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Optical Design value Analysis - SIGMA 28mm F1.4 DG HSM Art [No.012]

2022-04-17

This is a performance analysis and review article of the Sigma Art 28 F1.4.

You hardly know how lenses work and how their performance differs from each other.

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, we will examine the history of lenses and their historical backgrounds, while estimating lens design performance based on patent information and actual shooting examples, and analyze lens performance in detail from a technical perspective through simulations.

Professional lens designer Jin Takayama carefully unravels optical characteristics such as optical path diagrams and aberrations, which are not generally visible, and explains 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

SIGMA's Art lens series is a flagship model that combines a high-quality appearance with metal parts and high resolution performance.

The 24mm F1.4 DG HSM Art lens introduced in this section is a large-aperture wide-angle lens that boasts extremely high resolution performance.

It is the latest wide-angle lens in Sigma's Art large-aperture single focal length series. (As of writing in 2020)

This lens is described as a "classic focal length" on Sigma's website.

It is true that in recent years, we rarely hear of 28mm focal length specifications, but what is the true meaning of "classical"?

I think that in recent years, the wide-angle end of zoom lenses has been starting at 24mm, which has led to a decrease in the number 28mm, which may give the impression of a classical lens.

In addition, the recent trend toward the supremacy of bokeh may also have influenced the fact that the focal length is not so bokeh, nor is it an ultra-wide angle lens, so it is difficult to create a distinctive feature, and the number of lenses with this lens has decreased dramatically.

Putting speculation aside, expectations are high for the performance of this lens, the last of the wide-angle lenses to be released.

Private Memoirs

This is the focal length that served me very well as a gateway to wide-angle lenses when I was a teenager starting out in photography. I remember that the first zoom I purchased a while later also had a 28mm wide-angle end.

Perhaps because of this, I still find 24mm difficult to use, and I always wish that the wide-angle end of today's zoom lenses was also 28mm…

Now, continuing from the article on the SIGMA 35mm F1.4 Art, I will analyze the Art series single focal lengths.

This is part of our effort to establish a benchmark for modern optical design values, since SIGMA's Art single focal length lenses are designed with a very straightforward concept of "performance-oriented, size-neutral" and are therefore easy to use as a benchmark standard.

The analysis of the telephoto side has been completed up to 135mm in the previous article, and we will now move on to the wide-angle side.

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SIGMA 28mm F1.4 DG HSM Art

Document Survey

Now, when I checked the patent literature, it was easy to find patents that I thought were relevant since this is a modern product.

Looking at the details, although the shape is different from the one shown on the website, it seems that the shape is closest to that of the patent application 2019-219472 Example 4, so I will assume this is the design value and reproduce the design data 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

Above is the optical path diagram of the SIGMA Art 28 F1.4.

The lens has 17 elements in 12 groups, three aspherical lenses, and three special low-dispersion materials for good correction of chromatic aberration.

It is rare to find a single focal length lens with three aspherical lenses. It is also the largest number of elements among the lenses discussed in this blog so far.

There are many aspherical surfaces, and inputting the data was tedious… Moreover, I spent a lot of time with mysterious calculation errors, probably due to a problem with the analysis software I use, OPTALIX. Tired…

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

The Art series itself touts high performance, and being a latecomer among them, spherical aberration and chromatic aberration on axis are well suppressed. There is no longer any need for comment.

Image Surface Curvature

There is no longer a "sickening" level of distortion…

Did the person in charge of this design have some traumatic experience with distortion?

If it were me, I would rather correct image curvature more than correct distortion to this extent, but image curvature is not so large as to be called large, so it is just a matter of difference in sensitivity.

Distortion

The lateral chromatic aberration is also well corrected.

The difference in distortion by the wavelength of light can be called lateral chromatic aberration, so it is possible that lateral chromatic aberration has been suppressed by making the distortion extremely good.

Chromatic Aberration

The lateral chromatic aberration is also well corrected.

The difference in distortion by the wavelength of light can be called lateral chromatic aberration, so it is possible that lateral chromatic aberration has been suppressed by making the distortion extremely good.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Generally, the wider the lens, the greater the change in characteristics at each image height, so lateral aberration is "insignificant," but it is extremely well corrected.

This is the reason why three aspherical lenses are used.

Spot Diagram

Spot Scale 0.3 (Standard)

As you can see in the lateral aberration, both sagittal and tangential aberrations seem to be well balanced and do not appear to have a V-shaped spot shape caused by sagittal flare, which is common in large aperture lenses.

Spot Scale 0.1 (Detail)

This figure shows a more enlarged view. The characteristics can finally be seen when the image is enlarged to show only the high performance.

There is a slight C-line (red) shift at the periphery of the image from 18mm to the outer edge of the image.

MTF

Maximum Aperture F1.4

Like the Art telephoto lenses we have analyzed so far, it has a high MTF from fno maximum aperture.

There is some image curvature at the 21mm focal length at the extreme periphery, but since it is at the corners of the image, it should not be a concern in shooting.

Small Aperture F4.0

MTF stopped down to fno4.0. Image curvature is not improved, but the resolution performance of the photo itself is further improved because the height of the mountains is increased.

Conclusion

As one would expect from the latest Art wide-angle lenses, they are extremely high-performance.

If you are in pursuit of performance and have permission from your "waist and knees," this is the lens for you.

I am looking forward to seeing what kind of pictures I can take when I combine the nostalgic 28mm angle of view with the highest performance.

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SIGMA 28mm F1.4 DG HSM Art

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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