NIKKOR - The Thousand and One Nights No.50

Focusing Unit and NIKKOR-Q Auto 400mm F4.5

The 1964 Tokyo Olympics were an event to be remembered for the opportunity it presented for a major player with SLR press cameras to take center stage. This tale introduces the super-telephoto lenses that were that leading role.

by Kouichi Ohshita

I. The Olympics and press cameras

Until around 1950, Graflex's Speed Graphic large-format camera was the most popular press camera. As even photo studios are using digital cameras these days, large-format cameras have become quite rare. However, those who know even a little about this type of camera will likely wonder how these cameras, with which the photographer covers himself and the rear of the camera with a black cloth to focus, could be used for on-site press coverage. It is important to remember that press cameras like the Speed Graphic had a design that differed greatly from that of the large-format cameras used by photo studios. Speed Graphic cameras could easily be folded into a compact box for storage and transport in a bag or satchel, and were equipped with built-in rangefinders and viewfinders. These cameras supported quick and nimble framing and focusing, and did not require use of a black cloth or tripod. At the time, one good shot of an event or incident was sufficient for newspapers. Speed Graphic large-format cameras offered immediate development of each film sheet, handling of negatives was easy without the need for enlargement, and large frames also left room for cropping. For newspapers, these cameras offered the flexibility needed in the battle over minutes and seconds.

In the late 1950s, rangefinder cameras like the Nikon S and those introduced by Leica began to gain popularity with press photographers.

This is due to improvements in 35mm-format camera systems, including improvements to film and automation of film development, as well as the sudden increase in demand for photos with the switch from space for just a single photo per article to space for multiple photos as more and more photographic magazines were being published. Roll-film cameras, with their peripheral accessories that included interchangeable lenses and flash units, were well suited to this sort of use. Even so, SLR cameras continued to play a supporting role.

This all changed with the 1964 Olympics. The Olympics are not just a place where athletes compete. They are also an event that tests the skill of photographers, as well as camera and lens performance. However, restrictions on photography at the Olympics are very strict, and places where photographers can move about freely are limited. These restrictions require photographers to use multiple interchangeable lenses, and increased demand for especially telephoto lenses capable of capturing close-up shots from a distance. At the 1964 Tokyo Olympics, only authorized photographers from each country were permitted to take pictures, and then only from specified areas of the stands. This type of situation is the special province of SLR cameras and super-telephoto lenses. With its release in 1959, the Nikon F came to the forefront of press photography, gradually increasing Nikon's share in this field.

II. Focusing unit

Why was the Nikon F able to acquire an overwhelming share among SLR cameras in the field of on-site press photography? While the camera's great reliability, Nikon's service organization that backed up press photographers, and a motor drive that enabled certain capture of decisive moments are often noted, the true deciding factor was the rich lineup of interchangeable lenses, especially a group of super-telephoto lenses of varying focal lengths. The focusing unit played a large role in the line of super-telephoto lenses. In 1964, Nippon Kogaku released a total of five telephoto and super-telephoto lenses for use at the Tokyo Olympics. They were the Nikkor-P Auto 300mm f/4.5, Nikkor-Q Auto 400mm f/4.5, Nikkor-P Auto 600mm f/5.6, Nikkor-P Auto 800mm f/8, and Nikkor-P 1200mm f/11. The focusing unit was used with all but the 300mm, which had the shortest focal length.

There were three major reasons for designing these lenses for use with a focusing unit. One was the switch to automatic apertures*1 with super-telephoto lenses. For automatic aperture, movement of the aperture coupling lever on the body must be transmitted to the lens aperture. However, as focal length increases, the aperture gets farther away from the camera body, making design of the mechanism extremely difficult. It would be a great advantage in terms of design if the same mechanism could be used for all lenses.

The second was adoption of a common and more efficient design. Super-telephoto lenses with which a focusing unit is used have a fixed barrel*1 with no moving parts. All movable mechanisms, including those used for focusing and to control aperture, are built into the focusing unit. Therefore, by adhering to specifications for the joint where the lens unit and focusing unit meet, efficient design is possible. Further, the ability to focus on tuning of optical performance with the lens unit and operation with the focusing unit must have been an advantage with manufacturing.

Finally, the third was common use with Bronica lenses. By replacing the focusing unit with one for Bronica cameras, these super-telephoto lenses could also be used with Bronica cameras. Naturally, the fact that focal length could be changed by simply switching lens units, and the ability to use the lenses with medium-format cameras by changing the focusing unit were likely a great advantage to users.

*1 The 1200mm was the only super-telephoto lens with which the aperture on the focusing unit regrettably caused vignetting in all four corners of the frame. Therefore, this lens was equipped with an aperture, and automatic aperture could not be used.

III. New and conventional focusing units

There are two types of focusing units, new and conventional. Conventional focusing units did not have a specific name. The new focusing unit, released in 1975, was named the AU-1.

Its design was changed to one that provided a better match with the lenses that formed the "new NIKKOR lens group" (those with a new design incorporating a black barrel and silver ring between the aperture ring and focus ring) as it was known in Japan.

With the conventional focusing unit, the user had to attach a dedicated distance scale for the lens used. With the AU-1, however, function was improved with engraving of 400mm/800mm and 600mm/1200mm on the distance scale, allowing switching by rotating a ring. The aperture ring was also moved closer to the body for an operational feel similar to that of other lenses. The AU-1 was also designed with a filter box for inserting 52mm filters on the rear end of the focusing unit. However, as functions were increased, the weight of the focusing unit also increased.

As neither conventional nor new focusing units have an aperture coupling prong, exposure metering is not linked. Further, due to structural problems, they cannot be used with the latest SLR cameras, including digital SLR cameras.

IV. The Nikkor-Q Auto 400mm f/4.5

While mechanical design of the barrel uses an extremely efficient focusing unit, there were great restrictions on optical design. The aperture is to the right of the fourth lens element from left in Fig. 1. A structure like this, with the aperture positioned on the imaging side of the lens, is known as a behind-the-lens diaphragm structure.

In order to preserve peripheral light, the distance from the front glass element to the aperture must be made as short as possible. What's more, as the same focusing unit is used for lenses with focal lengths from 400mm to 1200mm, the position of the aperture cannot be changed with each lens. Clearly, this presents significant limitations on design.

Optical design of the 400mm, 600mm, 800mm, and 1200mm lenses was the responsibility of Yoshiyuki Shimizu. To achieve optimal positioning of the aperture with each lens, parallel design by a single person was likely most effective, but the job must have made his head spin. If we look at the design report, we get an idea of the difficulties faced at that time. It seems to have been especially difficult to decide on aperture position with this 400mm lens. The report shows that after examination and comparison of five types of lenses, the type shown in Fig. 1 was the one finally selected.

Lens structure consisting of four elements, in the order of convex, convex, concave, convex, as in Fig. 1 is known as an Ernostar structure. This type of lens provides very good compensation for spherical aberration and coma. With this series of lenses, the 800mm and 1200mm lenses were designed to be as short as possible. Accordingly, the 400mm lens had to be designed to be longer. Therefore, the Ernostar structure likely provided greater leeway in terms of lens length and back-focus control than did a triplet or other telephoto structure. If we reproduce performance from lens data, spherical aberration and coma are well compensated, and performance is pleasing through the 6x6 format frame diagonal. However, while some curvature of field remains and focus position differs quite significantly at 6x6 format edges, these issues are barely visible and consistent rendering can be seen in all but the four extreme corners when used with the 35mm format.

The greatest weakness of this lens was surely axial chromatic aberration. Axial chromatic aberration occurs when different wavelengths of light (color) are focused at different distances from the lens so that even if some colors are in sharp focus, others are not. This results in the appearance of reduced resolution and generates color fringes around object outlines. In images captured with this lens, a red-violet fringe can be seen in portions that are in focus, but this seems to be hardly visible in images of low-contrast subjects captured with light coming from behind the photographer. However, it would likely be noticeable in images of high-contrast scenes, such as those that are backlit or include a light source. As axial chromatic aberration is a type of aberration that becomes more conspicuous as the focal length increases, it could not be eliminated until ED lens elements that reduce chromatic aberration were developed for super-telephoto lenses.

V. Lens rendering

As always, let's take a look at lens rendering using sample images.

Sample 1 is a photo of a beautiful black-winged stilt, known for its long pink legs. 400mm is said to be the standard focal length for super-telephoto lenses, and it is a focal length that offers great flexibility in capturing a variety of scenes, from birds and wildlife to sporting events.

While this lens offers excellent compensation for spherical aberration, we can see from the sample image that overall rendering is rather soft. As shorebirds move incessantly in their search for food, photos of them may be slightly blurred (the bird's head is actually a little blurry due to movement), but this may also be the result of axial chromatic aberration.

Sample 2 is a photo of an American wigeon. If we look at blurring of the grass in the foreground and background, we see that foreground blurring is somewhat rough, while background blurring is soft and smooth. This is because as distance decreases, the spherical aberration curve drops to slightly negative values (under-correction). In addition, do you see how edges in blurred portions in the foreground are slightly red, while edges in blurred portions in the background are slightly green? This is also caused by axial chromatic aberration, and while it is not very noticeable due to the fact that this photo was captured under thin cloud cover with the light coming from behind the photographer, it would often be troublesome if the scene were backlit or if a light source were included in the frame. To reduce this effect, the aperture must be stopped down to around f/8 to f/11.

Sample 3 is a photo of the stars. This photo of the famous Orion Nebula (also known as M42, 43) situated south of Orion's Belt in the Orion constellation has been enlarged to 400mm. As the photo was captured in a city, it is not as good as it could be. Thankfully, use of a light-pollution filter improved reproduction of the nebula. Just as we would expect from the lens that covers the 6x6-format frame, rendering is consistent throughout the entire frame from maximum aperture. However, axial chromatic aberration causes a red-violet fringe around bright stars, and the stars themselves are not as sharp as they could be. In addition, the reason illumination falloff is so noticeable in Sample 3 is that contrast was increased 2 to 3 times in order to make the stars and nebula more conspicuous. As with other samples, this lens preserves a large amount of light at frame peripheries and exhibits consistent rendering throughout the frame.

The series of telephoto lenses released the same year as the Tokyo Olympics were very well received. Not only were they widely used for sports photography, but they also contributed to the growing popularity of nature photography that included photography of birds and other wildlife. In 1975, a new focusing unit was released, and ED lens elements were adopted for the super-telephoto lens series (600mm to 1200mm). Only the 400mm lens discussed here continued to be manufactured with no change to its original design. This is likely because release of its successor had already been decided. In 1976, limited production of the Ai Nikkor 400mm f/3.5 ED IF began to coincide with the Montreal Olympics, and the lens was released to the general public in 1977. This lens was equipped with ED lens elements that reduced chromatic aberration, as well as an internal focusing (IF) mechanism that greatly improved focus operation. It was a revolutionary lens with which total length was reduced by more than 10 cm. Beginning with these 400mm and 600mm lenses, more and more super-telephoto lenses utilizing the IF mechanism, which offered great flexibility, were released. This was the start of the super-telephoto era.