NIKKOR - The Thousand and One Nights No.77
The last lens for the Nikon S-series cameras,
a heaven-sent product for events
Nikkor-S 50mm f/1.4
Tale 77 takes us back to the story of lenses for the Nikon S-series cameras, a topic we haven't covered for a while. What sort of lens was the standard lens for the Nikon S3, the production of which was resumed in 1964? This f/1.4 lens was the only S mount lens for which the focal length was inscribed as 50mm rather than 5cm, expressed in millimeters. What secrets does the story of its development hold? What about the designer? In this tale, we'll look back at the memorable year of 1964 and uncover the secrets of the last S mount lens.
by Haruo Sato
I. A new standard lens for the S3 for which production was resumed
The year was 1964. In this memorable year, production of the Nikon S3 resumed with the switch to an all-black body. This black S3 would later come to have special meaning that made it a collector's item. So, just why did the rangefinder camera make a comeback at that particular time, when single-lens reflex cameras had already been available for quite some time? There is a theory that this comeback was inevitable given the needs of the press at the time. At that time, wide-angle lenses for SLR cameras were not as available or good as they are now. Therefore, photographers began to take another look at S-series cameras, which were compact and easy to use and for which there was a wide selection of wide-angle lenses. Even at that time, it was thought that rangefinder cameras were best suited to wide-angle photography and SLRs to telephoto photography. Then a great opportunity was presented. A new S-series camera that worked properly was needed. However, it seems that resuming production was not easy for Nikon at that time, even though only a few years had passed since the camera was last manufactured. What to do with the associated lenses in such a situation? A number of improvements to the 5cm f/1.4 lens for the SP-series cameras had been considered for some time. After much deliberation, it was decided that a new design would be adopted for the standard lens. One lens in particular stood out from the many design proposals presented, and the new 50mm f/1.4 was born.
II. Goodbye Sonnar, hello Gauss
As the number of Nikkor-S 50mm f/1.4 lenses manufactured was quite low and the lens was only sold for a short time, advertising brochures dedicated to the lens are few and far between. That is why the lens structure was only recently revealed. No one intended to keep it a secret so finding the cross-section for this lens was a complete coincidence. As a result, however, many rumors about the lens began to circulate. One of these that gained quite a bit of traction was that a cutting-edge Sonnar structure had been adopted. However, this lens was a genuine Gauss-type standard lens with an extravagant 7-element structure. Nippon Kogaku (the name under which Nikon was originally established) had researched the Sonnar type for many years and designed a variety of optical systems. The Sonnar type was the mainstream, particularly for S mount standard lenses. However, the last S mount standard lens was designed with an orthodox Gauss structure. Why was the Sonnar structure abandoned for the Gauss structure? There were several reasons. One was the introduction of new types of glass. Around this time, new types of lanthanum glass were developed and put into use. Lanthanum glass significantly increased the imaging performance of the Gauss structure. The use of lanthanum glass provided results that surpassed those possible with a Sonnar structure. Other companies were doing the same thing. Canon developed Gauss-type standard and mid-telephoto lenses early on. At the time, Nippon Kogaku produced a number of legendary Sonnar-type lenses. It seems that the switch to the Gauss structure for standard lenses was somewhat delayed. The only standard S mount lenses to utilize the Gauss structure were the 5cm f/1.1 and this 50mm f/1.4.
Then, why was there a switch from Sonnar to Gauss not only for standard lenses, but also lenses of a variety of focal lengths, during this time? There were two main reasons for this. The first is that the Gauss structure is better suited to larger diameters. The Sonnar structure is also suited to large diameters, but the maximum speed (brightness) of a true Sonnar structure that supports a 46° angle of view is around f/1.4. In addition, the Gauss structure is superior in terms of manufacturing ease. The second reason for the switch from Sonnar to Gauss was that the Sonnar structure exhibits greater short-range aberration fluctuation than does the Gauss structure. That is because the Sonnar structure has a telephoto-type power arrangement. After all, the Sonnar structure cannot surpass the symmetric Gauss structure in terms of short-range aberration fluctuation. On the other hand, two things are sacrificed by choosing the Gauss structure. One is size. The Gauss structure cannot compete with the Sonnar structure, which can make the system smaller with a shorter back focus. The second is that the Gauss structure is not very good at correcting sagittal coma. If you can look past these two issues, the Gauss structure is an excellent lens structure for easily achieving faster apertures. The choice made at that time was later proven to be correct in the SLR age. Thus, the Nikkor-S 50mm f/1.4 became the pioneer of standard Gauss lenses at Nikon.
III. Development history and the designer
Now let's take a look at the development history. Submission of the optical design report was recorded in November of 1962. It is unknown, however, when work on the design began. Prototype drawing was also issued in November 1962. I have heard that it was common at the time to submit the report at the same time as the drawings rather than to submit the report immediately after the design was completed. Therefore, the actual design was likely completed a little earlier. Mass-production drawing was issued in April of 1964. This means that full-scale mass production began in 1964. The optics were modified slightly after trial production before the lens was released. It is actually somewhat of a miracle that the lens was released in the memorable year of 1964.
The optics were designed by Yoshiyuki Shimizu, the originator of the Nikkor Auto who often appears in NIKKOR - The Thousand and One Nights. Shimizu's work greatly reflected the design technologies picked up from his mentor, the legendary designer Zenji Wakimoto. Shimizu designed a number of legendary lenses but it all began with the Nikkor-S 50mm f/1.4, his first lens. When I was new to the company, he often talked about his career that included many topics related to the development of this lens. I had an impression that Shimizu's career started from this lens. Shimizu originally worked polishing lenses. It seems that he was hand-picked by Wakimoto who must have seen Shimizu's potential to become a well-known lens designer. In fact, he had found a diamond in the rough. Shimizu received his introduction to optical design while studying optics at night school. Eventually, he completed his first lens design. It was the last S mount lens, the Nikkor-S 50mm f/1.4.
IV. Lens construction and characteristics
Now let's take a look at a cross-section of the Nikkor-S 50mm f/1.4 (Figure 1). Please forgive me if the following is quite technical. This lens is a typical 7-element Gauss-type lens. In order to maintain its f/.4 performance, the image-side convex lens in the 6-element construction was divided into two elements primarily for the good correction of spherical aberration and coma. Four of the seven elements were made of the new lanthanum glass. The introduction of cutting-edge glass materials at that time resulted in great design leaps. Extensive use of this glass made both spherical aberration correction and Petzval sum optimization possible. The lens doublet in front of the aperture is the so-called conventional achromatic lens (the refractive index of the concave lens is high), and the doublet behind the aperture is the new achromatic lens (the refractive index of the convex lens is high). This structure also helps to flatten the image plane by optimizing the Petzval sum while sufficiently correcting spherical aberration. This lens is the result of well thought-out use of glass materials, the optimal structure, and optimal bending. Superior performance and thorough consideration of rendering characteristics can be inferred with just a glance at this beautiful cross-section. It was Shimizu's first lens, but you can see that his optical design technique had already reached the level of a master. This lens hints at the dawn of the F mount era.
V. Design performance and evaluation
First let's look at design data. Before we consider aberration, the first thing we notice is that the maximum aperture design value is f/1.40. Aperture values are obtained by multiplying square root of two, so f/1.4 would actually be f/1.4141. Why did he intentionally design it to be faster (brighter)? The reason is that Shimizu was worried about the f-number issue exhibited by the Nikkor-S 5cm f/1.4 with its conventional Sonnar structure. I get a sense of Shimizu's spirit as a designer from this f-number.
Now let's look at aberration characteristics to get an idea of rendering characteristics. We'll start at infinity.
All aberrations are well corrected, but the most distinctive features are the lack of astigmatism all the way to the edges of the frame, and while there is slight curvature of field in the negative direction, the image plane is generally flat. Both meridional coma and sagittal coma are well suppressed from the center of the frame to the edges, and point-image reproduction is good. There is generally little chromatic aberration, so users can expect good images that exhibit clear and pleasing colors. There is little short-range aberration fluctuation, and the structure is clearly superior to that of the Sonnar structure in terms of sharpness. Furthermore, spherical aberration and curvature of field are under-corrected for pleasing background bokeh (blur characteristics) with shooting at finite distances. Measuring just -0.7% at infinity, the level of distortion exhibited is negligible. This design must have offered the best optical performance at the time. By the way, because I knew the aberration characteristics of this lens, I had decided on the revival of this lens when the production of the Nikon S3 was resumed for the second time. It was one of the most appealing S mount lenses at the time.
Next, let's look at point-image intensity distribution and spot diagrams. It is clear that, with the exception of the extreme edges, there is very little sagittal coma flare, a common weak point of the Gauss structure, along the focal plane. Point images are a little triangular in shape, but the lack of flare achieves generally pleasing results. In addition, extremely natural foreground and background bokeh is achieved with just a slight tendency toward double-line blur in the background.
Now let's look at MTF characteristics. First, MTF at 10 lines/mm is excellent at the best focus position with contrast reproduction of almost 80% near the center of the frame. The curve does not plummet from the middle of the frame to the edges, but rather maintains performance of 55-70% or better. Therefore, users of the lens can expect clear rendering performance. In addition, MTF at 30 lines/mm is excellent at the best focus position with contrast reproduction of almost 50% near the center of the frame. A gentle negative curvature of field is visible from the mid ranges to the edges of the frame, and the MTF peak moves in the negative direction. Even so, the meridional curve shows contrast reproduction of 30% to nearly 50%. The fact that the sagittal image plane exhibits a negative curve is rather favorable for point-image reproduction because it suppresses the occurrence of sagittal coma. These characteristics show sufficient levels of performance to support use with modern photographic systems.
VI. Low-pass filters and optical performance
The effects of low-pass filters and the optics associated with them on image quality have not generally been discussed much. Now is a good chance to consider this subject a little.
Interchangeable lenses for modern digital cameras vary from company to company, but all are designed with the assumption that they will be used with the low-pass filters built into basic models and the associated optics. Basically, optics are designed and their performance evaluated using systems that include low-pass filters. However, old lenses of the film age were designed for systems that did not have a low-pass filter or any other optics behind the lens. Therefore, some care is required when using an old lens with one of the latest digital cameras, as we did for this tale.
There are three things to keep in mind. They are exit pupil position, speed (brightness), and angle of view. That said, the exit pupil is not clearly indicated on the lens, so we have to guess. Lenses that users must be especially careful of are symmetrical wide-angle and ultra wide-angle lenses. And among these, the Biogon-type ultra wide-angle lenses require the most caution. When these symmetrical lenses are used with a common digital camera, a high degree of negative distortion occurs. Color fringing at the edges of the frame is also extreme. The degree to which these issues present increases as the thickness of the low-pass filter increases. In addition, the degree of aberration fluctuation varies depending upon the position of the pupil in relation to the image sensor.
Curvature of field also switches to a positive curvature. The larger the angle of view, the more attention to these characteristics must be paid. Fast (bright) lenses can also be problematic as spherical aberration switches to the positive direction as well.
Because of this, the optics that include the low-pass filter built into Z system cameras like the Z 6, Z 7, and Z 50 are designed with a minimalistic structure to be ultra slim so that they change aberration characteristics as little as possible when old NIKKOR lenses are used. That is another aspect of these cameras that makes them the best cameras to use with old lenses. The Nikon Z system plays a very active role in the writing of tales for NIKKOR - The Thousand and One Nights. I would like to test many more old lenses with these new cameras in the near future.
On a side note, the Z system was responsible for minimizing Nikkor-S 50mm f/1.4 aberration fluctuations. Further, as spherical aberration and curvature-of-field design values were originally slightly negative, it seems that this lens presented fewer problems than other old lenses might.
VII. Actual performance
Next let's look at results achieved with some actual images of distant scenes. I used the Nikon Z 7 with third-party mount adapters. I used a Nikon S-Leica L mount adapter a friend gave me, and was able to shoot by adding an ML ring and an M-Z mount adapter. The combination was a little expensive, but it effectively transformed the Z mount into the ultimate system. It will likely continue to play an active role in NIKKOR - The Thousand and One Nights tales.
I will explain performance at each aperture setting in detail. Evaluations are subjective, and based on individual preferences. Please keep in mind that my opinions on sample images and evaluations are for reference purposes only.
f/1.40 (maximum aperture)
The entire frame seems to be enveloped in a pleasing flare that is like a thin veil. However, resolution is still good. Sagittal coma flare is visible in frame peripheries. Flare gradually increases closer to the edges of the frame. I like the rendering characteristics, and think the gentle expression is well suited to portraiture.
By simply stopping down the aperture one stop, flare disappears and contrast increases from the center of the frame to the edges. Image quality, especially in terms of contrast, increases not only at the center of the frame, but also at the edges. Some flare remains only at the extreme edges of the frame.
Flare at the extreme edges of the frame disappears. Overall sharpness increases. Resolution is also better. This aperture setting achieves superior image quality throughout the frame.
Contrast increases further. Image quality is perfect! Stopping down the aperture to f/4 achieves sufficient level of the lens' capabilities. I would recommend this aperture setting for everyday use.
f/5.6, f/8, f/11
Excellent image quality is maintained consistently throughout the frame. Image quality does increase gradually as the aperture is stopped down to f/5.6, f/8, and f/11, but the differences are not great. Taking depth of field into consideration, f/8 to f/11 is recommended for landscapes.
While the image quality is consistent throughout the frame, there is a clear drop in contrast. This is likely the result of diffraction.
Aperture settings of f/1.4 to f/2.8 achieve the best results for portraits. f/8 to f/11 are likely best for landscapes. Anywhere from f/4 to f/8 is probably good for everyday snapshots.
VIII. Sample images
Now let's confirm these rendering characteristics with some sample photos.
These images have not been edited or enhanced so that you may judge the characteristics of this lens for yourself. For the most part, the images are portraits and landscape snapshots because I assume those to be the most common types of photos for which this lens would be used. I included backgrounds in the images again, and adjusted shooting distances slightly, to better show three-dimensional rendering characteristics.
Further, in addition to the usual shooting locations, I found a place with interesting lighting to shoot. I also chose clothing and background for making image comparison in terms of resolution easier.
Sample 1 was captured at the maximum aperture of f/1.4. The reproduction ratio was around -1/30 to -1/40x. The image is a little soft, but the normal print area exhibits sufficient sharpness. Bokeh characteristics are a little peculiar, but there are many relatively good areas that don't quite achieve double-line blur.
There is also no clear drop in sharpness in the intermediate and peripheral portions of the frame. Some color bleed, due to the effects of axial chromatic aberration, can be seen around bokeh but I think the level of correction provided is good for a lens of that era.
Overall, I think the rendering characteristics are well suited to portraits.
Samples 2 and 3 were also captured at the maximum aperture of f/1.4. These images were captured at a slightly shorter distance for a reproduction ratio of around -1/10 to -1/20x. Image quality is good with sufficient sharpness and detail, as well as a pleasing degree of contrast. Images are sharp but do not appear too harsh. It is clear that the lens is suited for use in most scenes. I chose a wall that extends from close to far distance with patterns and lighting that change continuously as the background for these images. While the background does not contain fine details, pleasing bokeh is rendered.
Sample 4 was also captured at the maximum aperture of f/1.4. The main subject is positioned at the center of the frame. I chose this composition to check the sharpness of the focal plane and the continuity of the bokeh. The reproduction ratio was likely around -1/30 to -1/40x. It is clear that the center of the frame is extremely sharp. Again, I chose a wall that extends from close to far distance with patterns and lighting that change continuously as the background for this image. That makes it easy to judge bokeh and three-dimensional rendering characteristics. I think the lens exhibits really good rendering characteristics.
Sample 5 is more of a close-up shot that was also captured at the maximum aperture of f/1.4. You can see that focus is sharp and clear, and bokeh is pleasing. These results simply would not be possible with a Sonnar structure. The small amount of short-range aberration fluctuation is the true advantage of a well-designed Gauss structure. I chose a place that offered a background with patterns and lighting that change continuously for these images as well. Both the foreground and background contain too many details and objects. That makes it easy to judge bokeh and three-dimensional rendering characteristics. I think the lens exhibits really good rendering characteristics with no double-line blur.
Sample 6 is a distant shot that was also captured at the maximum aperture of f/1.4. Focus is sharp and clear. Anyone can see that this lens can be used without concern from maximum aperture.
I've only included images captured at maximum aperture in this tale but I shot certain sample images at each aperture setting. The aperture setting of f/5.6 to f/8 at which landscapes are often captured presented no problems at all. You can see that this lens is almost an all-purpose standard lens. I continue to be impressed by the fact that this almost perfect NIKKOR lens was the first that Shimizu designed. He was a born master. His talent is truly incomparable.
IX. A third round of S3 production
There was a lot of talk around the company. People were saying that we would finally resume production of the Nikon S rangefinder cameras! At that time, I was designing interchangeable F mount lenses. When I asked my superior, he told me that it was still top secret, but that we would resume production of the S3 first. He said he had already asked Teruyoshi Tsunashima to think about lenses for the camera. I ran to Tsunashima! He told me that he was redesigning the Sonnar structure for the 5cm f/1.4. I then consulted Tsunashima and his boss at the time, Takahashi. I told them that there were plenty of 5cm f/1.4 Sonnars on the street, and it was a phantom standard lens with a Gauss structure—the last Nikkor 50mm f/1.4 for the S mount—that our customers wanted, and asked them to find a way to resume production of that lens that would offer exactly the same level of aberration correction using modern (at the time) glass materials. Both were convinced, and decided that the development of the new lens would be assigned to me. I was pleased, but only for a short time. In accordance with company policy, this project was to be handled by a subsidiary. Sendai Nikon was in charge of the camera, and Tochigi Nikon of lens design. Fujita, the most experienced lens designer at Tochigi Nikon was the first choice for the project. He had studied design in the optics department at Nikon headquarters ever since he joined the company many years prior. I knew him well. He was an old friend. I asked Fujita for the actual design, and I was put in charge of confirming aberration correction balance and rendering characteristics. The latest glass materials were used and aberration correction perfectly imitated that of the original. The latest multi-layer coating was, however, adopted. This change was made because I don't think that ghost and flare should be considered positive characteristics of a lens. I thought we had reproduced the original lens perfectly.
Then we got a phone call. It was Fujita from Tochigi Nikon. He said that if design values and drawings were followed, then the lens would not focus at short distances, and asked what he should do. We considered the matter in depth, and realized that the problem could be solved by adjusting the amount of extension needed to focus. The focal length should be changed from 51.6 mm to about 52 mm to adjust the amount of extension. Changing the focal length required a whole new design. I felt a chill come over me. However, Fujita said that the focal length could be changed to 52 mm with no change in aberration by changing the radius of curvature of the last lens element very slightly. I remembered a story I'd heard from Shimizu years before. A long time ago, he'd been in a hurry with his first job (optical design). A lens he'd designed with a focal length of 51.6 mm would not focus with the S-type rangefinder, so he adjusted the radius of curvature of the last lens element to 52 mm during trial production. I was going down that same path. It was ironic that I'd reproduced every last detail. The inner flange system on cameras like the S-series models has an extender function on the camera. The amount of extension is determined by the focal length with lenses for which a mechanism that the entire optical system extends. A Sonnar-type 5cm f/1.4 should have a focal length of 51.6 mm. Then why did the Gauss-type 50mm f/1.4 have to have a 52 mm focal length? That is the result of residual short-range aberrations. The Sonnar structure exhibits greater short-range aberration fluctuation than does the Gauss structure. As the rangefinder was adjusted for the Sonnar structure, it is thought that it was over-corrected for the Gauss structure, which exhibits less short-range aberration fluctuation. The final adjustment for eliminating this gap was the slight extension of the focal length. Thus, we resumed the production of the S3, once resumed with an all-black body, again. At that time, I invited an important superior who was involved in the design and manufacture of the original lens to the factory, so that he could explain the technology to the young engineers. This was extremely beneficial for Nikon. We were finally about to resume production of the ultimate rangefinder camera, the Nikon SP. Naturally selection and design of the lens was the job of Fujita from Tochigi Nikon and myself. The next lens selected for resumed production was Hideo Azuma's famous 3.5cm f/1.8.