NIKKOR - The Thousand and One Nights No.43

The NIKKOR-Q.C 13.5cm f/4

In this, the 43rd tale, we will once again discuss a NIKKOR lens designed for use with the Nikon S Series. In tonight's tale we cast our minds back to the Japan of the immediate postwar period-–an era that spawned the very first NIKKOR 35mm film format lens. Why is there such fascination with occupied Japan, and what kind of era was it that produced this NIKKOR lens?

Here, we will unravel the mysteries of the NIKKOR-QC 13.5cm f/4 and shed some light on this lens, which dates back to the beginning of the NIKKOR range.

by Haruo Sato

I. The fascination with occupied Japan

The term "occupied Japan" refers to Japan in the seven-year period immediately following World War II, from 1945 until 1952, when the nation was under the occupation rule of the U.S. government through GHQ. Between 1947 and 1952 products that were manufactured in and exported from Japan were required to bear a stamp reading "Made in Occupied Japan" or "Occupied Japan." This period of was one of poverty in which even food was in short supply. However, out of necessity, the Japanese had to earn foreign currency and support the economy by means of "Occupied Japan" products. Some of these "Occupied Japan" products were shoddily made or simply souvenirs. However, since this production period only lasted five years and since virtually all such merchandise was shipped to the United States, products marked "Occupied Japan" have become collectors items-–and this not only applies to cameras. The era has lent these products added value.

There are also Nikon cameras and NIKKOR lenses that bear the "Occupied Japan" stamp. These NIKKOR lenses featured improvements to prewar designs and incorporated the glass materials that were available. It was in fact a NIKKOR-QC 13.5cm f/4 that David Duncan purchased, instead of the NIKKOR 8.5cm-–the lens with which he had fallen in love, as related by Mr. Oshita in Tale 36. The story goes that Mr. Duncan bought the lens after establishing in a projection test that it was superior to German-made lenses. He left behind many photographic masterpieces shot using it.

II. Development history

Let's explore the development history of the NIKKOR-QC 13.5cm f/4. It was Saburo Murakami who came up with optical designs for NIKKOR lenses for use with the S and L Series. Mr. Murakami belonged to the Optical Research Laboratory, Research Department (Ashida Laboratories). The tools at his disposal were limited to logarithm charts, abacuses and hand-operated calculating machines such as Tiger calculators. He designed numerous high quality lenses in an era when this required not only intellect but also perseverance. He was an outstanding and abundantly talented designer who could quite legitimately be described as a Japanese Bertele.

A report written to mark the completion of the design of the 13.5cm f/4 lens came out in the autumn of 1946.

Immediately after this, the company came out with a NIKKOR lens with an L-mount, as used at the time by Canon Camera and Nippon Camera.

The arrival on the scene of Nikon S-mount lenses would have to wait until the launch of the Nikon I in 1948. Mass production of the NIKKOR-QC 13.5cm f/4 commenced in October 1946. It is not known exactly when the lens was released; however, it has been established that advertisements for it were appearing by October 1949. The initial lenses featured a unique filter diameter; however, this was subsequently upgraded to 48mm diameter. Mr. Murakami was also instrumental in improving the design of this lens by changing the relative aperture to f/3.5, and in making the lens barrel lighter. This NIKKOR 13.5cm f/3.5 would make its mark as a standard NIKKOR lens for the S Series.

III. Imaging characteristics and lens capabilities

Let's first take a look at a cross-sectional diagram of the lens. The lens is a typical Tele-Sonnar lens and boasts a simple and logical three-group, four-element structure, with a convex lens on the left, cemented convex and concave lenses in the middle, and a convex lens on the right. With its asymmetrical aperture, it is classed as a telephoto lens. Accordingly, its overall length is short compared to its focal length. These Tele-Sonnar lenses, with their thick walls, are characteristically long and thin, with a small front-lens assembly and a small filter diameter designed to keep the incident light rays closer to the optical axis. In technical terms, the entrance pupil can be disposed closer to the object. In terms of aberration, the lens is prone to pin-cushion distortion on account of its asymmetry and does not do such a good job of correcting chromatic aberration of magnification. Although the lens exhibits excellent spherical aberration correction, the difficulty inherent in controlling the variations in spherical aberration corresponding to different colors shows itself in the lens' tendency to over-correct spherical aberration at short wavelengths (from blue to bluish purple). This is due to the simplicity of the lens's structure. The degree to which the lens can control this type of aberration is dependent on the designer.

What kind of pictures does the NIKKOR-QC 13.5cm f/4 take? Let's consider this question based on both the lens's aberration characteristics and the photographic results.

First, let's read the design report. As regards aberration correction, the main features of this lens relate to spherical aberration and field curvature. The lens under corrects for spherical aberration, resulting in a pleasing background blur. In addition, since the field curvature is relatively large, the lens under corrects both the sagittal image (S image) and the meridional image (M image). In particular, the M image is greatly under-corrected, resulting in a considerable degree of astigmatism. In addition, under-correcting the S-image surface serves to suppress sagittal coma flare. Although this technique sacrifices the flatness of the image plane slightly, it avoids the "blurry" images caused by flare.

The images formed by point sources of light are shown in a spot diagram. The focus of the point images is good for the center of the lens, indicating that sharp images will be formed.

However, as the image height increases, there is a gradual tendency toward front focus, due to the low field curvature. There is little flare; however, resolution drops off slightly toward the periphery of the image. The meridional coma flare is slightly greater than the sagittal coma flare.

In terms of overall imaging characteristics, the center of the image produced by the lens is sharp and of high resolution, while there is a tendency for the resolution to drop off toward the periphery of the image, due to front focus resulting from the field curvature. As the point images do not undergo any unnatural transformation, the lens seems to produce images that are unaffected and devoid of any quirks. Notably, the low field curvature produces a pleasing blur (bokeh) quality in the image background. A nice and simple blur quality can be expected, coupled with a tendency for the bokeh to increase closer to the edge of the image. The lens is also good at correcting for distortion (which is supposedly difficult to correct for), with the level of distortion being around 0.6%.

Next, let's take a look at the photographic results of this lens. At f/4 (full aperture), the central area of the image exhibits high resolution and relatively good contrast. From the center outward toward the edges, the image progressively softens and the resolution declines slightly, in line with the tendency toward front focus. However, the lens produces soft fault-free images without any unsightly rivers running through them, and offers apparently higher resolution than is suggested by the design values. Stopping down to 5.6 improves the sharpness of the central area of the image and increases the area of the image that appears sharp. The periphery of the image is also improved, becoming sharp enough to qualify as part of the high-quality region of the image. Stopping down to f/8-f/11 extends the high resolution area to the periphery of the image and produces a consistently high image quality throughout the entire picture. The contrast level is also just right, with images that are rich in tonal gradation, as opposed to exhibiting a stark two-tone contrast. When the lens is stopped down to f/16, the shape of the point images becomes uniform; however, the overall sharpness is reduced due to the effect of diffraction. For the sharpest results, it is probably best to stop the lens down to f/8 or f/11, while the f/4 aperture setting is probably best for shooting portraits.

Let's take a look at the lens' imaging characteristics by examining some example photographs. The first example is a portrait. As demonstrated by the texture of the hair and eyelashes, the resolution and contrast are just right, yielding a natural-looking image that is rich in gradation. Also noteworthy is the splendid bokeh of the background. The photograph has a melting-like blur effect, which is probably another reason why Mr. Duncan favored this lens.

The second example photograph is a backlit snapshot. It was shot with the lens stopped down, producing a quirk-free image with a consistent sharpness that extends right to the edges of the picture. It is worth noting that the image does not exhibit the aforementioned "two-tone" high contrast level. It is clear that although the image was backlit by a flood of light from the clear sky, even the dark areas of the image have been well reproduced and the level of contrast compression is appropriate.

IV. A copy or an original?

Tonight's tale does not include any designer biographies-–it simply describes a 35mm-format NIKKOR lens whose design bridged the prewar and postwar periods.

In 1947 there were two departments in Nippon Kogaku (present-day Nikon) that were responsible for optical design. One was the First Design Department, which designed ordinary photographic lenses. The other was the Ashida Laboratories, which conducted design research into difficult-to-manufacture lenses-–in particular high-speed lenses. In 1947 Mr. Murakami left the Ashida Laboratories to become section chief of the Fourth Mathematics Section of the First Design Department. The 13.5cm lens that is the subject of tonight's tale was probably the last lens that Mr. Murakami designed at the Ashida Laboratories.

The calculation method of the day was work-intensive and involved the use of logarithm tables, abacuses and hand-operated mechanical calculating machines to perform the calculations for each individual ray of light.

It is said that at the time it took 10 minutes to calculate the passage of Rand rays (parallel rays from an infinite distance incident on a lens) through a single lens with two curved surfaces.

This was fast for the time. It was normal to order 20 minutes worth of calculation for the ray tracing for a single two-surface lens. The recipients of these orders were the mathematics sections, which were dubbed the "math girls," as they consisted solely of women. This was not an official organizational name, but rather seems to have been a moniker that is more in line with the present-day team spirit ethos. More than 20 young women, working in pairs, would labor day-in day-out, performing calculations. For the designers of the day, being surrounded by young women represented an enviable working environment. The reader may be wondering, however, if these teams were really comprised solely of women. In fact, there were also "math boys" in Nippon Kogaku. The "math girls" and "math boys" competed with one another in terms of calculation time and accuracy. For some reason, however, women were judged to be better at this work.