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The Ultimate Guide to the SIGMA 24mm F1.8 EX DG vs SIGMA 28mm F1.8 EX DG - Optical Design Value Analysis No.065

This is a performance analysis and review article of the SIGMA 24mm F1.8 EX DG vs SIGMA 28mm F1.8 EX DG.

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

SIGMA EX Lens is a series of high-class lenses for professional and Hi-Am started in 1998.

As of writing (2021), the Art line of high-end lens series at SIGMA has been sold since 2012, but is it easy to understand if I say its predecessor?

This time, we will analyze two of the EX series, the 24 mm F1.8 EX DG and the 28 mm F1.8 EX DG, which were popular because of the F1.8's large diameter but reasonable price.

It seems that this lens was really popular. It was released in 2001, but I remember that new ones were available until around 2019. Does it mean that it was loved for a long time?

Especially, the 28 mm focal length single-focus lens was not released as a successor, and it was not until 2019 that the 28 mm F1.4 was released from the SIGMA Art line.

In the past, our blog also analyzed the successor 28 mm F1.4 Art.

Also read: SIGMA 28 mm F1.4 Art

Well, the 24 mm F1.8 EX and the 28 mm F1.8 EX were released at about the same time, but these two lenses have a strange feature.

Amazingly, the lens configurations look almost identical, like twins.

When you hear the difference between lenses with focal lengths of 24 mm and 28 mm, you may be misled into thinking, "Maybe there isn't much difference?" However, the contents of ordinary lenses differ greatly from each other. Even the fact that the number of lenses is the same may be unusual.

In order to quietly analyze the secrets of the mysterious twin lens, I decided to compare and analyze the two lenses together.

Document Survey

Actually, I also owned SIGMA 24 mm F1.8 ex DG for a period of time, and I was researching the past patent literature as an analysis theme someday.

At that time, Japanese Patent Application Laid-Open No. 2001 / 330771 was discovered, and according to the embodiments in the document, embodiments with focal lengths of 24 mm and 28 mm were described.

In general, patent documents often contain various embodiments, so I didn't think it was particularly strange at first.

However, I remembered that there was a similar product of this 24 mm lens with a focal length of 28 mm, and when I investigated again, I found that the composition of the two lenses was similar at a level where you cannot tell the difference at a glance.

And I noticed that the two lenses were combined in one patent.

Judging from the fact that only one patent was granted and the timing of the product's release, we believe that the two lenses were designed by the same person at the same time.

However, if the same person designs at the same time, he or she will have to carry out various tasks and events in the subsequent development at the same time, so it is usually likely to go flat.

Of course, multiple people share the work and perform load balancing, but there are many things that only the person who designed it can understand, so simple distribution does not work well.

Therefore, I assume that you had a great deal of trouble in producing this twin, but in order to show respect for this, assuming that Example 2 and Example 3 were commercialized, the design data will be 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 the 24 mm f / 1.8 ex on the left and the 28 mm f / 1.8 ex on the right.

Each consists of 9 groups and 10 lenses, and the 3rd and 6th lenses are aspherical lenses.

They are very similar at a level where it seems difficult to tell one from the other when suddenly shown off.

Now you might ask, "Why did you make it so similar?"

Probably, the aim was to keep the price of the entire product low by thoroughly standardizing the mechanism and so on, wasn't it?

A general lens has a different composition depending on the level you can see, so every part adopts a special part customized for each product.

On the other hand, I think this lens embodies the "spirit of SIGMA" to lower the price of the product by standardizing all parts except the lens.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

Let's take a look at the spherical aberration. It's a large aperture F1.8 lens, but it doesn't look too big because it's a wide-angle lens, so it seems to be well compensated.

By the way, the top of the graph is truncated, and it is unknown whether it is a bug of Optalix or not, but since it is the same as the characteristic of the patent document, it seems that there is no problem with the characteristic itself, only the top is wide and empty due to the problem of graph drawing.

Axial chromatic aberration has a slightly larger feel, but it overlaps well at the top of the graph and doesn't bother Fno on the open side.

Field Curvature

The tangential direction (broken line) of the field curvature is considerably deviated around the 21 mm image height at the upper end of the graph.

Since this lens was released in 2001, it is practically for film shooting, so it is reasonable at this level.

Generally, when film is printed, the corner of the screen is cut due to the print paper, so ordinary level photographers do not have a chance to see it.

Distortion

The distortion aberration leaves a so-called barrel shape deviation that expands to the minus side, but it is a moderate level considering the era and price.

Lateral Chromatic Aberration (Magnification Chromatic Aberration)

Lateral chromatic aberrations is an aberration that tends to be severer as a wide-angle lens, but as you say, 24 mm is a little bigger overall.

For that reason, in general, the wide-angle lens has more lenses, but since this lens has the same number of lenses, as a result, the performance of the 24 mm lens is more difficult.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Let's look at it as Transverse Aberrations.

The aberration in the sagittal direction is at a similar level for both of the two, and it is a rather bold performance.

The tangential direction is summarized at a level that is not much inferior, but you can see that the 24 mm focal length is more painful.

Spot Diagram

Spot Scale 0.3 (Standard)

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

Up to the image height of about 15 mm in the middle of the screen, they compete with each other, but the spot size with a focal length of 24 mm on the outside of the screen is two times larger than this.

Spot Scale 0.1 (Detail)

MTF

Maximum Aperture F1.8

Finally, let's look at the results of the MTF simulation.

The focal length of 24 mm is a little bit higher up to the image height of 15 mm in the middle of the screen, but if you look at the total such as the degree of coincidence of the positions of the mountains, the focal length of 28 mm is clearly better.

If you don't care about the resolution of the corners, the center has enough performance to be used even in modern times, and the slightly retro description may be nostalgic.

Small Aperture F4.0

Conclusion

SIGMA's mysterious twin lenses, if you look closely, it can be said that it is a philosophical lens that gives a glimpse of "SIGMA's spirit".

In addition, I am also grateful for SIGMA's technical ability to finish two of these at the same time.

Now, the question is, which lens do you choose?

I personally recommend the 28 mm focal length for standard performance, and the 24 mm focal length for a slightly playful look.

In addition, we analyzed the 24 mm and 28 mm focal length lenses of the Art line, which can be said to be the successor of each lens, in the past, so if you look again, you will enjoy the evolution of it.

Also Read: SIGMA 24 mm F1.4 Art DG HSM
Also Read: SIGMA 28 mm F1.4 Art DG HSM

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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