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  6. Tale 21 : Nikkor-T 10.5cm f/4

Very affordable lens where Nikkor soul dwells Tale 21 : Nikkor-T 10.5cm f/4

Further to the tale nineteen ninth night, tonight, the NIKKOR lens for Nikon S range-finder camera will be touched on. This rare lens, which has fetched high prices on the market, might have been the first telephoto lens that Nikon designed to target a general consumer as a virtual customer. Nikon's commitment toward development of a reasonable-priced lens originates in this lens. A history of an affordable lens and its lens performance characteristics, which predecessors at Nikon put their hearts and souls into, will be introduced hereunder.

1. Who was the godfather ?

This lens has been called "mountain NIKKOR" among people interested in a photography. Of course, Nikon did not name it, but what a nice nickname it is, don't you think so? Probably, as this NIKKOR lens resembled the Leitz mountain Elmar lens, maybe someone began calling "mountain NIKKOR". However, a design concept of "mountain NIKKOR" was quite different from that of the original mountain Elmar. An optical design of this lens was worked out by, to tell the truth, as was the case with 8.5cm f/1.5, Mr. WAKIMOTO, Zenji. I found out that this lens with quite different performance characteristics was designed by the same optical designer, so, once again, I was really impressed with how well Mr. WAKIMOTO was versed in a photographic lens.

2. Development history

Let's thumb through a development history of Nikkor 10.5cm f/4. It was at the end of year in 1959 that design drawings for a commercial product were released. To my surprise, other than the S-mount lens, Exakta and Praktica lenses were planned at first. Much to my regret, however, the plan was aborted. It was in the springtime of 1960 just coming into leaf that a commercial debut of long-awaited Nikkor-T 10.5cm f/4 for use in S-type Nikon camera was made. This lens was a good buy at approximately half a price of 10.5cm f/2.5 lens with a suitably portable size. Optical designers wished if an ease-of-use telephoto lens of reasonably priced compactness and a light weight well suitable for portability while maintaining performance could have been designed. So-called three sacred treasures *1 in an interchangeable lens at that time meant to imply 3.5cm, 5cm and 10.5cm. Therefore, thanks to the commercial debut of this lens, a product line of an affordable version of the three holy durables (3.5cm f/3.5, 5cm f/2 and 10.5cm f/4) was achieved. When merchandising the affordable lens nowadays and in the past, a balance between performance and a price becomes significant. In Japan, we have an expression "low price and poor quality *2 ". Among cheap products here and there, in order to reduce a cost, there were nasty ones as if their qualities were reduced, too. We talked of this expression when products fell short of our expectations. But, Nikon's manufacturing was completely opposite to this expression. Traditionally, a philosophy or determination exists in Nikon where "an affordable product to be widely used by the general people should have a quality that rivals or surpasses a quality of high-end merchandise". Because a low-end product was a product that almost all customers were likely to get hold of. As for a lens, it was considered that this very product quality of the single affordable NIKKOR lens represented product qualities of all NIKKOR lenses. For satisfying all customers, optical designers had to work out very hard, so that a price was able to go well with performance. In some sense, this was rather more difficult test than developing a top-end product. Such the optical designer's determination that had exceeded the times dwelled in this lens. This determination was very nothing short of a design philosophy inherited ceaselessly along with a name of NIKKOR.

*1 Originally, as an emblem of succession to the imperial throne, the emperor of Japan has taken over mirror, jade and sword of the imperial family from the predecessor. These mirror, jade and sword have been called three sacred treasures. Nowadays, this expression is widely used to imply that three kinds of goods, items etc are emblematic of hobby, knowledge, activity, wellness, richness etc.

*2 After the world war two, Japan was completely devastated and Japanese people had had a hard struggle for a living. At one time of these hard days, export markets were flooded with made-in Japan cheap products whose qualities were very poor or nasty.

3. Lens characteristics and performance

Nikkor-T 10.5cm f/4 cross-sectioned view

Please allow me to further keep on a bit technical explanation. Kindly take a look at a cross-sectioned view. You can see that it is a typical triplet lens. The triplet lens was a generic name of an objective lens consisting of literally three single separated lenses of a positive, negative and positive.

This lens was a design solution of a minimum element that was able to improve the Petzval sum, two chromatic aberrations and the Seidel aberrations at the same time. Thus, this lens was a typical lens incorporated into a cheap compact camera. A textbook of optical designers gives a description of the triplet lens almost without exception. In other words, the triplet lens was a starting point of the objective lens. However, this lens had a constructional shortcoming, wherein this lens was not suitable for obtaining a wide angle and enlarging a lens diameter. On the other hand, when the lens was for use in a low-end medium telephoto lens with a moderate lens speed, the triplet lens was the very most appropriate lens. A choice of the triplet type of a few lens elements for this product enabled to realize compactness, a light weight and low price. And also a good optical performance being maintained, the few lens elements of the triplet lens further yielded a fair definition and optimum color balance due to a reduction in a ghost flare.

Now, let's check how Nikkor 10.5cm f/4 yields. Firstly, let's see the optical design sheets. It can be said that aberration characteristics of this lens was of a so-called WAKIMOTO balance, wherein a spherical aberration was a bit overly corrected whereby on stopping down at 1/2 of an aperture, an image would be sharply focused and lateral chromatic aberration was very few, and almost no distortion was present and further astigmatism was very small except for at certain edges of field whereby this lens was designed so that, on stopping down a little, highest definition would be given. If this 10.5cm f/4 is compared with 8.5cm f/1.5, you can understand what WAKIMOTO-san said that "This aberration balance (so-called WAKINOTO balance) is not necessarily optimum".

Nikon SP
Nikkor-T 10.5cm f/4
f/4 1/4 sec. RDP II
©2003/2004 SATO, Haruo

To be more specific, his saying meant that "Each lens has its own usage and the aberration balance of the lens has similarly its usage as the lens". As obvious from this aberration balance, it can be understood that 10.5cm f/4 was designed to ably meet a product concept placing greater emphasis on sharpness and ease-of-use than a lens speed.

Now, let's examine an end result picture based upon both of an end result picture taken at a long distance and design values. At maximum aperture, there is a residual flare a little bit, but on stopping down by a half or one-stop aperture, a high contrast and sharp definition are yielded. At f/5.6~f/11, almost no performance change by the aperture is present, whereas at f/16~f/22, an effect of diffraction reduces sharpness. Thus, optimum sharpness can be obtained at f/5.6~f/11.

Nikon SP
Nikkor-T 10.5cm f/4
f/5.6 plus a half stop 1/125 sec. RDP II
©2003/2004 SATO, Haruo

Next, let's check depiction characteristics with a sample picture. A sample 1 is taken in proximity to the closest point at f/4 (maximum aperture). It can be seen that a picture is soft a little bit, but a well-balanced contrast and moderate resolution are yielded, and an out-of-focus areas become picturesque more than expected. A sample 2 shows an example taken outdoors at f/5.6 plus a half stop, wherein softness in definition is almost gone and high contrast and sharp definitions are given. Further an image is produced very clearly and the lens tends to render hard a bit.

Anyway, it can be definitely said that this lens was the good buy lens sufficiently full of Nikkor quality far away from "low price and poor quality".

Training of newcomers to an optical design department at Nikon

Tonight, instead of our optical designers' chronicle, a training of newcomers at Nikon will be introduced hereunder. Our optical designing has a time-proven basic educational training system, in which an optical education starts with a ray tracing and newcomers study theory such as paraxial theory and aberration theory. And also, they are taught the basics of a lens design practice. When I was green then, I owed a lot of things to many mentors and senior members. Whoever may be a lecturer, however, every trainee was taught the rudimentary lessons of triplet designing almost 100% surely. Design specification was sure to begin with 105mm f/4. Once this design specification was complete, further widening of an angle of view and enlarging of a lens diameter were worked out and then a threshold of a lens type was determined. It is thought that probably as optical maturity of WAKIMOTO-designed 10.5cm f/4 was very high, the lens 10.5cm f/4 became a good example to them on a training course. In addition to the foregoing training, they further continue to receive optical design training in various lens types and also zoom lenses, wherein almost all the training was implemented by an old-line calculation means, not using a currently available convenient tool. On the course of this training, they came to realize thoroughly difficulty in correcting for distortion and overcoming lens type barriers. An optical design history at Nikon has been ceaselessly taken over like this. However convenient the tool is and however improved an automatic design is, a new invention is never created without overcoming the threshold or barrier of the tool. Whether an optical designer can come up with a fundamental, flexible and unique idea becomes an important key to enable to surpass these thresholds.

Note

This issue first appeared in "NIKKOR Club Quarterly" magazine; No. 187 (2003-12-31), published by the NIKKOR Club, and was revised for Nikon's webpage.
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