NIKKOR - The Thousand and One Nights No.6

OP Fisheye-NIKKOR 10mm F5.6

The 4th and 5th Tales discussed popular lenses, the Zoom-Nikkor Auto 43-86mm f/3.5 and the AI Nikkor 105mm f/2.5. This time we'll take a look at a rather special lens, the OP Fisheye-Nikkor 10mm f/5.6.

by Kouichi Ohshita

I. The world's first orthographic projection fisheye lens and aspherical SLR lens

The history of fisheye lenses at Nikon is quite old, beginning with the 16mm f/8 fisheye (180 degrees) in 1938.
In March 1957, two years before the release of the Nikon F, this lens was upgraded to the Fish-eye-NIKKOR 16.3mm f/8 lens, and built into a Weather photography system (Weather Recording System) using 120 format B/W film.

This camera was capable of capturing the sky-image above the horizon in a single shot, and we widely used for meteorological observation by the Meteorological Agency, National Defense Academy and NHK (Japan Broadcasting Corporation).
From September 1960 this system became available in our Japanese catalogues as the "Camera with Fisheye Nikkor".

Since then, there have been 13 general product releases in this line: the 8mm f/8 sold as a interchangeable lens for the Nikon F in 1962; the Fisheye-Nikkor 7.5mm f/5.6 with improved brightness, sold in 1966; the R-UW AF 13mm f/2.8 for the NIKONOS RS AF, the world's first underwater AF fisheye, in 1994; the Fisheye Type 20mm f/8, one of the "Amusing Nikon Lenses" sold only in Japan (Nippon) in 1995; and the FC-E8 fisheye converter for the COOLPIX line of digital cameras (1998).

Of these, the OP Fisheye-Nikkor 10mm f/5.6 (called the OP Fisheye below) was released in 1968 as the fourth fisheye lens from Nikon, following the 7.5mm f/5.6.

The outstanding feature of the OP Fisheye was its orthographic projection design, the first interchangeable lens of its type in the world.
As shown in Fig. 1., the equidistant projection method used in prior fisheye lenses like the 8mm f/8 and 7.5mm f/5.6 resolved the image on the film so that the light beam angle of incidence was proportional to the image height (distance from the image center).
The orthographic projection OP Fisheye, on the other hand (Fig. 2.), resolves the celestial image onto the film.

In simple terms, the OP Fisheye has a larger central image than other fisheye lenses, and the image at the periphery is smaller.
When compared to ordinary photographic lenses, the distortion is even greater than with conventional fisheyes.
With orthographic projection lenses, the area occupied by the plane source in the image is proportional to its brightness at the object.

The lens was originally developed for scientific research applications such as brightness measurement and architectural illumination.
It is extremely difficult to implement this type of orthographic projection fisheye as a spherical lens, so the OP Fisheye makes the front lens aspherical to provide accurate projections.
The OP Fisheye was not only the world's first orthographic projection fisheye lens, but also the first aspherical SLR lens in the world.

II. Lens composition

As shown in Fig. 3, the OP Fisheye is composed on nine lens elements in 6 groups.
Design was handled by MATSUKI, Keiji, who was then in the 1st Research Section. MATSUKI also worked on the Fisheye-Nikkor 6mm f/5.6, making a major contribution to the development of fisheye lenses at Nippon Kogaku K.K.

And incidentally, the animation at the top of the page (AI Fishye-Nikkor 6mm f/2.8) is by SHIMIZU, Yoshiyuki, introduced in Tale Five (AI Nikkor 105mm f/2.5).

The basic lens composition of the OP Fisheye is the same as the 7.5mm f/5.6, but a large-diameter aspherical front lens is used to achieve orthographic projection.

Briefly, the lens has two concave lens elements to reduce the 180-degree view, a cemented lens to correct the resulting aberration, and a 5-element convex lens group consisting of a turret-type filter, stop, and a concave lens group to resolve the image onto the film. Even by today's standards this is a very rational lens layout, and Nikon fisheye lenses since have following this basic design.
The front aspherical lens of the OP Fisheye, as evident from Fig. 3. and the photo of OP Fisheye-Nikkor 10mm f/5.6, are visibly aspherical.
This is a key feature of the external appearance of the lens.
There are better processing technologies these days, but back then, direct-molding technology has made it easier to volume-produce small-diameter aspherical surfaces, but careful finishing was required after grinding. NC (Numerical control) machine tools can now fabricate aspherical surfaces easily, but then craftsmanship was an important part of every lens.
Lens design also had to assure that the image resolution performance would not be degraded even if the aspherical surface was imperfect. Aspherical lens mass production technology, while productivity was much lower than it is today, still existed.
And through these design and manufacturing processes, the first aspherical SLR lens in the world was born.

III. Photography with the lens

Let's try few shots.
The rear lens protrudes from the mount, so it has to be mounted on an SLR that lets you lock the mirror in the up position, like a Nikon F or F2.
An external viewfinder DF-1 is used to frame the shot, and this is the same finder as used with the 7.5mm f/5.6 lens. Even if you look through this finder, however, you cannot see the unique image created by the OP Fisheye. When you first try it, you will be quite surprised at the difference between what you see in the viewfinder and what you see on the film. It takes a little time to get the hang of.

The maximum aperture is f/5.6, which is a rather small aperture, but the image resolution is extremely sharp even to image corners. It has no focusing mechanism, and the focal length is a short 10mm, so there is no out-of-focus even with close objects. The image will be adequately sharp up through about 50cm (1.6 ft.) from the lens even at maximum aperture.

This also means, however, that dust and marks on the front lens will show up clearly in the image, so you must protect the front lens against dust and damage. This is the same for all wide-angle lenses with large front lens, not only fisheyes, but at any rate cover the lens when not in use, and carry a blower with you at all times. Work to keep it clean.
The fisheye lens has a wide picture angle, making it difficult to shoot without including strong light sources, but the OP Fisheye (although it only has a single-layer coating) can be used with confidence because it does not suffer from severe ghosting even when the sun is in the image directly.
Since years have passed since the lens was manufactured, colors are slightly yellowish, but as you can see from the samples, not severely. There should be no practical problems with used with reversal film.

The OP Fisheye was released in 1968, and disappeared from the shelves in about 1980, when the Nikon F3 appeared. Perhaps because it was designed for special applications, only a relatively low number were made in spite of being available for over a decade...... well under 1,000 units, I believe. We will probably never know for sure just how this special-application lens came to be created, but I wonder if the secret behind its uniquedesign and the resolution to the volume-production problems inherent in the aspherical lens wasn't the zeal of a developer who wanted to expand the potential of photography, and make possible new types of photographs. While the lens was originally developed for scientific applications such as measurement luminosity, its unique pictures are exciting in snapshots, too. The smooth lines of the aspherical lens still speak of the many difficulties my predecessors faced developing and manufacturing it.