NIKON

Optical Design value Analysis - NIKON AiAF NIKKOR 50mm f/1.4D [No.018]

This is a performance analysis and review article on the Nikon Nikkor 50 1.4D.

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 them 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, which are generally unseen, and explain the taste and descriptive performance of lenses in a deep and gentle manner.

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.

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

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

This is the third installment of the series. Previously, we analyzed the slightly darker f/1.8D and f/1.8G lenses, but this time it is the f/1.4D, which is a brighter specification.

This f/1.4D lens seems to have no optical design change from the New Nikkor 50mm f/1.4S (released in 1976).

The f/1.8D optics were originally appropriated from a product released in 1978, so the f/1.4D seems to be slightly older in origin.

Private Memoirs

In the 1980s, at the end of the era of manual-focus SLR cameras, 50mm F1.4 lenses were sold by various companies, and I believe that F1.4 lenses were treated as "true standard lenses. My first SLR camera lens was also an F1.4 lens.

However, as lenses became larger and more expensive with the introduction of autofocus, and zoom lenses were treated as standard lenses in terms of sales, F1.4 lenses became a shadow of their former self…

The F1.4 lens became a shadow of its former self, as the cheaper and smaller F1.8 lens was positioned as the standard lens for entry-level single focal length photographers.

In addition, at the dawn of the digital age, APS size sensors were the mainstream, so the long focal length of 50mm itself became a subtle existence for APS cameras, but as full size sensors became less expensive and the culture of loving bokeh spread around the world, the 50mm f/1.4 became the standard focal length lens. However, as the price of full-size sensors became lower, the 50mm f/1.4 focal length was reevaluated and redeveloped in around 2015.

The Gaussian type is perfect for SLR cameras with mirrors, but I wonder if the zonar type used for short backs will be revived when the entire company goes completely mirrorless in the future.

Document Survey

Unfortunately, I could not directly find any patents that seem to be design values for this lens. I do not know if the age of this area is not yet digitized or if there is a lack of research since the patent documents were made before and after the electronic filing of patent documents.

However, there was a document that is quite close in composition, so I will analyze it assuming that Patent Publication No. 57-161822 is probably close in performance. This document was filed about five years after the product was launched, so it is clear that it is not a design value. However, if the configuration of the deformation part is the same for a Gaussian deformation type optical system, the performance should be very similar.

Assuming that Example 1, which looks very similar, is the design value, 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 50 F1.4D.

It consists of 7 elements in 6 groups, and one convex lens is added on the image sensor side of the symmetrical Gaussian lens.

The aspherical lens is not used; it would be more appropriate to describe the f/1.8D as having an additional convex lens on the image sensor side.

There is nothing special to note about the lens material, but the f/1.8D uses only two types of material in a symmetrical arrangement, while the /f1.4D uses five types.

As f/1.8D has a larger aperture, it is difficult to correct spherical and chromatic aberrations even with Gaussian-type lenses, and the symmetrical structure can no longer be maintained, and this can be seen in the material arrangement.

As explained at the beginning of this paper, we could not find any patent document that seems to be the design value of this product.

This design example is a lens with a similar configuration to the 50mm f/1.4D, which was filed by NIKON several years after the product was launched.

The subtle shape and materials of the lens are different from those of the product.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

As an F1.4 large-aperture lens from about 40 years ago, I thought that the amount of spherical aberration and axial chromatic aberration would be quite large, but they are reasonably well controlled.

Image curvature has been corrected to a reasonably small degree, and spherical aberration has been corrected to near zero in the mid-range, so you can enjoy a fluffy feel when the lens is wide open, and performance increases sharply when it is stopped down.

In our blog, we analyze SIGMA's Art series as a reference for modern lenses, and there is a 50mm F1.4 lens with the same specifications, but it has about three times the amount of SIGMA's lens aberrations.

Naturally, SIGMA lenses have a large number of components, weight and price are also very respectable.

Image Surface Curvature

The difference between sagittal and tangential image curvature is small up to the middle of the image, and the difference opens up at the edges of the image, a characteristic typical of Gaussian types, but the absolute value is not large.

Distortion

Distortion is slightly barrel-shaped, but is characteristic of symmetrical Gaussian types and is in the small range in absolute value.

Chromatic Aberration

The face of the f/1.8D graph is different from that of the f/1.8D graph, which is probably due to the shift from a symmetrical structure.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Let's look at it as a lateral aberration.

The difference between the leading edge and the middle part of the image shows the degree of blur, but even just looking at the center of the image (the bottom graph), it is probably 1.5 times larger than that of f/1.8D. The open aperture is probably much fluffier.

Spot Diagram

Spot Scale 0.3 (Standard)

Let's start with the spot diagram, which shows the results of the optical simulation.

The spot on line c (red) is corrected to be small, and the flare on line g (blue) looks good.

Spot Scale 0.1 (Detail)

Here is a spot diagram with the scale changed and further expanded.

MTF

Maximum Aperture F1.4

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

Compared to the f/1.8D, the MTF drops by about 20 points from the center to the middle region where the image height is about 18mm.

Small Aperture F1.8

This time, the MTF was calculated with the lens stopped down to f/1.8 in comparison with f/1.8D and f/1.8G. The amount of improvement is considerable, and the MTF near the center of the screen exceeds that of the f/1.8D and is close to that of the f/1.8G.

Small Aperture F4.0

Although high enough, it is not much different when compared to the small f/4.0 aperture of the f/1.8D.

The basic characteristics of Gaussian-type lenses are that spherical aberration is in full correction form and that lateral chromatic aberration is abnormally small, and as a result, MTF improves abnormally when the aperture is stopped down.

As a result, MTF improves at small apertures, even with a lens with a slightly unreasonably bright maximum aperture Fno, and the image becomes crisp and clear.

Conclusion

This beautiful lens achieves f/1.4 with a small number of lenses, partly due to the basic performance of the Gaussian type. The maximum aperture is quite fluffy and low-resolution, but when stopped down to f/1.8, the performance is close to f/1.8G, and at f/4, there is no difference between this lens and modern lenses.

It can be said that one lens is good for both. In this way, even old lenses can be enjoyed in various ways if their characteristics are kept in mind, and this is probably the deepest aspect of playing with lenses.

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.

-NIKON
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