NIKKOR - The Thousand and One Nights No.62
Zoom-Nikkor Auto 50-300mm f/4.5
As introduced with Tale 58, one of the major keys in the development of zoom lenses was expansion of the zoom ratio. The passion of lens designers to create all-purpose lenses knows no boundaries. It is what led to lenses like the AF-S DX NIKKOR 18-300mm f/3.5-5.6G ED VR and AF-S NIKKOR 28-300mm f/3.5-5.6G ED VR sold today with zoom ratios exceeding 10x. In this Tale, we will look at the Zoom-Nikkor Auto 50-300mm f/4.5, which represents the origins of today's high-power zoom lenses. Just how did this lens, which can be called the first high-power zoom lens for still cameras, come to be?
by Kouichi Ohshita
I. Nikon Zoom 8
Let's begin by looking at what was happening around the time this lens was released.
This 50-300mm lens was released in 1967, the fourth to follow the Zoom-Nikkor Auto 43-86mm f/3.5 (released in 1963) mentioned in Tale 4 (fifth if we count the ephemeral 35-80mm f/2.8-4, which never went into mass production). At that time, the only wide-angle lenses for the F mount were a 35mm f/2.8, a 35mm f/2, and a 28mm f/3.5 if we exclude the 21mm f/4 that could be mounted with the mirror raised and fisheye lenses. A 24mm f/2.8 lens was released roughly six months after this lens. How was a lens that supported 6x zoom ever achieved at this, the dawn of the era of SLRs and interchangeable lenses? All early Zoom-Nikkor lenses, beginning with the 43-86mm, were designed by Mr. Takashi Higuchi. Mr. Higuchi was researching zoom lens design at that time, and there even came a time when Mr. Higuchi was automatically associated with all zoom work at Nikon. This was around 1962, a little while before this lens was released.
At that time, Nikon (Nippon Kogaku) manufactured and sold 8mm movie cameras alongside their 35mm format cameras like the Nikon F. Demand for zoom capabilities of 8mm movie cameras, like we see with modern video cameras, was much greater than it was for 35mm still cameras. The Nikon Zoom 8 was released in 1962 in response to this demand. The Zoom 8 looked like a small box with a built-in 8-32mm (4x) zoom lens. Both its design and performance were very well received. Naturally, the lens for thismovie camera was designed by Mr. Higuchi. When Mr. Higuchi finished designing the 43-86mm lens that he researched at the same time as he was researching and designing the lens for the 8mm movie camera, he immediately began improving the design of the Zoom 8 lens.
Shortly afterward, Mr. Higuchi had designed and begun trial production of a completely new lens with a greatly expanded zoom ratio for the 8mm format. After a number of design modifications, this lens was adopted for the Nikon Super Zoom 8 (released in 1966). The data upon which Super Zoom 8 lens was designed formed the basis of Mr. Higuchi's idea to design a high-power zoom lens for the 35mm format.
He was certain that the same type of zoom construction could be used to achieve the high-power zoom lens of his dreams for the 35mm format. That is how Mr. Higuchi came to be involved in designing the 50-300mm lens while working on lenses for 8mm movie cameras.
However, designing zoom lenses for the 35mm format is not easy. While it is true that the 35mm format has the advantage of supporting designs with slower (darker) apertures than is possible with lenses for the 8mm format, 35mm frame size is six times larger than Super 8 frame size. This does not just mean that images are magnified; aberration is also magnified far too much for practical use. When Mr. Higuchi's first lens went into trial production, he found that its basic performance was insufficient. It had to be redesigned. The level of compensation for chromatic aberration was especially disappointing. Even Mr. Higuchi, who had by that point designed four zoom lenses for the 35mm format, had a difficult time designing the first high-power zoom lens for the 35mm format. He then modified lens construction greatly, and went through redesigning, trial production, and evaluation of the lens almost every year. He was finally satisfied with the performance exhibited by the third version of the lens. This was roughly three years after he finished designing the lens for 8mm movie cameras that inspired him to design a high-power zoom lens for the 35mm format.
III. Lens construction
Let's take a look at construction of the completed lens.
Fig. 1 at right is a cross section of the Zoom-Nikkor Auto 50-300mm f/4.5. The photo below that shows the lens zoomed out to the 50mm position, and the bottom photo shows it zoomed in to 300mm.
This lens has a four-group zoom lens construction.
The first, third, and fourth convex groups have positive refracting power while the second concave group has negative refracting power. Even today, high-power zoom lenses using a four-group zoom structure are made, but this lens utilized unique movement not found with modern lenses.
When zoomed in, the first and third groups were moved as one in the direction of the object (photographic subject) while the second group was moved by a cam toward the focal plane. The fourth group was not moved. With modern four-group zoom lenses, all groups move and the amount of movement varies with each group, but this lens was constructed so that virtually only two groups move—one (first and third together) toward the subject and one (second), which is the only group moved via a cam, toward the focal plane. As I also explained with regard to the 43-86mm lens introduced in Tale 4, considering the level of precision available at the time, Mr. Higuchi likely wanted to minimize the number of moving groups.
In addition, the amount of movement exhibited by each group was minimized to achieve the desired zoom ratio efficiently, and aberration was also efficiently compensated. The variable power exhibited by this lens is due solely to movement of the first three groups. Positioning the fourth group closest to the focal plane in the structure means that the first three groups can be used for the sole purpose of controlling changes in aberration that occur with zooming. The fourth and last group adjusts the aberration that couldn't be compensated by the first three groups for better overall aberration balance, increasing performance throughout the entire zoom range. Another role played by the fourth group was to function as a teleconverter, extending the focal length. The existence of this fourth group minimized the amount of movement required by the other three groups, which in turn enabled an overall shorter and smaller lens.
I think this four-group zoom structure was just what Mr. Higuchi was looking for when his idea to design a high-power zoom lens for the 35mm format struck. As the first group moves toward the photographic subject when the lens is zoomed in with this structure (a structure with which the total length is short at wide-angle positions), the lens element at the extreme front of the lens could be smaller. Further, the addition of a fourth group meant that the changes in aberration that occur with zooming could be controlled even when the first and third groups were moved as one, and the fourth group acting as a teleconverter allowed for a relatively small overall size, even with a greater zoom ratio. I think it is safe to say that in achieving this four-group structure, Mr. Higuchi killed about four birds with one stone. It is also how he was able to complete the high-power zoom lens of his dreams.
IV. Lens rendering
As always, let's take a look at the rendering characteristics of this lens with optical simulations and actual photos.
First, the results of simulations were surprising in that despite being a 6x zoom lens, we found that changes in aberration that occur as the zoom ratio and shooting distance changes are controlled far better than they were with the 43-86mm lens. For example, the distortion that is almost guaranteed with this sort of zoom lens is barrel shaped at 50mm and pincushion shaped at 300mm. However, the degree of distortion at both ends is less than with the 43-86mm lens, and is compensated to about the same degree as you find with zoom lenses sold today. What's more, changes in the level of performance exhibited as shooting distance changes with each focal length have been minimized, giving us the sense that design technologies had progressed.
Next let's look at changes in imaging performance at various focal lengths.
At the 50mm focal length, barrel distortion is slightly noticeable. Compensation for spherical aberration and axial chromatic aberration is good, and images that are sharp at the center of the frame from maximum aperture are achieved. However, lateral chromatic aberration remains at the edges of the frame, and the effects of outer coma make for soft rendering. Sample 1 was captured at a focal length of 50mm and aperture setting of f/11, which eliminates the effects of coma for a sharp and clear image. On the other hand, lateral chromatic aberration is not eliminated by stopping down the aperture, and color fringing is slightly noticeable in this sample image. When the lens is used with a Nikon digital camera, lateral chromatic aberration is automatically compensated to the point that it is not noticeable with normal use. It is noticeable in the sample image because lateral chromatic aberration compensation was disabled with processing of the RAW image.
This lens offers the same focal length as the AI 50mm f/1.8 covered in Tale 60, but at 2.3 kg, it is not a lens that is easily carried for simple hand-held snapshots. It is a lens meant to be used with a tripod.
Sample 2 was captured at the 105mm focal length and maximum aperture.
If we zoom in to the 105mm position, distortion changes somewhat to pincushion type, and lateral chromatic aberration and outer coma are eliminated for the best rendering in the zoom range.
Background blur tends to be double-line blur, but I think that even with comparison to the latest lenses, the rendering characteristics exhibited by this lens at this focal length can be considered quite good.
Sample 3 was captured at the 135mm focal length and maximum aperture. Zooming in further to the 135mm focal length, there is still little lateral chromatic aberration, but coma tends to shift to inner coma.
As a result, the edges of the frame are a little more affected by flare than at the 105mm position. This coma can be markedly improved by stopping down the aperture to f/8. The image does exhibit pincushion distortion, but there are probably few scenes with which it would be noticeable. Blur is characterized by a unique shape that, while not exactly beautiful, I find attractive because it seems a little softer than the blur exhibited at the 105mm position.
At 200mm, the axial chromatic aberration typical of telephoto lenses begins to be significant, with the most naturally exhibited at the 300mm position. However, at 300mm there tends to be no coma and imagining performance of individual colors improves. Samples 4 and 5 were both captured at the 300mm position. Sample 4 was captured at maximum aperture, and Sample 5 was captured at f/8. You can see that in Sample 4 captured at maximum aperture, portions that are in focus exhibit some flare, and the light blue fringe at the edges of the flower petals is noticeable in portions that are just slightly out of focus.
These issues are nearly eliminated, and sharp and clear rendering is achieved by stopping down the aperture to f/8 as in Sample 5.
As a large lens, there is a relatively large amount of peripheral illumination, and I think that there are probably few scenes with which peripheral illumination falloff would be noticeable, even with shooting at maximum aperture. However, it is a little concerning at 50mm and 300mm with a subject at the minimum focus distance as with Sample 4. As Sample 5 shows, however, such concerns can be mitigated by stopping down the aperture to around f/8.
This Zoom-Nikkor Auto 50-300mm f/4.5 was released in 1967, one year after the Nikon Super Zoom 8, which can be considered an elder twin. While this was a large and expensive lens that was not a tremendous hit, it was widely used to capture sports and nature photos. The new Zoom-Nikkor 50-300mm f/4.5 with a new exterior and for which a multi-layer coating was adopted was released in 1975, and a successor model, the AI Zoom-Nikkor 50-300mm f/4.5 was released two years later, in 1977.
In fact, since the AI Zoom-Nikkor 50-300mm f/4.5 ED, which can be called an improved version of the AI Zoom-Nikkor 50-300mm f/4.5, was also released in 1977, it seems there was no need to continue selling this lens. However, I suppose that the fact that the AI Zoom-Nikkor 50-300mm f/4.5 was sold alongside its ED version can be seen as evidence of the popularity and merits of this lens. Adoption of an ED lens element with the 50-300mm ED overcame the chromatic aberration weakness exhibited by the original Zoom-Nikkor Auto 50-300mm f/4.5. 45mm shorter, it was a high-performance lens that contributed to the expansion of the world of high-power zoom. I would love to talk about this 50-300mm ED lens should the opportunity ever arise.