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Optical Design value Analysis - NIKON AF-S NIKKOR 58mm f/1.4G [No.020]

2022-07-23

This is a performance analysis and review article on the Nikon Nikkor 58 1.4 G.

You hardly know how the lenses work, how their performance differs from each other, and the specific differences between them.

Even if you look it up in magazines or on the Internet, you probably only find similar "word-of-mouth recommendations" 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 that are not generally visible, and explain the taste and descriptive performance of lenses in a deep and gentle manner.

Please enjoy the special information that you can read only on this blog in the world.

Overview

In commemoration of the discovery of the NIKKOR Z 58mm f/0.95 S Noct patent documents, we have decided to proceed with a series of analyses of the NIKKOR 50mm. In short, this is a project to enjoy the history of NIKON lenses on my own.

First of all, as of 2020, the following NIKON 50/58mm lenses are currently available.

  • AI AF NIKKOR 50mm f/1.8D
  • AF-S NIKKOR 50mm f/1.8G
  • AI AF NIKKOR 50mm f/1.4D
  • AF-S NIKKOR 50mm f/1.4G
  • AF-S NIKKOR 58mm f/1.4G
  • Ai NIKKOR 50mm f/1.2S
  • NIKKOR Z 50mm f/1.8 S
  • NIKKOR Z 58mm f/0.95 S Noct

Eight of them…that's a menace. And each of them seems to have a different optical system.

It is understandable if the motors, drive mechanisms, electromagnetic aperture, etc. are different, but why bother changing even the optics… This is partly because it is the dawn of the mirrorless era, but how much does NIKON love 50mm?

This is the fifth article in the series. In the previous article, we analyzed the 50mm f/1.4G released in 2008, and this time we will focus on the 58mm f/1.4G released in 2013 with a slightly different focal length.

I believe that this semi-focal length is in respect to the Nikkor-S Auto 5.8cm f/1.4 and the AI Noct Nikkor 58mm f/1.2.

At the time of this product's release, at events and in articles introducing the product, the optical design was explained as "a 3-dimensional high fidelity design. I was impressed by the buzz in various places.

I did not understand what he was talking about at the time, but I may be able to understand it by looking at the design values again.

Private Memoirs

When the 58mm F1.4 was launched in 2013, my personal buzzword of the year was "3-D hi-fi". At work, I could just say "3-D hi-fi" for anything and everything…I miss it.

The following year, the SIGMA Art 50mm F1.4 was released, and I forgot all about hi-fi.

The NIKKOR 58mm and SIGMA 50mm were coincidentally released at the same time as standard lenses of the new era representing their respective companies.

Although they have different design concepts, they were both released at the same time.

If you call yourself a 50mm lens lover, these two lenses are a must-have.

In this article, we will analyze the 58mm lens by itself, but we plan to write an article comparing these two lenses at a later date.

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NIKON AF-S NIKKOR 58mm F1.4G

Document Survey

We were unable to find any patent information that exactly matches the published lens configuration diagram, but since the name of the designer of this product is also published by NIKON, we found a patent that seems to be close to the product in terms of author information and examples of use, based on a comprehensive review.

Patent Publication 2014-13297 was a document that seemed to be close in application date and configuration.

It is assumed that the features of the product are included in this patent, and therefore, a new application was not filed.

If the optical system is a Gaussian deformation type, if the configuration of the deformation part is similar, the performance should be very similar, so the essence of the product can be fully felt. Therefore, assuming that the design value is Example 1, which looks very similar, let us reproduce the design data as follows.

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 58 F1.4G.

It consists of 9 elements in 5 groups, with aspherical lenses used for the 3rd and 9th lenses shown in red. The structure has changed considerably, although the double-Gaussian configuration retains its vestiges.

No special materials are used for the glass.

As explained at the beginning of this article, the actual product is not a perfect match.

The shape of each lens is approximately the same, but the fifth and sixth lenses are not joined. The aspherical lens on the subject side above the aperture is the first lens, and the aspherical lens on the image sensor side above the aperture is the ninth lens.

The product configuration may have smaller spherical aberration because the aspherical lenses are positioned closer to the first plane and the aperture plane, where the on-axis light flux is higher.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

The spherical aberration appears to be corrected to a fairly small amount at first glance, but it has a peculiar shape in which the middle part of the graph extends to the positive side and the tip part warps to the negative side, and when viewed as the difference between the middle and tip parts, the amount of aberration is not much different in absolute terms from the old 50mm f/1.4G lens.

This is a strange aberration that could be taken to be the opposite of a typical Gaussian lens, and this is probably what adds flavor to the bokeh image in this 3-dimensionally high fidelity area.

Does the fact that spherical aberration has both positive and negative deviations mean that both foreground and background bokeh will have similar bokeh images?

On-axis chromatic aberration is not significantly different from older products, etc.

Image Surface Curvature

Image curvature is a little larger, but about the same as 50mm f/1.4G.

Distortion

Distortion is slightly barrel shaped, but this is probably due to the symmetrical Gaussian type being broken up. It is not an amount to be concerned about in absolute terms.

Chromatic Aberration

The lateral chromatic aberration is uniform throughout the image, but is adequately corrected; it is not the type that worsens on the periphery of the image, as is the case with the 50mm f/1.4G. If the emphasis is on bokeh, it is probably with the intention of minimizing lateral chromatic aberration, which outlines the bokeh image, as much as possible.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Let's look at it as a lateral aberration.

Compared to 50mm f/1.4G, the amount of sagittal aberration is drastically reduced.

At intermediate image heights, the aberration does not seem to be produced by the sagittal flare that is familiar in Gaussian types to bring the image into focus.

I wonder if this is the way it is summarized because it is thought that 3-dimensional high fidelity is to make the aberration uniform in the focus direction to make the bokeh smooth and even…

In the tangential direction, the purely coma aberration is reduced to about half.

Spot Diagram

Spot Scale 0.3 (Standard)

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

The spot is small enough, but especially inside the image height of 12mm, the spot remains quite round, even when the spot is shifted in focus to the left or right. This is also a 3-dimensional high fidelity area.

Spot Scale 0.1 (Detail)

MTF

Maximum Aperture F1.4

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

As for MTF, there is not much difference from the old product in the center of the screen, but the peripheral area has been improved to a much higher level. Although the emphasis is on bokeh, the resolving power also seems to be at a sufficient level for a modern lens.

Small Aperture F4.0

The MTF improves dramatically when stopped down to F4.0 because the aberration at maximum aperture is corrected to a small degree, but the image curvature becomes stronger at the periphery.

However, the MTF improves dramatically when stopped down to F4.0, but the image curvature becomes stronger at the periphery.

Conclusion

I think that the three-dimensional high fidelity can be expressed simply as "smooth bokeh" by pursuing roundness of the spot while minimizing sagittal flare to an extreme degree.

It seems that the photographer sought to optimize two contradictory phenomena at the same time, namely, pursuing bokeh while also placing importance on improving resolution, but the characteristic and novel sagittal characteristics of spherical aberration and lateral aberration make it difficult to imagine the actual image in my mind.

However, when I looked at the actual image, I was able to get a glimpse of their intention.

In a way different from aberration, this lens has very little so-called "two-line blur.

The two-line blur is a phenomenon in which a double outline appears in a blurred image, and it is generally considered unnatural and unsightly.

I noticed that the bokeh image is smooth and beautiful because of the lack of this two-line blur.

The aim of this product was to achieve this naturally melting bokeh effect, and I am impressed that NIKON would plan and release this lens in addition to the two 50mm F1.4 lenses with similar specifications that are already on the market.

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NIKON AF-S NIKKOR 58mm F1.4G

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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