Pekka Buttler, 08/2022
The table below summarizes the lens’ key specifications:
|Brand:||Nikon (Nikkor)||Lens name||AF 20 mm 1:2.8|
|Focal length(s)1||20 mm||Angle-of-view2||94°|
|Maximum Aperture||f/2.8||In Production||1989–1994 (AF)|
|Lens mount||Nikon F||Subfamily (if applicable)||AF and AF-D|
|Length3||43,0 mm||Diameter4||69,3 mm|
|Filter ring diameter||62 mm||Weight||272 grams|
|Lens element count||12||Lens group count||9|
|Aperture blades (S/R/C)5||7 S||Focus throw||110 °|
|Minimum focusing distance||25 cms||Maximum magnification||1:8,3|
|Has manual aperture ring||YES||Has Manual focus ring||YES|
• AF and AF-D versions are identical except that the AF version (without D) does not communicate distance information.
• These lenses (AF and AF-D versions) are fundamentally the same lens as the Nikkor Ai-s 20 mm f/2.8 introduced in 1984 (data sheet here).
• To improve close-up performance, Nikon used its floating elements, ‘close-range correction’ (CRC) technology.
• Should one want to use filters, low profile filters are recommended, and stacking filters will lead to hard vignetting.
• The dedicated lens hood is the HB-4 (bayonet mounted), and – due to the lens’ propensity to vignette when using thick filters – thread-mounted OEM hoods are potentially troublesome.
A brief genealogy of Nikon SLR lens types
Nikon is undoubtedly one of the great names in 35 mm SLR photography. The Nikon F mount has been in continuous production since 1959. During that time, the mount has developed/changed in some detail, however without ever fully sacrificing compatibility.
In short (a longer version is here), the development of Nikon’s SLR lenses can be traced as follows:
• 1959–1977: Pre-Ai. Manual focus lenses that use ‘rabbit ears’ to communicate selected aperture with the camera body.
• 1977–1986: Ai and Ai-s. Manual focus lenses that may have ‘rabbit ears’ for backward compatibility, but are designed to communicate selected aperture with the camera body through indentations in base of aperture control ring.
• 1986–today: AF and AF-D. Autofocus lenses that do not have a focusing motor within the lens, but rely on the focus motor within the camera. All AF and AF-D lenses are simultaneously Ai-s lenses (they are Ai-s lenses extended with AF) 6
• 1996–today AF-S and AF-P. Autofocus lenses that have an internal focusing motor and do not rely on the body having a focusing motor.
Nikon has a long history of producing non-intrusive Ultra-wide angle lenses. While Nikon offered various f/3.5 and f/4 20 mm lenses between 1967–1984, the Ai-s 20 mm f/2.8 was Nikon’s first ultra-wide with a f/2.8 maximum aperture. That design was – with only minor tweaks – reused in the subsequent AF and AF-D versions.
The current AF-S 20/1.8 (2014–today) and Z 20/1.8 (2020–today) are based on more modern designs.
Besides adapting, this lens can be used natively on all current high-end Nikon dSLRs and several earlier medium-to-high-end older Nikon dSLRs. Moreover, if the camera body contains a slot-drive focusing motor, this lens will even auto-focus7. Likewise, if the lens has been retrofitted with ‘rabbit ears’, it can be natively used on all Nikon F-mount film cameras ever produced (without the rabbit ears, it is limited to post 1977 bodies).
Thanks to being a fully manual lens (manual aperture, manual focus), the lens can be adapted to all mirrorless cameras using a suitable dumb adapter (and such adapters are easy to find). Moreover, a large range of special adapters (helicoid adapters, tilt/shift adapters, speed boosters) for using Nikon F lenses on most mirrorless systems are available. Currently no adapters for mirrorless exist that would allow autofocus through the slot-drive screw.
Using Nikon F lenses on non-Nikon SLRs and dSLRs is likewise a distinct possibility. Thanks to the relatively generous flange focal distance of the Nikon F mount (46,5 mm), adapter rings for all dSLR mounts are available as well as for a goodly portion of film-era SLR mounts. Such rings will not allow autofocus, and are unlikely to support auto aperture, but even then the lenses can be used in stop-down metering mode.
1 Focal length is (unless stated otherwise) given in absolute terms, and not in Full-frame equivalent. For an understanding of whether the lens is wide/tele, see ‘Angle-of-view’.
2 Picture angle is given in degrees and concerns the diagonal picture angle. Rule of thumb:
> 90 ° ==> Ultra-wide-angle
70–90 ° ==> Wide-angle
50–70 ° ==> Moderate wide-angle
40–50 ° ==> ‘Standard’ or ‘normal’ lens
20–40 ° ==> Short tele lens
10-20 ° ==> Tele lens
5-10 ° ==> Long tele lens
< 5 ° ==> Ultra-tele lens
3 Length is given from the mount flange to the front of lens at infinity.
4 Diameter excludes protrusions such as rabbit ears or stop-down levers.
5 S=straight; R=rounded; C=(almost)circular at all apertures.
6 There is a further sub-class of AF-D lenses called AF-I lenses that are otherwise AF-D lenses (meaning, fully Ai-s compatible), but have an internal focus motor. Only long tele lenses were made in AF-I variants.
7 As of this writing, the following Nikon dSLRs fully support autofocus, aperture priority and manual metered modes on Nikkor AF/AF-D lenses: D2, D3, D4, D5, D6, D200, D300, D300s, D500, D600, D610, D700, D750, D780, D800, D800E, D810, D850, D7000, D7100, D7200