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Optical Design value Analysis - NIKON AF-S NIKKOR 14-24mm F2.8 G ED Wide[No.032]

This is a performance analysis and review article of the NIKON AF-S NIKKOR 14-24mm F2.8 G

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

Who said that first? The three Fno2.8 telephoto, standard and wide-angle zoom lenses that are favored by professionals are now commonly called Omitsu Motolens.

It is combined with the former Omitsu lens, but the specifications of Dai-Sangen at present (2020) are common to all companies with telephoto 70 to 200 f 2.8 and standard 24 to 70 f 2.8, but wide-angle zoom differs from each company.

For wide-angle zoom, many manufacturers set the focal length range to 16-35mm, but NIKON set it to 14-24mm ultra-wide-angle specification.

This expression is not suitable for the present time, but it is "manly specification".

Since it is a wide-angle zoom, they say, "I don't need the 35 mm side specifications that can be worn with the standard zoom! If you make a 35 mm area, you should make it wider than other companies!" It is truly Nikon-like.

If you take a look at the genealogy of Nikon's F2.8 wide-angle zoom, a total of 3 F2.8 wide-angle zoom has been released including the Z-mount lens which is scheduled to be released as of the time of writing (October 2020).

It started with the first F2.8 zoom Ai AF and the focal length was 20-35mm, but it took about 14 years and the AF-S greatly evolved to 14-24mm specification.

After that, Z mount 13 years later seemed to shift to wider angle specification, but it seems to have evolved to mirror less direction of high performance and miniaturization with the same specification.

In the previous analysis article, we analyzed the latest 14-24F 2.8 for Z-mount, but this time we will analyze the AF-S14-24F 2.8G for F-mount lens of the same specification for comparison.

Private Memoirs

Personally, ultra-wide-angle zoom is a bit of Nigatte field, and its main use is not well understood. Do people like to take pictures of astronomical objects or buildings?

I've heard that people like wide-angle photography as professionals, but I'm an amateur for the rest of my life.

As described in the previous analysis article NIKKOR Z14-24mm, there is a reason to analyze this lens.

In order to verify the true value of the mirrorless lens, which is considered to be advantageous for wide-angle, we analyzed the 14-24mm Z-mount lens of the mirrorless lens last time, so we will analyze this F-mount wide-angle zoom as a comparison partner.

In addition, as the wide-angle lens is a genre in which technological innovation is remarkable, the idea is to investigate how much technological innovation was made in 13 years period from the previous product.

In addition, we will evaluate the performance of this lens itself this time and will produce a comparative verification article of new / old 14-24 lens later.

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NIKON AF-S NIKKOR 14-24mm F2.8 G ED

Document Survey

The number of lenses analyzed is close to 30, so I found the patent easily. Assuming that Example 1 of Japanese Patent Application Laid-Open No. 2007-94174, whose shape is close, is commercialized, the design data is reproduced below.

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 of NIKON NIKKOR 14-24F 2.8 at the wide-angle end.

There are 14 lenses of 11 groups, 3 aspherical lenses for correcting spherical aberration and field curvature, and 2 ED lenses for correcting chromatic aberration. It is a gorgeous Dai-Sangen.

The first Saime is called Maetama.

The first lens is like a super-wide-angle lens with a huge and well-extended eyeballs, and it has a beautiful look that makes you want to look at it forever.

If I buy a lens like this, I have no doubt that I will satisfy my desire to own just by holding and seeing it.

Isn't it "ari" that you buy to decorate your room?

Note : This is the wrong way.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

As you can see from the optical path diagram, a wide-angle lens has a narrow beam of light passing through the center, so spherical aberration and axial chromatic aberration do not become large.

However, the extreme wide-angle specification of 14-24mm may be painful, the aberration is left slightly on the minus side.

It is assumed that this is because the correction of field curvature is insufficient and remains on the negative side, and spherical aberration is intentionally left to achieve overall balance.

Image Surface Curvature

The curvature of field is only a super wide-angle zoom, and the aberration remains on the negative side as a whole, and the peripheral part seems to be a little painful.

Distortion

In the case of a single-focus lens, it is common to limit the distortion aberration to about 3.5% at the maximum. In the case of a cheap zoom lens, it is usually about 5% at the maximum. Therefore, this lens is about 5% at the maximum with an ultra-wide-angle zoom, so it is about the same level as the excellent performance.

Chromatic Aberration

Correction of chromatic aberration of magnification of the c-line (red) It seems that the g-line (blue) is superimposed on the remainder to relax the appearance, but considering the specification of super wide angle and large diameter, it can be said that it is doing quite well.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Let's look at it as a transverse aberration.

Although it has a large aperture, it gives a clean impression. If you look at it in detail, it leaves a little spherical aberration in the center, so there is a little violence, but the sagittal image is completely suppressed, and the aberration is sufficiently suppressed compared to the single focus one time ago.

Spot Diagram

Spot Scale 0.3 (Standard)

This is the result of optical simulation, but first let's look at the spot diagram.

Although the c-line (red) seems to be a little strong, since there are few sagittal frames, the spot shape remains rounded and gives an ideal atmosphere.

Spot Scale 0.1 (Detail)

This is the enlarged spot diagram with the scale changed.

MTF

Maximum Aperture F2.8

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

The height of the peak from the center to the middle part of 12 mm shows high performance. If the height exceeds 18 mm, the position (focus) of the peak may be out of focus, but the height of the peak remains high enough to maintain sufficient resolution up to the periphery.

The degree of residual spherical aberration at the center and subtle waviness of lateral aberration are balanced appropriately in consideration of the overall performance.

Small Aperture F4.0

Focusing on F4 dramatically reduces the out-of-focus in the peripheral area. With such resolution in spite of ultra-wide-angle zoom, there is nothing to complain about when it is used in film.

The performance of the open F2.8 must have been decided after all the calculations so far.

Conclusion

I thought that the strictness of the performance came out because of the specification of the super wide angle and large diameter 14 to 24 mm F2.8, but I found that the high performance that far exceeds the cheap standard zoom is realized by high aspheric surface manufacturing technology and sophisticated aberration correction technique.

I think it is a part of Daisangen.

The telephoto end (24 mm) side will continue to the next article.

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NIKON AF-S NIKKOR 14-24mm F2.8 G ED

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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