Ultra-wide-angle lens made by Nippon Kogaku, Nikkor-O 21mm f4 for the Nikon S series. Released in 1959. Optical construction consists of 4 groups and 8 elements. Serial number is 621xxx (the first three digits are not unique identifiers). Distance scale is in meters.

While the Nikkor 21mm f4 for Nikon F mount is relatively common, the version for Nikon S mount is extremely rare, with only 298 units said to have been produced.

The included dedicated viewfinder is constructed with 5 groups and 5 elements. Its serial number is 600xxx. Made of plastic, it is lightweight. Originally, a deep rear cap was provided specifically for this finder, equipped with a mount to securely hold it in place. A rare item.

This item was previously sold by our store and has now returned to us after being well cared for by its owner.
It appears to have seen active use in its time, as the barrel shows minor scratches, scuffs, and some paint loss from handling. The protruding rear section also has visible wear on the painted surface, but there are no prominent dings or deep scratches.
The lens surface shows several fine cleaning marks on the front element and noticeable deterioration of the coating, but no haze is present. Actual shooting tests revealed little to no impact on image quality.
The included viewfinder has paint loss and linear scratches on the eyepiece. The plastic parts show some glossiness due to aging, but the glass is clean and provides a clear and bright view.
Test results were excellent. Please take a look at our sample gallery. There is noticeable vignetting, but the center delivers impressively sharp rendering that catches the eye.

When mounted on a well-used Nikon S2, SP, or S3, it creates a highly attractive appearance. A rare and collectible lens that's enjoyable to use and admire.
Comes with front and rear caps and a filter. The filter has a small dent, and the rear cap is a third-party replacement.