This is a performance analysis and review article of the SIGMA Art 85mm F1.4 DG DN.
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 85 mm F1.4 DG DN is a large aperture medium telephoto single focus lens developed exclusively for full-size mirrorless in the high-performance and famous Art series.
First, let's review the definition of the product name of SIGMA, which I think is common sense.
SIGMA lenses are divided into three 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: 85 mm F1.4 "DG DN") are:
- DG (Full Size)
- DC (for APS / Four Thirds)
- HSM (Ultrasonic Motor)
- DN (Mirrorless only)
The product introduced in this article is the Art series 85 mm F1.4 "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 single-lens mirrorless camera by other companies using a mount adapter. However, it is necessary to note that this product is for mirrorless cameras only.
In addition, until now, SIGMA has sold products tailored to each company's lens mount, but as of this writing (2021), the DN series only supports Sony E Mount and L Mount jointly operated by SIGMA, PANASONIC and LEICA.
The 85 mm F1.4 lens of the Art series is the first lens for single-lens reflex cameras with mirrors released in 2016, and the mirrorless lens introduced in this article is the second.
In order to avoid confusion, I have listed them in the table below.
- Primary: 85 mm F1.4 DG HSM (2016) SLR
- Second generation: 85 mm F1.4 DG DN (2020) for mirrorless single lens
In the past, we have analyzed the first generation 85 mm, so please refer to the following link.
Also Read: SIGMA Art 85 mm F1.4 DG HSM (Original)
Private Memoirs
There is a reason for rushing this lens analysis of SIGMA this time.
The first generation Art85mm was released in 2016, and the second generation Art85mm in this article was released in 2020, which is a renewal after only 4 years.
Normally, the new product release cycle of camera lenses is 10 years at the shortest, and 30 years at the longest.
Even though this SIGMA Art85mm is for a mirrorless camera, it will be renewed after only four years, so I thought, "Didn't you find it to be a contraindication?" and decided that immediate analysis was urgently needed.
Also, in general terms, wide-angle lenses are more likely to benefit from the miniaturization and higher performance offered by a miller-less camera, and I wonder how effective a medium-telephoto lens like an 85 mm is.
However, it is hard to believe that the renewal of the medium telephoto lens will have a significant effect, so it must have evolved dramatically.
In the past, we introduced the case of Nikon, whose wide-angle zoom lens has evolved dramatically through the use of mirrorless technology.
Related Article: Comparison of new and old NIKKOR 14-24mm
With reference to this article, let's analyze the second generation Art 85 mm F1.4.
Document Survey
This time, we found that Japanese Unexamined Patent Application Publication No. JP2021-85935, which was registered as a new document at the time of the periodic survey, was the second generation 85 mm F1.4. Assuming that Example 7, whose shape closely resembles the configuration diagram of the official site, has been 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
Above is the optical path diagram of the SIGMA 85 mm F1.4 DG DN.
15 lenses in 11 groups, 1 aspherical lens effective in correcting field curvature and spherical aberrations in the lens closest to the image sensor, and 5 special low dispersion materials (SLD glass) effective in correcting chromatic aberrations (No. 2,3,4,6,9 lens) are also introduced.
Looking at the overall configuration, the first generation 85 mm F1.4 lens had a configuration like two Gaussian lenses, but the second generation 85 mm in this article has a configuration like one Gaussian lens with an increased number of components, and it seems to have come close to a symmetrical configuration.
Even if it is a medium telephoto lens, if you make effective use of the empty space on the image sensor side due to the mirrorless design, it will approach a symmetrical arrangement that makes it easy to correct aberrations, and it will be easy to realize miniaturization and high performance.
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 has the opposite characteristics to the full-correction type, which has a bulge on the negative side like an orthodox large aperture lens.
Spherical aberration is the basis of aberration and affects the overall appearance of the image. This inverse full-correction type spherical aberration shape is a common type in SIGMA's Art lenses. It is not only aimed at minimizing aberration, but also the shape is unified as a SIGMA-like taste.
Also Read: SIGMA Art 85 mm F1.4 DG HSM (Original)
Even in axial chromatic aberration, there is nothing to complain about.
Field Curvature
Field curvature is at a level that can be said to be "approximately zero" in accordance with the spherical aberrations.
Distortion
Distortion is a characteristic that is largely skewed to the plus side.
This type of graph shape is generally called a "spool shape", and in the state of the photograph, the periphery appears to be stretched.
The shape of this distortion is reproduced in the following simulation to make it easier to understand.
This graph reproduces the condition in which a grid pattern (grid pattern) like a calendar or a stone wall is shot.
The black line is the subject (ideal condition), and the red line is the condition of the photo taken with the lens.
Can you see the "pincushion shape" where the periphery is stretched by the distortion? This is the aberration shape called spool-shaped.
The amount of distortion on the plus side, which is so large, is unprecedented even in past analyses.
However, SIGMA explained this distortion in the product announcement video of the second generation 85 mm.
It explains that by intentionally leaving distortion aberration, miniaturization and high resolution have been realized.
Distortion aberration is an aberration that is easily corrected by image processing, so the correction was left to the camera and the development software.
Lateral Chromatic Aberration (Magnification Chromatic Aberration)
On the other hand, lateral chromatic aberrations is corrected to a minimum.
Since the deviation of the distortion aberration of each color of light becomes a lateral chromatic aberrations, I expected that it was left slightly large like the distortion, but it was dramatically reduced.
Transverse Aberrations
(Left)Tangential direction, (Right)Sagittal direction
Let's look at it as a transverse aberrations.
Considering the specifications of the 85 mm F1.4, it is surprisingly small.
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.
The spot diagram of the standard scale (± 0.3 mm) is almost the same from the center to the corner of the screen.
Spot Scale 0.1 (Detail)
After zooming in to the detail scale (± 0.1 mm), you can finally see the distorted shape at the corner of the screen, but the absolute value of the spot itself is small down to the corner.
MTF
Maximum Aperture F 1.4
Finally, let's look at the results of the MTF simulation.
The MTF is so high that it is difficult to distinguish which peak is the center performance line from the open Fno state.
When I saw the performance of the original Art 85 mm, I didn't expect to see a lens with more than this in the near future, but unfortunately I have to tell you that it has been updated after only four years.
Small Aperture F4.0
If you narrow it down to Fno4.0, you can't find a word other than to express it as "no aberration anymore".
Conclusion
I thought that a medium-telephoto lens could not be expected to have the effect of mirrorless, but it seems that by making it closer to a symmetrical arrangement, higher resolution and smaller size were realized at the same time.
Since this lens is also an optical system exclusively for digital cameras, it can be used for film.
By taking advantage of this advantage and leaving the distortion aberration on the plus side, it seems that the product was put together in the direction of accelerating the miniaturization effect.
This item shows the direction of the SIGMA Art series in the future.
If you actually look at the performance, the result is that SIGMA has evolved to an ultra-high performance that is suitable for renewal in just four years.
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.