NIKON

Optical Design value Analysis - NIKON NIKKOR Z 50mm f/1.8S [No.021]

2022-07-31

This is a performance analysis and review article on the Nikon Nikkor Z 50 1.8 S.

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

Even if you check magazines and the Internet, you probably only find similar "word-of-mouth recommendation" 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.

You may find a good lens, a bad lens, a famous lens, a peculiar lens, or a lost lens for you.

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

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 to change the optics as well?

In the previous article, we took a look at the 58mm F/1.4G released in 2013 and discussed its 3-dimensional high-fidelity design, but it was "too difficult to understand…" (see below). This time, I will finally analyze the Z 50mm f/1.8S, the standard lens for full-size mirrorless lenses.

I have persistently explained that the standard 50mm lens is "Gaussian." However, with a mirrorless camera lens, there is "no mirror in front of the image sensor," so it is possible to have a short back focus structure that allows the lens to be placed right up to the edge of the image sensor.

The traditional double-Gaussian configuration should finally become unnecessary. What will happen now? That is the point to pay attention to.

Private Memoirs

In 2018 NIKON finally entered the full size mirrorless market. Although the camera industry was in the doldrums, Sony and others were still going strong, and it was impressive that they came out with a flashy product announcement event in a year when there still seemed to be a chance for them to make a big splash.

I watched the live video on YouTube at the time, and I remember that the NIKON executive was trying to explain the product in a way that sounded like an imitation of Steve Jobs.

I remember that NIKON executives were trying their best to imitate Steve Jobs in explaining the product.

Along with the shift to mirrorless lenses, the F-mount, which was said to be unchanged, was finally changed and a new lens system was introduced as the Z-mount.

Although it was always said that the F-mount would remain unchanged, it was difficult for beginners to understand because there were various derivative versions due to the additional structure, so I think the change to a new mount was a good thing.

In addition, we should not forget that at this time, NIKON's first mirrorless camera, NIKON1, which was practically finished, also disappeared officially.

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NIKON NIKKOR Z 50mm F1.8S

Document Survey

I found the published lens configuration diagram and Vitali's patent information, example 9 in WO2019/220618. I immediately tried to reproduce it, but there seemed to be something wrong with the description and it did not match the disclosed near-axis values… NIKON, "What if…"

After checking, I found that the interval values in some places were wrong and managed to correct them.

I don't think I copied it wrong, but I was able to reproduce the design values, so let's take a look at the performance as soon as possible.

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 Z 50 F1.8S.

It consists of 12 elements in 10 groups, with aspherical lenses used for the 4th and 8th lenses shown in red.

Since this is the first generation of mirrorless lenses, I thought it would have a distinctive cross-section, but to my surprise, the center of the lens is "Gaussian! Gaussian after all.

It looks as if a negative focal length converter is attached to the front and rear of the Gaussian lens.

The number of lens elements is equivalent to that of the Sigma Art 50mm, with more aspherical lenses than the Art, and the Fno is 1.8, making it the ultimate in luxury design.

Although it is a complicated configuration, it can be said to be a symmetrical optical system since the negative lens groups are arranged in front of and behind the Gaussian.

However, this configuration has never been seen before, so it must mean that a new type based on Gaussian was invented.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

Both spherical and axial chromatic aberrations are suppressed to near-extreme levels.

It seems that the aberrations have been suppressed purely, changing the direction from that of the 58mm f/1.4, which is for taste.

Image Surface Curvature

The image curvature is also simply smaller, perhaps less than half that of the relatively new f/1.8G released in 2008.

Distortion

Distortion is at a level that can be called almost zero, probably thanks to the symmetrical structure of the negative lens group added before and after the Gaussian.

Chromatic Aberration

The magnification chromatic aberrations of the c-line (red) and f-line (light blue) up to the middle image height are minimally corrected, and even at the top of the graph and at the most peripheral image heights, they are quite small.

At first glance, line g (blue) appears large, but this is not a problem because of its low visual sensitivity.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Let's look at it as a lateral aberration.

It is just so small…

Even the SIGMA Art 50mm F1.4 is surprisingly high performance, but at Fno1.8, even though it is a little darker, it is even smaller than that, and the amount is miniscule.

Spot Diagram

Spot Scale 0.3 (Standard)

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

If you look at it on a standard scale, you can see that most of the entire screen area is an abbreviated "spot", which is a different dimension from the traditional Gaussian-type 50mm f/1.8 of the past.

Spot Scale 0.1 (Detail)

Here is a further magnified view.

Scattering is only slightly noticeable from the 18mm image height on the periphery of the image, and a high level of resolution can be expected from the wide open aperture state.

MTF

Maximum Aperture F1.8

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

As per the few aberrations, it is bisically high from the open fno state.

I have analyzed various old Gaussian types in my past articles, and compared to the standard configuration, the height of the MTF peak at the peripheral image height has improved to about twice as high.

Small Aperture F4.0

It can be said to be an ideal lens, with no sense of aberration even at the extreme periphery when stopped down to F4.

Conclusion

Isn't it the birth of a dream ultra-high-performance single focal length with almost completely corrected aberrations?

This is the latest and greatest standard lens that NIKON has put its prestige (or so it seems) on, and it is super high performance. The price is also very reasonable, and I feel that it is a bargain.

It is the very embodiment of a standard lens for the new era of mirrorless lenses.

While more and more products rely on electronic aberration correction by image processing, NIKON is indeed a world leader in providing ultra-high-performance products to the world using pure optical technology alone.

I can't wait to try it out…

However, there is one thing that concerns me. If this F1.8 lens is so ultra-high-performance, what kind of line will the F1.4 specification lens that is expected to be released in the near future have?

If it goes the ultra-high-performance route, there will be no difference from the F1.8 lens, so will you differentiate it as a bokeh-oriented route like the 58mm f/1.4 lens? I am rather curious about the next product.

Amazon Product Link
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NIKON NIKKOR Z 50mm F1.8S

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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