NIKKOR - The Thousand and One Nights No.80
The E-series telephoto lens known for its light weight
Nikon Series E 100mm f/2.8
Following Tale 76, we'll pick up another E-series lens, the telephoto Nikon Series E 100mm f/2.8, which was sold in Japan as well as abroad.
by Kouichi Ohshita
The first lens in the Nikon E series
I talked about how development of the Nikon EM and Series E lenses released in 1979 in the U.S. and in 1980 in Japan came about in Tale 76. Please refer to that tale for the details. The Nikon Series E 100mm f/2.8 was the first E-series lens and, along with the Nikon Series E 35mm f/2.5, may be considered one of the best representatives of the Series E lenses. The Nikon Series E 75-150mm f/3.5 introduced with Tale 42, and the Nikon Series E 135mm f/2.8 introduced with Tale 76, were also E-series lenses that were the result of a variety of cost-reduction measures, but the long focal length of the zoom lens, and the use of metal components on lens exteriors made them quite large and heavy. With this lens, however, engineered plastics were used for a number of external and internal components, making it surprisingly lightweight. The AI Nikkor 105mm f/2.5S with its short focal length was available, but with a weight about half that of the AI lens, the Series E 100mm f/2.8 had the perfect compact size and light weight for the little Nikon EM.
The Nikon Series E 100mm f/2.8
The 100mm f/2.8 E-series lens was designed by Sei Matsui. It is unclear when design work began, but it seems to have been sometime in early 1977, around spring. The design was completed around the summer of the same year, and a prototype was made. Unfortunately, the prototype did not perform as expected, and it was decided that improvements to the design would be made. There is a report that provides data from the original prototype, and when the performance indicated by that data is reproduced, we see that a large amount of purple axial chromatic aberration remains, even with compensation. In addition, as performance fluctuated greatly depending upon the shooting distance, and the lens was designed to offer the best performance with shooting at close distances, rendering with longer distances, and especially at infinity, appears to have been influenced by flare. It is for these two reasons that I believe the lens did not offer the expected level of performance. Matsui worked on an improved design that was completed in the early summer of 1978. The final Nikon Series E 100mm f/2.8, a cross section of which is shown below, was then achieved based on the new prototype.
The Ernostar structure of four elements in four groups introduced in Tale 76 was also adopted for this lens. Considering the time these products were developed, it may be more accurate to say that this Nikon Series E 100mm f/2.8 served as the model for the Nikon Series E 135mm f/2.8 introduced in Tale 76.
One primary characteristic of the Ernostar structure is a convex-concave-convex triplet that includes a meniscus-shaped convex lens element between the convex and concave elements at the front of the lens, which provides good correction for spherical aberration and coma, even when fast (bright) apertures are used. There is, however, one drawback that aberration varies greatly with shooting distance. Despite the struggle for achieving balanced performance with development, favorable performance with balanced design was achieved with this lens, since the first prototype, which enabled the degree of variation dependent upon shooting distance to be small as well as maintained the optimal performance at shooting distances of infinity to close-up (bust shot). While this very asymmetrical optical system gives rise to concern for pincushion distortion, it is not noticeable even with capture of straight lines, such as those in buildings, as that form of distortion was suppressed to about 1%.
As always, let's take a look at the rendering characteristics of this lens with actual images. The sample images for this tale were captured using the Z 6 full-frame mirrorless camera and FTZ mount adapter. Series E lenses are basically AI-S manual focusing lenses for the Nikon F mount. When mounted to a mirrorless camera using the FTZ mount adapter, aperture-priority AE shooting with actual aperture metering is possible. However, as lens information is not transmitted to the camera, focal length and aperture information must be registered with the camera. Registering this information enables recording of focal length information in image Exif data as well proper in-camera VR operation.
Sample image 1 is a photo of rapeseed plants in bloom captured at maximum aperture at a distance of 2 to 3 m. This sort of photo, which utilizes both foreground and background bokeh, is typical of the sort of image for which photographers often use 100mm-class telephoto lenses. In-focus blossoms are sharp, and the large foreground and background bokeh is smoothly blurred, as would be expected. However, with close inspection, we can see that the edges of blossoms in the foreground are slightly reddish, making them stand out. This is the effect of the remaining axial chromatic aberration and under-corrected spherical aberration.
Sample image 2 is a photo of cherry blossoms captured at f/4 at a distance of approximately 5 m. This sample image was captured to achieve only background bokeh with virtually no foreground blur. However, by stopping down the aperture one stop, the coloring around the edges of blur exhibited in Sample image 1 is almost completely eliminated. Blur that takes the heptagonal shape of the seven-blade aperture visible in extremely bright portions may be a matter of personal preference.
Sample image 3 is a distance landscape photo captured at f/8. The lens produces a uniform image from the center of the frame to the edges at a distance of about 3 m from infinity. However, as a small amount of axial chromatic aberration and spherical aberration remains when maximum aperture is used, it is better to stop the aperture down two stops (to f/5.6) to achieve a sharper image. In addition, there is some peripheral illumination falloff at maximum aperture, so stopping down to f/4 or f/5.6 makes the amount of light uniform throughout the frame. With this sample image, I stopped down to f/8 to achieve a deeper depth of field from the closer blossoms to those farther back.
Sample image 4 is a photo of semi-double flowered cherry blossoms captured at a close distance of 1 m. As has been mentioned many times in NIKKOR The Thousand and One Nights tales, this lens has also adopted the Ernostar structure that exhibits relatively large variations in aberration dependent upon shooting distance. At close distances, spherical aberration is not sufficiently corrected, and the image plane exhibits a negative curve and outer coma is visible at the edges of the frame. This causes images captured at short distances to appear to be influenced by flare, especially at image peripheries. Therefore, I stopped down the aperture to f/4 for this sample image, but flare is still visible in the rendering of cherry blossoms at the edges of the frame. To reduce this flare, the aperture should be stopped down to f/5.6-f/8, but the foreground and background will be less blurred. Therefore, the aperture setting should be selected based upon shooting intent. Personally, I like a little flare when photographing flowers. It expresses light and the freshness of blossoms.
Sample image 5 is a photo of tulips also captured at a short distance of 1 to 1.5 m. This image was taken at f/2.8 (maximum aperture), so a little flare can be seen in the rendering of petals at the center of the frame. In addition, if you look at the flowers on both the left and right sides of the frame, it may seem that they are slightly closer to the camera than are the flowers at the center of the frame on which focus is acquired. This is a characteristic of the lens, and is the result of curving of the image plane in the negative direction with shooting at close distances. This characteristic can be annoying when photographing flat scenes or subjects, but not so much for three-dimensional scenes and subjects like those in this sample image.
My encounter with the Series E 100mm f/2.8
I was first introduced to this lens about 40 years ago by a junior member of the university's astronomy club who purchased it along with a Nikon EM. I was surprised at the small size and weight of both the EM and this lens, but I was also impressed by the quality of images it captured.
After starting work at Nikon (Nippon Kogaku K. K. at that time), I was looking to purchase a medium-telephoto (around 100mm) lens. I borrowed and tried a number of lenses we had on hand, and confirmed their performance with simulations as work allowed. Haruo Sato, a friend from the time I joined Nikon, recommended the Nikkor 105mm f/2.5, which he had been using for some time. Rather than getting the same lens he had, I preferred to enjoy a different lens so I purchased the Series E 100mm f/2.8. The driving forces behind my decision were the results of simulations comparing the Series E lens with the AI 105mm lens and the feel of actually using it. Performance, including bokeh from infinity to middle ranges, is actually very similar to that of the AI 105mm. Naturally, evaluation of aberration levels and characteristics at a desk does not tell the whole story of lens performance. Considering all aspects of lens construction, including the coatings used, the AI 105mm f/2.5 achieves deeper colors and more beautiful rendering under harsh shooting conditions, including backlighting. That said, I was attracted by the ability to correct aberrations, as well as the pride in the Series E lenses that offered the uncompromising optical performance even with popular-class models.
Once I had purchased the Series E 100mm f/2.8, it became my favorite lens for travel photography and portraits. However, I did part with it when I purchased a Micro lens. Ultimately, the Series E lens was difficult to use for scenes like that in Sample image 4 because the minimum focusing distance is 1 m. With a Micro lens offering the same focal length, I hastily decided I didn't need the Series E lens. Once I no longer had it, however, I missed the compact and lightweight feel of the lens, and purchased another that a camera store had been unable to sell a few years later. Now I've parted with the lens again, but I'm secretly hoping for the chance to buy a used one that I can keep on hand. The appeal of this lens that makes users miss it, no matter how many times they let it go, is its compact and lightweight size, as well as it's faithful rendering. This cute little lens can easily be carried in a small side pocket, even when users want to keep their belongings at a minimum while traveling.