SIGMA

Optical Design value Analysis - SIGMA 135mm F1.8 DG HSM Art [No.011]

2022-04-06

This is a performance analysis and review article of the Sigma Art 135mm F1.8.

We analyze the lens performance through simulation by inferring the design values of the optical system from patent information and actual photographic examples.

Professional lens designer Jin Takayama carefully unravels design information such as optical path diagrams and aberration characteristics, which are rarely seen by the general public, and provides a deep and gentle explanation of the lens' flavor and descriptive performance.

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

Overview

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

The 135mm F1.8 DG HSM Art lens introduced in this section is a large-aperture medium telephoto lens that boasts extremely high resolution performance.

This lens has the longest focal length among Sigma's Art single focal length series. (As of writing in 2020)

Currently, the Fno. of the Art single focal length series is basically F1.4, but only this lens has F1.8.

The longer the focal length of a large-aperture lens, the larger the lens diameter (thickness), and the greater the impact on weight.

The focal length of a large-aperture lens increases with the diameter (thickness), and the effect on the weight is even greater.

The 105mm F1.4 lens weighs 1.6Kg with a tripod mount, while the 135mm F1.8 weighs about 1.2Kg, a difference of 400g, which is a significant advantage.

Private Memoirs

For me, the 135mm focal length is the focal length of the first telephoto lens I ever used, so I am deeply attached to this specification.

However, in today's age of telephoto zoom lenses, I wonder if it is a half-baked specification, or if there have been few ambitious new products in recent years…

I would like to see new products from manufacturers other than SIGMA.

Until the 1960s, the majority of cameras were rangefinder cameras, such as the Leica, but these rangefinder cameras had a separate optical system for the viewfinder and the shooting lens, making it very difficult to shoot with a telephoto lens.

Therefore, the focal length of 135mm was the longest focal length for rangefinder cameras in actual use.

After that, when the problem of telephoto photography was solved with the advent of SLR cameras, telephoto lenses were developed one after another from 200mm to 400mm to 600mm, as you probably know.

Therefore, the 135mm focal length became a modest focal length specification, and I believe that it is a nostalgic specification in the modern age.

Continuing from the article on the SIGMA 35mm F1.4 Art, I will now 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.

Starting with a focal length of 35mm, we have been analyzing the longer focal lengths in random order, and now we are finally at the end of the longer end of the spectrum.

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SIGMA 135mm F1.8 DG HSM Art

Document Survey

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

Unfortunately, there is no data for a cross-sectional drawing that exactly matches the product drawing published on the website.

However, since the basic configuration of Example 4 of Patent Publication 2017-173409 is almost identical, I will assume that this is the design value and reproduce the design data below.

The biggest difference between the product and the patented data is that the patented data shows a three-piece bonded lens on the image side of the aperture, while the product shows two-piece bonding and separation into a single lens.

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 135 F1.8.

The lens has 13 elements in 9 groups, and although it does not appear to employ aspherical lenses, it also has 4 elements of special low-dispersion material for good correction of chromatic aberration.

Compared to the SIGMA 105mm F1.4 we analyzed in the previous issue, the number of elements is smaller, so the appearance of a slightly luxurious medium telephoto is not so strange.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

Looking at the spherical aberration, it seems to be beautifully corrected to the same level as the SIGMA 100mm F1.4, even though the Fno is set to 1.8.

Image Surface Curvature

The image curvature is a slight tangential and sagittal deviation at the highest periphery of the image, but this is at the corners of the image, so the effect on the photograph will be negligible.

Distortion

Distortion is only slightly threadbare because it is a telephoto system, but in absolute terms it is not at a level that affects the photograph.

Chromatic Aberration

Magnification chromatic aberration is fairly ideally corrected.

The F line (light blue) and the c line (red) are extremely small, and the g line (blue) remains slightly. The g line, which has low visual sensitivity, does not affect the image so much that you will not notice any chromatic aberration in actual shooting.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Sagittal aberration is very small, which seems to be largely due to the effect of keeping the Fno at 1.8.

Tangential halos remain, but my reproduction data may be somewhat inadequate. Maybe I should have made the front element a little smaller.

The reason for this is that the lens patent does not list the aperture data of the lens, so it must be entered by prediction, and if this prediction is not accurate, the halo and coma in the lateral aberration will easily increase.

Spot Diagram

Spot Scale 0.3 (Standard)

Tangential spots are a bit scattered, but the density is low, so it does not seem to be a problem.

Spot Scale 0.1 (Detail)

The level of detail can be seen only when the image is zoomed in.

MTF

Maximum Aperture F1.4

At fno1.8 maximum aperture, there is a curvature component from the mid-image height, and the tops of the mountains are slightly off.

However, this is at a high enough level so it does not seem to affect the actual image.

Small Aperture F4.0

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

It is as high performance as the Art 105mm F1.4, but I am rather afraid of myself who has become accustomed to such performance as if it were a matter of course.

I may have been infected with some kind of luxury disease.

This lens is compact among the Art lenses, and the unique angle of view of 135mm is hard to throw away, so I have no end of worries about whether I should buy it or not.

Conclusion

The SIGMA Art 135 1.8, the longest SIGMA Art single focal length, proved to be an extremely high-performance lens that did not disappoint.

It has a high MTF that will make your eyes sparkle, low chromatic aberration that will make you sigh, and to top it off, unlike other Art lenses, this lens does not use an aspherical lens, so you can expect a beautiful, straightforward bokeh effect.

I can't help but try this lens that satisfies all the elements.

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SIGMA 135mm F1.8 DG HSM Art

Sample Picture

Example photos are under construction.

If you are looking for analysis information on other lenses, please refer to the table of contents page here.

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