This is a performance analysis and review article of the SIGMA 35mm F1.2 DG DN Art.
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 35 mm f / 1.2 is an ultra-large aperture wide-angle monofocal lens developed exclusively for full-size mirrorless in the high-performance and renowned Art series.
First, let's review the definition of the product name of SIGMA, which I think is common sense.
The SIGMA lens is divided into 3 genres as a basic series.
- Art (high performance)
- Contemporary (balanced)
- Sports (high mobility)
For the explanation in (parentheses), I freely translated the explanation written on the official website in one word.
And the symbols at the end of the name (for example, 35 mm F1.2 "DG DN") are:
- DG (for Full-Frame Cameras)
- DC (for APS Size Camera / Four Thirds Camera)
- HSM (Hyper Sonic Motor)
- DN (for Mirrorless Cameras only)
The product introduced in this article is the Art series 35 mm f / 1.2 "DG DN", so it is "full-size" and "mirrorless only".
If the product was designed for a conventional single-lens reflex camera with a mirror, the lens could be used for a mirrorless single lens using a mount adapter. However, it is necessary to note that this product is for mirrorless use only.
Also, SIGMA sells products tailored to each company's lens mount, but as of this writing (2021), the DN series is only compatible with the Sony E mount.
Private Memoirs
For a long time, from 1970, when single-lens reflex cameras were in their prime, to around 2020, a 35 mm lens was a sad and unfortunate focal length.
In a single-lens reflex camera, a quick return mirror is placed between the lens and the image sensor to guide the light to the viewfinder. The distance between the lens and the image sensor is called the back focus.
A lens with a focal length of 35 mm is sometimes treated as a 50 mm lens and a "standard lens" together, but it is difficult to take a long back focus because of the slightly wide angle, and it has been difficult to improve the performance for single-lens reflex cameras with mirrors.
Therefore, in order to ensure sufficient performance, the product becomes larger, so compared to 50 mm lenses, many 35 mm lenses have a slightly darker Fno.
(SIGMA's Art series was famous for ignoring the size.)
As for the "angle of view" of the standard lens, the 35 mm lens, which is close to the natural field of view of the human eye, seems to be less strange, but the 50 mm lens, which can be made into a symmetrical configuration, is small, cheap, high-performance, and has a bright Fno, so it has never given up the position of standard & royal road.
As a result, although the 35 mm lens is said to be the standard, it has not been able to reach 50 mm, and has spent 50 years full of sorrow and suffering.
(There is a definition of a standard lens. The above is an author's assumption.)
After 2020, mirrorless single-lens cameras became the mainstream.
Mirrorless cameras enable optical designs with a short back focus.
If that's the case, then maybe 35 mm will become the standard in the true sense of the word, ushering in a golden age.
Document Survey
Now, since it is a super-large aperture single focus lens of F1.2, it does not require the level of work such as investigation, and it can be seen at a glance.
There is no doubt that it is Japanese Patent Application Laid-Open No. 2019-197125, but it seems that the number of configured sheets is slightly different, but assuming that Example 4 having a particularly similar configuration is commercialized, the design data of Example 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
Above is the optical path diagram of the SIGMA Art 35 mm f / 1.2.
The original configuration is 17 sheets in 12 groups, but in this patent example, it is 18 sheets in 12 groups, which is one sheet more. I am sure that the number of sheets was reduced as a result of detailed design for actual products.
If you remove the 4th lens in this cross-sectional view, it looks almost the same as the product lens.
We have introduced three SLD lenses to correct chromatic aberration and three aspherical lenses to correct spherical aberration and field curvature.
There are not many other products with 35 mm f / 1.2 specifications. If you look at the Zuiko 50 mm f / 1.2, which was designed about 40 years ago as a similar product analyzed in the past, you will see how modern lenses have high-dimensional correction.
Also Read: Zuiko 50 mm f / 1.2
Longitudinal Aberration
Graphs of spherical aberration, image surface curvature, and distortion
Spherical Aberration , Axial Chromatic Aberration
Let's look at the spherical aberration first.
This is an unmistakable straight line. When Fno is a bright lens, it means that a large amount of light enters the lens. When a large amount of light enters the lens, it becomes more difficult to form an image at one minimum point.
The amount of deviation that cannot be focused on one point is called "aberration." Although this lens has a super large aperture of f / 1.2, it is able to suppress aberrations to a minimum.
The axial chromatic aberration is as small as the spherical aberration. It is the effect of introducing 3 SLD lenses.
Field Curvature
Field curvature is also put together in a small size.
Distortion
Distortion occurs to about -5% at the corner of the screen at an image height of 21 mm, and is barrel-shaped.
At the wide-angle end of an inexpensive zoom lens, this amount may remain, but since the distortion aberration of a normal SIGMA Art lens is about zero, a considerably large amount remains.
The reason for this is stated on the official website, but it explains that distortion and vignetting are corrected by image processing on the camera side.
Unlike optical finders and film cameras, mirrorless single-lens cameras always have the opportunity to see only images that have undergone image processing, so they process the parts that are suitable for digital processing and perform new-age aberration correction that corrects other aberrations as much as possible.
Lateral Chromatic Aberration (Magnification Chromatic Aberration)
Lateral chromatic aberrations also left a slightly large g-line (blue), but it is assumed that this is also corrected by image processing.
Transverse Aberrations
(Left)Tangential direction, (Right)Sagittal direction
Let's look at it as a lateral aberration.
In terms of lateral aberration, the g-line (blue) has undergone aberration correction at a level that is hard to believe for a super-large aperture of f / 1.2, although it is slightly off because correction is assumed in image processing.
Spot Diagram
Spot Scale 0.3 (Standard)
Now let's look at the optical simulation results, but first let's look at the spot diagram.
At spot diagram, this is a "near point" concentration on a standard scale.
Spot Scale 0.1 (Detail)
If you look in detail, you can see how much of the g-line (blue) remains.
MTF
Maximum Aperture F1.2
Finally, let's look at the results of the MTF simulation.
The MTF is the coincidence of the impact height and position from the release Fno.
You can see that they are aiming for a completely "open-to-use" design.
Small Aperture F4.0
If you narrow down to f / 4.0, the MTF peaks at the periphery of the screen will be dramatically improved.
Conclusion
As SIGMA Art lens is the first F1.2 super-large aperture lens, I assumed that aberration correction of an optically abnormal level has been performed, but I understood well that a precise design considering the feeling of size has been performed by combining it with aberration correction by modern image processing.
For example, compared to the SIGMA Art 35 mm f / 1.4, which we analyzed again in terms of weight, this time the Fno is as bright as f / 1.2, but it has the same high performance as f / 1.4, but the weight is limited to an increase of about 300g.
Also Read: SIGMA Art 35 mm f / 1.4
If you are looking for a 35 mm lens with a large aperture and high performance, this is the best option.
I pray that this lens will save the sorrow of all 35 mm lenses and that the 35 mm golden age will come.
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.