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Optical Design value Analysis - NIKON AI AF NIKKOR 35mm F2.0D [No.026]

This is a performance analysis and review article of the NIKON AI AF NIKKOR 35mm F2.0D

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

The NIKON 35 F2D is a long-selling product that has been on the market since 1995. In order to investigate the optics of this lens, we first look at the genealogy of past NIKON 35mm F2 specification lenses, which is as follows.

Number of 35mm F2 lenses and year of release

  • New Nikkor 35mm F2(1975)6/8
  • Ai Nikkor 35mm F2(1977)6/8
  • Ai Nikkor 35mm F2S(1981)6/8
  • Ai AF Nikkor 35mm F2S(1989)5/6
  • Ai AF Nikkor 35mm F2D(1995)5/6

groups/elements

When the F2S was converted to autofocus (AiAF), the optical system seems to have been changed from an 8-elements-in-6-group configuration to a 6-elements-in-5-group configuration. When simply described as F2S, this lens becomes two types with or without autofocus, and each seems to have a different optical system. This is confusing. If you look online, you will find numerous articles on various misunderstandings.

The lens we will discuss here is the 35mm F2D, which is still sold today, but its optical system consists of 6 elements in 5 groups, the same as the autofocused Ai AF F2S, and has been used since 1989.

In our blog, optical systems designed in the film era are treated as old lenses, so this is an old lens that continues to be sold even today.

In terms of appearance, it has a strong plastic feel and looks cheap (although it is in fact inexpensive), but if you are accustomed to seeing SIGMA's Art lenses and other recent products with a strong metal, heavy, and luxurious feel, this product has a retro futuristic look that is similar to a radio-cassette player from the 1980s.

Private Memoirs

In the film era, f/2.8 was the standard for 35mm lenses, and f/2.0 was a higher grade of high-end specification, but by the end of the film era, lenses with f/1.4 specifications began to increase, making them relatively affordable.

Furthermore, in recent years, 35mm F2.0 lenses are usually the second or third cheapest single focal length lenses, so they have become "something you just have to buy along the way.

If you share this feeling, you are "neck-deep in the lens swamp.

Aside from the fact that film-era photography was based on fixed ISO sensitivity, the brightness of the focal length (Fno) was a major determinant of the degree of freedom of photography, so even F2.0 lenses had a high degree of advantage.

Furthermore, the angle of view of 35mm is a wide-angle range where camera shake is less noticeable, and it can be managed even if the shutter speed is slow when shooting.

When shooting in the evening or indoors, having a zoom lens and this compact 35 F2 lens was a good insurance policy without increasing my luggage.

Therefore, I used to treat the 35mm F2 lens as "a lens that I bought for some reason and kept in my camera bag for some reason.

As time went by and we entered the digital age, SLR cameras for ordinary people started using APS size image sensors, so even if I wanted to use the old Gauss 50mm F1.8 as a standard, it became a medium telephoto equivalent to the full size 75mm, which changed its usability.

So I decided to use the 35mm F2 lens that I have for some reason, which is equivalent to about 50mm on a full-size equivalent, which is very easy to use, and it is inexpensive because it has been around for a long time! And it is inexpensive because it has been around for a long time!

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NIKON AI AF NIKKOR 35mm F2.0D

Document Survey

However, when I checked the lens configuration again, I noticed that the optical system had been updated at the time of the AF F2S. Then, I searched in the vicinity of the AF F2S release date of 1989, and finally found Patent Publication 2-51115. Let me reproduce Example 1 by looking at the design values.

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

The above figure shows the optical path diagram of the NIKKOR 35mm F2.0 D.

It consists of 6 elements in 5 groups, with a concave lens on the first lens on the subject side and a lens group like a variant of a Gaussian lens placed a little further away on the image sensor side.

This configuration, in which a concave lens or a lens group with a strong negative focal length is placed on the subject side, is called a retrofocus type and is considered the basic configuration of wide-angle lenses for single-lens reflex cameras.

The focal length is the length from the lens to the image sensor in the case of a single lens, and a wide-angle lens is defined as "a lens with a short focal length = a lens with a short overall length. This requires a longer overall length.

To achieve this, a strong concave lens is placed on the subject side to extend the back focus, but from the standpoint of simple physical laws, this is an unnatural optical system, and as a result, "aberration correction becomes difficult.

As a result, the f-no can not be as bright as that of a 50mm lens, and the number of lens elements tends to increase, making the lens heavier and larger than a 35mm lens, which is an issue for lenses wider than 35mm.

Incidentally, the optical system for rangefinder cameras, as typified by Leica, can have a short back focus, so a symmetrical optical system with a concave lens on the image sensor side can be used, allowing for greater design freedom.

An easy example would be Biogon. I would like to discuss rangefinder lenses in depth in another article.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

The spherical aberration is full-correction type with a slight bulge to the minus side, but it does not give a strong impression. As one would expect from a product of the Heisei era, the lens is well designed despite the small number of elements.

I have analyzed the Zuiko 35mm F2 in a previous article, but since this lens is about 20 years older than the Zuiko 35mm F2, the spherical aberration is probably twice as high.

On the other hand, as a modern lens, the SIGMA Art 35mm F1.4, although it has a different Fno, will give you an idea of the difference in performance.

Image Surface Curvature

Image curvature seems to have a large difference between sagittal and tangential at the extreme edges of the image, but it is balanced up to the middle of the image.

Distortion

Distortion will remain to be corrected slightly, but it is less than half that of inexpensive all-in-one zoom lenses.

Chromatic Aberration

The magnification chromatic aberration is nicely integrated given the small number of lens elements. Aperture down and MTF improvement will be highly effective.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Let's look at it as a lateral aberration.

The flare in the sagittal direction (right column) is quite severe. This is the flavor of the lens, but if you stop it down by one stop, you will enjoy the sharp increase in resolving power.

In the tangential direction (left column), the halo component of the c-line (red) is large from the middle of the image and is a little worrisome.

Spot Diagram

Spot Scale 0.3 (Standard)

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

Although we were concerned about the halo effect of the c-line (red), the aberration itself is too large and seems to be diffused, so the red blur will not be noticeable in actual shooting. It is even less noticeable because it is cut off when the aperture is stopped down. Excellent aberration correction.

Spot Scale 0.1 (Detail)

This is an enlarged spot diagram with the scale shown changed.

This is prepared for comparison with modern lenses, but the scale is a bit harsh for lenses of this era.

MTF

Maximum Aperture F2.0

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

As is characteristic of image curvature, the tops of the peaks are aligned up to the middle part of the image.

The discrepancy is large at the periphery, but since it is only at the four corners, it is not a concern unless you are shooting stars or other objects.

Small Aperture F4.0

It would be fun to compare the MTF improvement with actual shooting.

Naturally, lenses of this era are designed to perform at their best when stopped down about one stop, which is what we are aiming for.

Conclusion

NIKON's D series lenses are not so much old as they are still being sold in the 2000s.

However, they are typical products of an optical manufacturer that employs classic optics and retains a "flavor" that modern lenses do not have.

This lens is filled with NIKON's desire to preserve good traditions in the modern age.

NIKON is a world-class optical equipment manufacturer.

I would recommend purchasing a NIKON D series lens rather than paying a lot of money for an unknown old lens.

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NIKON AI AF NIKKOR 35mm F2.0D

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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