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Optical Design value Analysis - NIKON AiAF NIKKOR 28mm F2.8 D [No.029]

This is a performance analysis and review article of the NIKON AiAF NIKKOR 28mm F2.8 D

You hardly understand the specific differences in how the lenses work and how their performance differs from each other, do you?

Even if you look it up in magazines or on the Internet, all you will find are similar "word-of-mouth recommendations" and articles like that.

In this blog, while researching the history of lenses and their historical background, we estimate lens design performance based on patent information and actual shooting examples, and analyze lens performance in detail from a technical viewpoint through simulations.

Professional lens designer Jin Takayama will carefully unravel optical characteristics such as optical path diagrams and aberrations, which are generally not visible, and explain the taste and descriptive performance of lenses in a deep and gentle manner.

Now, please enjoy the special information that you can read only on this blog in the world.

Overview

At the time of writing (2020), the NIKKOR 28mm F2.8 seems to have already been discontinued, but it is still available in stores and can be purchased new.

The 28mm focal length itself is an unfortunate focal length that is in danger of extinction, but Nikon's 28mm F2.8 is also a lens that is practically certain to become extinct as there is no successor model.

First, let's look at the lineage of NIKON's traditional 28mm F2.8 lenses side by side as follows: The first NIKKOR 28mm in the 1960s was an F3.5 lens, but the history of the F2.8 lens began with the New NIKKOR 28mm in 1974.

  • New Nikkor 28mm F2.8 (1974)7/7
  • Ai Nikkor 28mm F2.8 (1977)7/7
  • Ai Nikkor 28mm F2.8S(1981)8/8
  • Ai AF Nikkor 28mm F2.8S(1991)5/5
  • Ai AF Nikkor 28mm F2.8D(1994)6/6

groups/elements

Although it has a long history, the optical system seems to have been changed from time to time, which is surprising when you look at the changes in the number of lens elements.

The lens we will focus on here is the Ai AF Nikkor 28mm F2.8D, which was released in 1994 and was the final product in the series. I would like to analyze and compare all of them in the future.

The appearance is similar to the NIKKOR 35mm F2.0D and 50mm F1.8D of the same series, and although it has a strong plastic look, it has a nice retro design with an 80's feel.

Private Memoirs

The 28mm focal length was often used in compact cameras in the past because it was "close to the natural viewing angle when viewed with both eyes," and the 50mm to 28mm range was also sometimes treated as a standard lens.

If you were a camera hobbyist, I think it was one of the lenses you were sure to own in one form or another.

It was also one of the first lenses that led many people into the lens swamp, as in, "I started photography with the 50mm lens, then moved on to the 28mm lens, then became interested in the 35mm lens…" I think it was one of the first lenses that led many people into the swamp.

As time went by and the zoom era was in full swing, the popularity of the 28mm lens plummeted as a single focal length because it existed within the range of standard zoom lenses.

Also, wide-angle lenses do not produce much shake, so even if the f/number is brightened, it is not very gratifying, and there is little difference in the image quality such as bokeh, etc. It was difficult to create a distinctive feature, and it finally became an existence in danger of extinction.

Whenever I see a 24mm lens at the wide-angle end of a standard zoom lens these days, I think, "Why not just use a 28mm lens?

Document Survey

Although the lens is somewhat old, it was sold until recently, so it was easy to find the patent information on Nikon's official website, which is JP 6-300965.

Since Example 2 seems to be close to the product in terms of appearance, we will reproduce it below using this as the design value.

Notes!

The following design values have been selected and reproduced from the appropriate patent literature and do not correspond to the actual product. Naturally, the data is not guaranteed, and I am not responsible for any accidents or damages that may occur by using this data.

Analysis of Design Values

Optical Path Diagram

Above is the optical path diagram of the NIKKOR 28 F2.8D.

It is a retro-type wide-angle lens with 6 elements in 6 groups and a strong concave lens on the subject side. Since aspherical lenses are not used, a convex lens is placed on the subject side to compensate for distortion and curvature of the image plane.

The thick convex lens is located around the aperture, which is a common configuration for lenses of this era, and the thickness of the glass is used to correct spherical aberration with a small number of lenses.

This is not often seen in today's lenses, which have more lenses or use aspherical lenses. It is a nostalgic lens shape.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

Spherical aberration is a full-correction type with a slight bulge to the minus side.

The amount of spherical aberration generated by wide-angle lenses is small because of the narrowness of the light beam. Furthermore, the f/number of lenses is modest at 2.8, so even with a small number of lenses, spherical aberration can be corrected to this degree.

Axial chromatic aberration is generally smaller with wide-angle lenses, so there is not enough of it to be a concern with this lens.

Image Surface Curvature

Image curvature is quite a hefty amount of aberration compared to modern lenses because of this small number of lenses and the lack of aspheric lenses.

However, the image quality seems to be adequate up to the intermediate image height (12mm).

Distortion

Distortion is a little more than 2% at the periphery of the image, so it is well corrected compared to inexpensive zoom lenses.

Chromatic Aberration

Wide-angle lenses tend to have difficulty correcting lateral chromatic aberration, and as expected, the amount is severe because of the small number of lenses.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Let's look at this as a lateral aberration.

The image is beautifully composed up to the mid-image height (12mm), but the periphery of the image seems to be quite tasteful.

The large magnification chromatic aberration in the g-line (blue) seems to be aimed at diffusion by strengthening the halo.

The maximum aperture f/n of such a classically constructed lens is only used to shorten the exposure time, and it is common practice to shoot at aperture one stop down.

Spot Diagram

Spot Scale 0.3 (Standard)

Here are the results of the optical simulation, but let's start with the spot diagram.

The amount of aberration should be large throughout the entire image, but up to the mid-image height, the spots are well dispersed, giving a beautiful impression.

The g-line (blue) aberration is large at the periphery of the image, but it is not noticeable in actual shooting because the aberration is well scattered and its intensity is reduced.

Spot Scale 0.1 (Detail)

This is a rescaled and enlarged view.

It is for comparison with a modern and luxurious configuration of the lens, so this is a bit of a harsh display for this lens configuration.

MTF

Maximum Aperture F2.8

Finally, let's check the results of the simulation by MTF.

The peaks in the center to mid part of the screen are solid and high, and can be expected to be high resolution.

The peak of the mountain in the periphery of the image may be lowered, but the positional shift is also large, so care may be required with flat subjects.

This is a taste that modern lenses do not have, though.

For the small number of lens elements and its compact size, the 28mm F2.8 has generally sufficient performance up to the center of the screen, which I think is a characteristic that has made this 28mm F2.8 a popular lens for a long time.

In today's terms, it should be described as "cost-effective.

Small Aperture F4.0

The resolution seems to improve from the center to the middle of the image, but there does not seem to be much change at the extreme periphery.

Conclusion

NIKON's D series lenses are like old lenses that make use of traditional construction and are easy to obtain even today. I think the reason NIKON has such an important lineup of lenses is because the company, as an optical manufacturer, wanted to preserve its tradition.

As an optical designer, I would rather enjoy the traditional rendering of the D series than appreciate old lenses of unknown origin.

In this blog, we analyze the SIGMA Art series as an example of modern lenses.

For a focal length similar to the NIKKOR 28mm, please refer to our analysis of the SIGMA 28mm F1.4 from the Art series.

 Related article: SIGMA 28mm F1.4

Sample Picture

Example photos are in preparation.

If you are looking for analysis information on other lenses, please refer to the table of contents page here.

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