The W Rokkor 21mm lenses are a series of three prime wide angle lenses produced by Minolta for Minolta SR-mount single lens reflex cameras. The first 21mm lens released was the W Rokkor-PI 21mm f/4.5 (1962), which featured a symmetrical design similar to the contemporary Zeiss Biogon. This was succeeded by the W Rokkor-QH 21mm f/4 (1963), with slightly improved speed and similar symmetric construction. The third and final 21mm lens was the MC W Rokkor-NL 21mm f/2.8 (1971), which featured a retrofocus design that did not require the reflex mirror to be locked up, allowing use of the built-in viewfinder.
Minolta updated the design several times during the course of production; the first two versions were symmetric designs which required the reflex mirror to be locked up, while the third version was a retrofocus design, followed by a cosmetic update in 1973.
When the Rokkor-PI was introduced, it was advertised as "a product of much painstaking work and research by the company's technical staff", which Erhard Bertele called "a mockery" in retrospect, declaring it "[an imitation of the Biogon] with seemingly insignificant small changes to the original Bertele design". The similarities in lens design between the Biogon and the Rokkor-PI have led to speculation the latter was discontinued in favor of the Rokkor-QH in response, as the -QH shares a similar 8-element, 4-group design as the Nikkor-O 2.1 cm f/4 (1959). In 1964, the suggested retail price of the Rokkor-PI , with accessory viewfinder and leather case, was . By 1968, the successor Rokkor-QH retailed at a lower price, , with a dealer cost of .
The Rokkor-NL , introduced in 1971, has three floating elements to compensate for focusing aberrations at close range. It was replaced by the MD Rokkor 20mm lens (1977), which was more compact and lighter.