This is a performance analysis and review article of the MINOLTA AF 35mm F1.4.
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.
MINOLTA AF 35 mm F1.4 is a large aperture wide angle lens developed for the world's first full-fledged autofocus compatible SLR.
The world's first full-scale autofocus SLR α -7000 was released in 1985, and the AF 35 mm F1.4 of this article was released two years later in 1987, which shows that it was prepared from the early stage of system development.
Surprisingly, even after MINOLTA sold the camera business to SONY, part of the optical system of this AF 35 mm F1.4 lens was improved and reused. It is a long-selling design that continues to be sold as "SONY SAL35mm F1.4G" in 2021 (as of writing).
By the way, the 35 mm f / 1.4 lens is considered to be the representative "face" of each company in modern times (2021), but this is a story from the 2000s.
A long time ago, the 35 mm f / 1.4 specification lens was rather a special specification, rather than one that many manufacturers sell.
Looking back at the film era prior to 2000, NIKON released a 35 mm f / 1.8 lens with manual focus from 1971, when the F mount was first launched. MINOLTA's 35 mm f / 1.4 was the brightest Fno product.
Although MINOLTA was the first company to offer autofocus support with the 35 mm f / 1.4 specification, other companies were only able to offer autofocus support around the end of the 90s, more than a decade later.
As I introduced a little in the article of MINOLTA AF 28 mm F2.0 analyzed in the past, the lens of this article was evaluated as follows in the book "Interchangeable Lens' 94" edition by the late Professor Hideo Nishidaira whom I respect as a demon of the lens evaluation.
A wide-angle lens with the largest aperture among autofocus lenses, with extremely stable image quality from the opening to the periphery and high uniformity
Citation CAPA Responsibility Editor Interchangeable Lens' 94 by Hideo Nishidaira
It is fair to say that the highest level of praise has been given.
However, when SONY reused this optical system and resold it as "SONY SAL35mm f / 1.4G" in 2006, it was severely criticized by famous evaluation sites overseas for large chromatic aberration.
It is natural that the evaluation differs because there is a big gap between the time around 90 when the MINOLTA version was released and the time in 2006 when the SONY version was released. Professor Nishidaira's comment also states that "the center does not reach 35 mm f / 2.0", and it can be seen that the evaluation content respects that it is the only f / 1.4 autofocus lens at that time.
Therefore, we will analyze the performance of the 35 mm f / 1.4 lens starting from this MINOLTA AF lens. In addition, by comparing each company including SONY, we should be able to obtain an analysis result that can be said to be a reconfirmation of the trend of modern large diameter lenses. From this time, we will continuously deliver analysis articles of the 35 mm f / 1.4 lens continuing from MINOLTA to SONY.
First of all, let's look back on the lineage of lenses from MINOLTA to SONY.
A large 35 mm aperture in MINOLTA's SLR lenses starts with the F1.8, and from the transition to the autofocus system comes the F1.4 large-aperture lens.
After that, the business was sold to SONY, and 2 F1.4 lenses appeared, and I will arrange them in order of release year.
- 1987 MINOLTA AF 35 mm F1.4
- 2006 SONY SAL35mm F1.4G (MINOLTA)
- 2015 SONY Distagon T*FE 35 mm F1.4 ZA
- 2021 Sony 35 mm f / 1.4 gm
In detail, (1) it seems that there are 3 types of MINOLTA lens, G and New.
According to one theory, these three species are rumored to have changed a part of the design, but as far as I see the composition diagram, they all look the same.
Therefore, if you check the wording of the literature and catalogs at hand, you can see that there is a difference in aspherical lenses.
It states that the initial lens is a ground aspherical lens, and G and New are glass mold lenses.
At MINOLTA, the ground aspherical lens was called a "generating aspherical lens."
This grinding aspherical lens is to grind an aspherical lens by pressing a grinding stone against the glass surface while rotating the glass with a thing like a potter's wheel.
On the other hand, a glass mold is a process that high-pressure presses glass in an ultra-high-temperature mold and finishes it into a lens shape. It can be thought of as an ultra-high-precision version of plastic model parts processing.
Because the MINOLTA AF 35 mm F1.4 is a unique long seller, the processing method of the aspherical lens has changed in the long term production.
At this time, it is assumed that some designs were modified for glass molds because the processing method limits the glass materials that can be used and the degree of freedom of shape.
Another problem with products that have been manufactured for a long time in this era is the need to switch to lead-free glass.
Around 2000, the glass materials industry began switching to lead-free materials, which are environmentally friendly.
As a result, the optical properties of some glass materials have been altered, and some glass materials have been discarded. As a result, many products have been forced to change some of their design values.
It is assumed that such changes in the processing method and switching of materials were not usually explained in detail to the user side, but were vaguely announced as "partial improvement", and the model number (model name, etc.) was often changed due to the convenience of manufacturing management.
This kind of behind-the-scenes information on the manufacturer side has leaked out a little in magazine articles and interviews, and only the records (memories) of the situation where it is not clear whether it is a rumor or the truth remain.
At that time, the Internet was not widely used, so it was difficult to verify and confirm.
I think this "rumor" is not completely wrong, and there is a good possibility that the performance was changed to the extent of seasoning at the same time as changing the processing method and materials.
However, in this blog, we treat MINOLTA AF to SONY SAL as the same item because the number of composition is the same and there is no extreme difference.
According to a search of patent documents, JP6361213 which was published at the time of the launch of the first generation lens, has the same shape and specifications as the MINOLTA AF 35 mm F1.4. According to the configuration diagram of the embodiment, since Embodiment 2 closely resembles the shape of the product, assuming that it was commercialized, the design data will be reproduced below.
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 MINOLTA AF 35 mm f / 1.4.
Composed of eight groups and ten lenses, the ninth lens uses one aspherical lens.
The overall configuration is called retrofocus, consisting of a rear group of double Gaussian-type lenses centered on the aperture and a front group of concave lenses arranged on the object side. This is a level of composition that you would want to see beautifully in a textbook.
Even if you look at the SIGMA 35 mm F1.4 Art released later, it is clear that it follows this flow of composition.
Also Read: SIGMA 35 mm F1.4 DG HSM Art
The "double floating mechanism" is used for focusing.
Before we get into what a double-floating mechanism is, let's take a quick look at some common lens focusing methods.
In the era of manual focusing, many lenses used a method called the "full-group advancing method," in which the entire lens is moved toward the subject to focus.
This full-group feeding method has several problems. Typical problems include "performance deterioration in short-distance shooting" and "heavy moving lens".
This led to the creation of a method called floating focus, in which the lens group is divided into two and the two lens groups are moved by different amounts.
Now, the lens in this article uses a "double" floating mechanism, so it's even more complicated.
Let me illustrate it there.
The above figure is a schematic diagram of the double floating system.
According to the patent document of MINOLTA AF 35 mm F1.4 in this article, the whole is divided into three blocks as shown in the above figure. Block A is fixed (FIX) when focusing, and block B and block C move independently to focus.
With such a complex focus structure, it is possible to achieve high-speed autofocus by eliminating the need to move the A block while preventing performance degradation.
Graphs of spherical aberration, image surface curvature, and distortion
Let's start with the spherical aberration. It is a way of putting together a full-collection type that bulges to the minus side, which is unique to old lenses. In open Fno, it will be a rather tasteful and soft description.
Axial chromatic aberration also has a fairly large value.
It can't be helped because the special low dispersion material which is effective for chromatic aberration is not used.
As a similar case analyzed in the past, is Zuiko 35 mm F2.0 close in atmosphere?
Also Read: OLYMPUS Zuiko 35 mm F2.0
Also, as a representative example of modern design, if you look at the SIGMA Art 35 mm F1.4, can you feel the history of the development of modern lenses?
The field curvature is well compensated up to a height of about 18 mm at the edge of the screen, but it fluctuates sharply toward a height of 21 mm at the corner of the screen.
The distortion is a cask-shaped aberration that falls to the minus side because of the wide-angle lens, but in absolute terms, it is at an excellent level.
Lateral Chromatic Aberration (Magnification Chromatic Aberration)
The lateral chromatic aberrations is also well compensated up to a height of 18 mm around the edge of the screen, but the g line (blue) strongly fluctuates toward a height of 21 mm at the corner of the screen.
However, I think that it is sufficient for practical use because it is only g line (blue) with low visibility.
(Left)Tangential direction, (Right)Sagittal direction
Let's look at it as Transverse Aberrations.
Because of the large aperture, the coma flare in the sagittal direction is enormous.
Spot Scale 0.3 (Standard)
This is the result of an optical simulation, but first let's look at the spot diagram.
The spot shape has a large diameter, but the shape is not an unpleasant shape, so I think I can enjoy a soft description.
Spot Scale 0.1 (Detail)
Maximum Aperture F 1.4
Finally, let's look at the results of the MTF simulation.
The open MTF is quite low, and if you look for a similar example from past analysis, the peak is a little lower than the OLYMPUS Zuiko 50 mm f / 1.2.
In terms of the degree of coincidence at the top of the mountain, it seems to be moderate except for the statue height of 20 mm at the corner.
Small Aperture F4.0
If you narrow it down to F4.0, you can get enough resolution.
It's pretty bold, and you can see why the 35 mm f / 1.4 hasn't been touched.
The reason is simple. A SLR needs to be designed with a long back focus, which is the distance from the lens to the image pickup device, so a wide-angle lens has that limitation.
Moreover, it is a large aperture of F1.4, so it is extremely difficult to design in the first place.
At around 35 mm of focal length, it becomes hard to secure the back focus, which is the reason why 35 mm is always slightly inferior to 50 mm.
In the future, I would like to compare and analyze the performance of various lenses with the same specifications, starting with the MINOLTA 35 mm F1.4 lens, which is the world's first autofocus compatible lens.
This article is part of a series analyzing the history of the 35 mm f / 1.4 lens from MINOLTA to SONY.
Example photos are in preparation.
If you are looking for analysis information on other lenses, please refer to the table of contents page here.