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 via a manual setting on the ASA dial.
The Nikkormat FTn and FTn metered finder for the Nikon F introduced semi-automatic aperture indexing which was achieved 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.

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 Ri
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 via a manual setting on the ASA dial. The Nikkormat FTn and FTn metered finder for the Nikon F introduced semi-automatic aperture indexing which was achieved 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.
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 Ri
Nikon F-mount