actuation and standardized response.
Focal Length Indexing Ridge. AI-S lenses with a focal length of 135mm or longer are indicated by a ridge on the lens mount, used by FA, F-501, and F4 to engage high-speed-biased Program Autoexposure.
- Aspherical — Aspheric lens elements. Also Hybrid used: Thin molded aspheric elements coupled to a conventional glass element. This designation appears in specifications but not lens names.
- CRC — Close Range Correction. Improved performance at close focus distances. Achieved by internal focus movements that move differently relative to the movement of the other focusing elements. This designation appears in specifications but not lens names.
- DC — Defocus Control. DC lenses have a separate control ring for spherical aberration, which affects primarily the appearance of out-of-focus areas, also known as bokeh. At extreme settings, DC lenses can generate an overall soft-focus effect. Includes only the AF DC-Nikkor 105mm f/2D and AF DC-Nikkor 135mm f/2D.
- ED — "Extra-low Dispersion" glass incorporated to reduce chromatic aberration. Lenses using ED elements usually carry a gold ring around the barrel to indicate the fact (although on some low-end lenses gold foil is used instead), and older lenses were also marked "NIKKOR✻ED". In addition to normal ED glass, "Super ED" glass is used in some lenses.
- FL — Fluorite. Designates a lens which includes one or more elements constructed of fluorite instead of glass. Currently includes only the AF-S 800mm f/5.6E FL ED VR, available since 2013, and the AF-S 400mm f/2.8E FL ED VR, available since 2014.
- GN — Guide Number. Assists in flash exposure on cameras without automatic flash metering. The flash's guide number is set on the lens, and the aperture is accordingly coupled to the lens's focus ring for correct exposure. The only GN lens, the supercompact GN Auto Nikkor (it was the second smallest Nikon F-mount lens ever made), was built during the late 1960s and early 1970s.
- HRI — High refractive index elements. Contains elements with a refractive index >2. This designation appears in specifications but not lens names.
- IF — Internal Focus. Focusing is accomplished through the movement of internal lens groups, eliminating extension and rotation of the front lens element, allowing focus to be driven quickly by a small motor. IF lenses also allow the use of a polarizing filter without the need to readjust it after focus.
- Micro — Micro-Nikkor lenses are capable of high reproduction ratios, typically 1:2 or 1:1, for macro photography. The first Micro-Nikkor lenses were created for producing microforms of Kanji text.
- N — Indicates the Nano Crystal Coat, a relatively new type of lens coating that originated in Nikon's semiconductor division. Lenses with this coating feature the logo of an "N" inside an elongated hexagon on the name plate.
- NIC — Nikon Integrated Coating, a proprietary multicoating. Appears in specifications but not lens names.
- PC — Perspective Control. Lens features shift movements (and also tilt movements on some models) to control perspective and depth-of-field. Newer PC lenses are designated PC-E (see designation E above). Not to be confused with early lenses marked "Nikkor-P·C" meaning a five-element coated lens (see pre-autofocus designations above).
- PF — Phase Fresnel. To counteract chromatic aberration. It replaces several lens elements, thus reducing the size and weight of a lens.
- Reflex — Designates a catadioptric (mirror) lens.
- RF — Rear Focusing. Quite similar to internal focusing. Focusing is accomplished through the movement of rear lens groups, eliminating extension and rotation of the front lens element, allowing focus to be driven quickly by a small motor. RF lenses also allow the use of a polarizing filter without the need to readjust it after focus.
- SIC — Super Integrated Coating, a proprietary multicoating. Appears in specifications but not lens names.
- UV — Lenses designed for imaging ultraviolet light.
- VR — Vibration Reduction. Uses a moving optical group to reduce the photographic effects of camera shake. Some VR lenses also support a panning mode, detecting horizontal movement of the lens and minimizing only vertical vibration. The second generation of VR is called VR II, which is designed to offer another 1-stop advantage over original VR, but lenses with this feature are still designated simply "VR."
- Bellows — Lens designed exclusively for use on a bellows unit, primarily for macro photography. Also called short mount. Since some Nikon bellows allow for a front rise, they allow a limited variety of lenses to be used similarly to a PC lens (see Optical design above).
- Medical — Nikkor designation for a macro lens with a built-in ring light strobe system, designed for clinical and scientific applications.
- Noct — "Night." Specialty low-light lens designed for maximum sharpness at the widest aperture setting. The name has been applied only to the Noct-Nikkor 58mm f/1.2.
- UW — Underwater lenses. Produced for the Nikonos systems.