From the 20mm/3.5 Ai review:In 1967, Nikon introduced the Nikkor 20mm/3.5 UD lens, and they made about 40,000 of these wide angle lenses. Optically, these lenses were not great. In 1974, Nikon replaced it with the 20mm/4 which took 52mm filters but had similar optical performance. In 1977, Nikon introduced the lens in this review which returned to a maximum aperture of f/3.5 and had better optical performance. About 28,000 were produced.
In 1981, Nikon discontinued the Ai version and replaced it with this lens which was discontinued in 1984, only three years later. About 28,000 units were made.
This lens performs well on a short extension tube allowing for extremely close focusing and dramatic macro shots, or reversed on a bellows for much greater than 1:1 magnifications.
macro, mounted with a PK-11 extension tubemacro, mounted with a PK-11 extension tube (detail)macro, mounted with a PK-11 extension tube (detail)
This lens exhibits coma and has an infrared hot spot at f/22.
comainfrared hotspot at f/22
Color fringing of the corners. Also, some spherical aberration is present.
color fringing at f/3.5, corner detailcolor fringing at f/5.6, corner detail
This compact 20mm's front element does not turn as it is focused. It has all metal construction with excellent focus action having no play in the focusing collar. This Ai-S version has a shorter focus throw than the Ai version at only 70°. Like its predecessor, there is a focus and depth of field scale as well as an infrared focus index. Focus stops at infinity (∞).
Focal length: 20mm
Maximum aperture: f/3.5
Minimum aperture: f/22
ø52mm filter ring
Lens construction: 11 lens elements in 8 groups
Picture angle: 94°
Distance scale: 0.3m/1.0ft. to infinity with infrared focus index
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