NIKKOR - The Thousand and One Nights No.10

AI Nikkor ED 180mm F2.8S

As I informed in the last part of Tale Eight, I discuss about one of typical telephoto lenses "AI Nikkor 180mm f/2.8 ED" this time.

by Kouichi Ohshita

I. Affordable ED lens

The origin of the lens having specifications of 180mm f/2.8 goes back to "NIKKOR Auto 180mm f/2.8" that was released to the press only for the Sapporo Pre-Olympics in 1970 and released to general users in the next year 1971.

The focal length of 180mm further goes back to "NIKKOR-H 18cm f/2.5" released for Nikon S in 1953 and this lens has a preset stop and was too large and heavy for hand-held shooting.
This "NIKKOR Auto", therefore, was designed as a bit compact lens that has the attachment size of 72mm diameter by making the f-number a little slower to f/2.8 and adopting the optical system of Ernostar type that enables to reduce the overall length of the lens.

The design of optics was made by Mr. MATSUI, Sei. He worked in very wide area such as interchangeable lenses for Nikon F, finder optics of Nikon F2 and lenses for NIKONOS.
This "NIKKOR Auto 180mm f/2.8" was his first work of interchangeable lenses for Nikon F.
This lens was a state-of-the-art compact large-aperture telephoto for that time and conveniently used for the indoor sports and the stage photography.

This "NIKKOR Auto 180mm f/2.8" was applied with the multi-layer coating later in 1976 and was modified to "AI Nikkor 180mm f/2.8" in the next year 1977 and it still enjoys wide popularity as a high-performance large-aperture telephoto lens.

The "AI Nikkor 180mm f/2.8 ED" introduced this time was released in 1981 as the successor of "AI Nikkor 180mm f/2.8".
The optical design was made by Mr. MATSUI again.

Mr. MATSUI's answer to the challenge of improving the performance of NIKKOR Auto without changing its size was the adoption of the new lens type with five (5)-group, five (5)-element structure and ED (Extra-low Dispersion) glass.

The release of this lens which attained higher performance by adopting ED glass was, in a sense, an epock-making event. At that time, the lens using ED glass means an expensive, heavy, high-speed lens such as 300mm f/2.8 that general photo enthusiasts cannot be ready to purchase. However, the ED lens was made more accessible by the appearance of this lens.

I who was a student at the time when this lens was released, was looking enviously at the lens barrel proudly putting on a gold ring every time when I went to Nikon's service station.
Seeming obtainable but being not obtainable, this ED lens that can take a sharp enlarged photograph of nebula and cluster of stars was a lens longed for by me since I was mainly taking astronomical photographs at that time.
And it was the first lens I bought after joining the company and it is a lens full of memories.

II. Lens performance

This is a typical telephoto type lens with 5-group 5-element structure as shown in the cross-sectional view in Fig. 1.

Telephoto type means a lens structure of convex front group and concave rear group. In case of this lens, the front group consists of three elements, convex-concave-convex and the rear group consists of two elements, concave-convex, and ED glass is used for the top lens and the glass material capable of well correcting chromatic aberration when combined with ED glass is used for the second concave lens.

Thus the lateral chromatic aberration which is always the problem with the telephoto lens is excellently corrected.
The feature of the telephoto type is to enable to make the overall length of the lens shorter than its focal length owing to the function of the rear-group concave lens. On the other hand, it has a drawback of generating a pincushion type distortion.
In this lens, therefore, the structure of the rear group is made of two elements, concave and convex and this pincushion type distortion is cancelled out by the function of the last convex lens.

Further, this telephoto type has another feature of capability of correction aberrations by composing each lens with a thin lens, and it may be another feature of this lens that its size and weight is reduced in comparison to the former "NIKKOR Auto 180mm f/2.8".
The effort paid by the designer of the lens barrel must have contributed very much to the down-sizing of the lens.

The lens is flawless with very well corrected aberrations including chromatic aberration and coma aberration. It is a high-performance lens that can be used even at the full open aperture.

Lens performance

Let's take a look at how this lens performs.

Though it is my personal impression, the word "neat" would exactly fit for expressing the performance of this lens. It catches the subject as it is, not elimination any detailed part and without flaws, whatever the subject is.

Example 1. displays ume (Japanese apricot) blossoms just began to open in early spring. An ume (Japanese plum) tree is a difficult subject that requires clever management of the background since its shape is twisting and blossoms bloom directly on branches. This lens is the most suitable for taking this kind of tree since it has both a large aperture of f/2.8 and a focal length of 180mm that has enough telephoto power. Large and beautiful defocus images emphasize the subject with leaving out the background and foreground which tend to be mixed up in disorder.
The distinctive feature of this lens is the beautiful defocused images in addition to the sharp focus.

Example 2. is a photograph of stars, the central part of Orion. A star is a point-source light and is a most difficult subject since the slightest coma and chromatic aberration generate flares around the light source. But this lens has very high performance so that it can be used even the full open aperture with this type of difficult subject. As blue flares around the bright stars due to chromatic aberration are hardly found, uniform and sharp image of stars may be obtained even to the periphery of the frame.

When stopped down one or two stops, the image becomes more uniform. This example was taken at the aperture stopped down one stop to obtain more uniform image over the entire frame. I have been using this lens for a long time but I have no memory of finding noticeable ghost images. It is another appeal of this lens that it can be used in the back-lighted situation with a sense of security.

Difference in lens performance of successive generations of 180mm f/2.8 lenses

Most of you are interested in the difference in lens performance of successive generations of 180mm f/2.8, aren't you ? Though I haven't compared them very much, I want to tell a little of my personal impression on it.

I have an impression that the sharpness "NIKKOR Auto" is slightly less than that of its successors, two models of ED lenses. It gives a soft rendition, in a way that the profile of the subject is a little shade off (sfumato), influenced by residual chromatic aberration and coma. However, this slight flares may sometimes give a wet and quiet mood depending on the type of the subject. It reminds us that the sharp lens with less aberrations is not always the best.

On the other hand, two ED lenses make the extremely uniform and sharp image so that the deterioration of the image quality in the periphery of the frame is hardly perceptible.
"AI AF NIKKOR ED", in particular, gives uniform and sharp image from infinity to the closest distance due to Nikon's original IF system, as is expected of the latest design.
"AI NIKKOR ED" gives excellent performance from infinity to medium distances, especially the clearness of color is superb. The defocus characteristics are very good with all three lenses but the details of characteristics are delicately different.

"NIKKOR Auto" has a character of coloring the fringe of rear defocus in yellowish green and front defocus in reddish purple by influence of the residual chromatic aberration. The residual chromatic aberration influences not only to the focused plane but also to the front and rear defocused images.

On the other hand, the coloring of the fringe of defocus with "AI NIKKOR ED" is very little and the defocused images appear smooth.
This is similar to "AI AF NIKKOR ED" as well, images taken are so alike that sometimes we cannot know the one from the other depending on the shooting condition.

If I am pressed to mention the difference, with "AI NIKKOR ED", the defocus linked from the focused plane to the front defocus appears hard, and with "AI AF NIKKOR ED" the rear defocus just behind the focused plane appears hard.

Of course, the difference in lens performance is profound and you might have quite another impression depending on the type of the subject and the shooting conditions. If you have two or more lenses, please compare and check up the difference with your eyes.
It may be one of the pleasures of photography to find the features of lenses in possession and to use a lens properly depending on the subject and the shooting condition.