This is a performance analysis and review article of the SONY FE 85mm F1.4 GM
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
The SONY FE 85 mm F1.4 gm is the best large-aperture mid-telephoto lens in the SONY FE lens series (as of 2020).
The "GM" at the end of the 85 mm name is an abbreviation for "G Master," which is above the "G" designation for high-grade lenses from the A (α) mount era of MINOLTA.
The point is that GM is "the best MINOLTA lens."
On the other hand, the 50 mm F1.4 has the grade name of ZEISS which has been used by SONY for a long time, and is "the highest grade of SONY lenses".
It is a very interesting question as to what kind of difference there is in the optical design between the two.
The 85 mm F1.4 in this section is a GM = MINOLTA-based lens, so let's start with the A (α) mount of the MINOLTA 85 mm F1.4.
- AF85mmF1.4(1987)6/7
- AF85mmF1.4G(1993)6/7
- AF85mmF1.4G(D)(2000)6/7
- AF85mmF1.4G(D)Limited(2001)6/7
- SONY Planar T* 85mm F1.4 ZA (2006)6/8
- SONY FE 85mm F1.4 GM(2016)8/11
This is a new system A (α) mount of MINOLTA, which was developed on the premise of auto focus starting from 1985. The first AF85mm F1.4 (unmarked) will be released in 1987, two years after the start.
In 1993, the second generation lens was promoted to "G-grade" with the same optical system but equipped with an SSM (ultrasonic motor).
Furthermore, it is presumed that the optical system is the same until the 3rd lens G (D) in 2000, but the 4th Limited in 2001 is a limited lens that was produced only 700, but "the optical system is surprisingly different".
It's quite an interesting story, so I'd like to follow up on it.
I added it to the list at the end, but there are also A (α) mount lenses made by SONY, and they are named Planar T * and ZEISS, but this seems to be a mysterious lens in various ways.
The "SONY FE85mm F1.4 gm" mentioned in this section was born in 2016 as a full-size large aperture medium telephoto E-mount for mirrorless cameras, which was developed after MINOLTA merged with SONY.
Private Memoirs
The year 2016, when this lens was released, was probably the lucky year of 85 mm.
The "85 mm F1.4 dg HSM" of the SIGMA Art series and the "SONY FE 85 mm F1.4 gm" of this item are released at the same time.
The SIGMA Art series is an easy-to-understand top-of-the-line series aimed at ultra-high performance. On the other hand, the SONY 85 mm GM is definitely in the upper class, although I am not sure which is higher than the ZEISS.
An interesting comparison of the two will be summarized in a separate article. First, let's analyze the SONY 85 mm in depth.
Document Survey
The document appears to be WO2017/130571. From this, it is assumed that Example 1 whose shape looks similar is commercialized, and the design data is reproduced as follows.
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 SONY FE 85 mm F1.4 gm.
It is equipped with 11 lenses in eight groups, one aspherical lens to greatly improve resolution, and three special low dispersion lenses (ED) to reduce chromatic aberration.
Since the angle of view is different, direct comparison is not possible, but the FE 50 mm F1.4 za, which is a SONY ZEISS brand, is an ultra-high-performance and unique optical system that has evolved like a dinosaur, whereas the 85 mm GM is a relatively orthodox medium telephoto lens with a specially processed aspherical lens.
This special aspherical lens is called Ultra-High Aspherical XA. According to the explanation on the official website, the surface is very smooth, and there is little adverse effect on the blurring caused by the aspherical lens, and it seems to keep the beauty.
When a large diameter lens is equipped with an aspherical lens, the phenomenon called onion ring blur or annual ring blur becomes noticeable, but SONY has found a solution.
The difference from the orthodox mid-telephoto lens is that, as is the case with mirrorless cameras, the whole area near the image pickup device is completely covered with glass.
I thought that the advantage of the mirrorless would be small when it comes to the middle telephoto lens because there is a margin in the back focus (the distance from the lens to the image pickup device), but it seems that it has been completely used up.
Let's take a look at the performance in order.
Longitudinal Aberration
Graphs of spherical aberration, image surface curvature, and distortion
Spherical Aberration , Axial Chromatic Aberration
The spherical aberration seems to be corrected sufficiently. The area where the c line (red) and the f line (light blue) overlap at the top of the graph also seems to have a high sense of resolution and can be said to be a good impression.
G-line (blue) at top edge It is slightly shifted to the plus side, but the aberration can be cut if it is reduced by 1/3 stage, and with this amount, it is not open or noticeable.
Axial chromatic aberration is also a sufficiently small area. This is probably the reason why we have introduced a large number of special low-grade materials.
Field Curvature
The field curvature has been corrected to be almost flat.
Distortion
The distortion remains slightly positive, but it is not noticeable.
Lateral Chromatic Aberration (Magnification Chromatic Aberration)
The lateral chromatic aberrations is not so small, but it is easy to correct the lateral chromatic aberrations by image processing in a digital camera, so it may be balanced with the post-processing side because SONY is considered to be strong in image processing.
Transverse Aberrations
(Left)Tangential direction, (Right)Sagittal direction
Let's look at it as transverse aberrations.
The coma aberration (asymmetric component) in the tangential direction is quite minimal, and you can feel the high resolution.
On the sagittal side, the coma flare remains a little, but it is a sufficient level for an F1.4. Since the peripheral part of the opening is slightly blurred, I think there are many people who prefer this level as a portrait lens.
If you narrow it by one step, it will be improved enough and high resolution will be obtained.
Spot Diagram
Spot Scale 0.3 (Standard)
The results of the optical simulation will be shown from here, but let's look at the spot diagram first.
As you can see in the vertical aberration, the g-line (blue) remains slightly in the center of the screen, but the blue is not a noticeable level because the visibility is low.
A small amount of sagittal coma flare remains, but there is no strong V-shaped feel even when looking at the 18 mm image height around the periphery.
Spot Scale 0.1 (Detail)
This spot scale of ± 0.1 is the same simulation as ± 0.3 (standard), but the scale has been changed to enlarge the spot diagram, because it is difficult to see with a high-performance lens on the standard scale.
MTF
Maximum Aperture F1.4
Finally, let's look at the results of the MTF simulation.
As expected, it is a large aperture of F1.4 like a modern lens, but the peak is high from the open Fno, and the deviation of the position seems to be small, and you can see that it is a high resolution with sharp from the opening.
Small Aperture F4.0
From the open to the high performance, if you narrow it down to F4, it is almost the aberration free level performance.
Conclusion
I understand that it is naturally high performance because it is a G Master grade lens that SONY is proud of.
In addition, the fact that it is relatively light for a modern high-performance lens is also important from a practical point of view.
There are few examples of analysis, so I can't say for sure, but the ZEISS grade is focusing on performance, and the GM grade is focusing on a practical balance between performance and weight / size.
In addition, this was the first case of mid-telephoto as an analysis of a mirrorless lens, and surprisingly, it was found that the mid-telephoto lens was also designed to make use of its characteristics.
I am still interested in the comparison with the SIGAM Art 85 mm that was released at the same time, but I will analyze this comparison in a separate article in the future.
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.