This is a performance analysis and review article of the MINOLTA AF 85mm F1.4 Limited.
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
In the previous article, I analyzed MINOLTA's AF85mm (first generation 85), and in this research, I found out the existence of 85 mm F1.4 Limited (Limited85).
It is a lens that was produced only 700 pieces in the world, but I thought it was using the same optical system as the first 85, but surprisingly, the optical system inside was specially designed.
Generally, the limited model lenses are mostly related to the design of the appearance. For example, the color is different or there is a carved seal. It is such a difference.
Even if we say that the optical system is different, it is only a matter of "changing the coating", and a cynical person like me can't help suspecting that "it must be fooling amateurs.".
However, when I looked it up, I found several articles from major media saying "It was designed around the same time as the first 85 mm, but it was in storage".
It seems that only 700 original lenses, which are really different from the optical design, were produced.
In the modern era, MINOLTA withdrew from the camera business, but when the α -7000 was released, which was the first in the world to adopt full-scale auto focus, it was a major manufacturer competing for first and second place in the industry.
It's hard to imagine such a big company developing and producing a lens that only produces 700.
First of all, let's check the genealogy of MINOLTA's α mount lens 85 mm f / 1.4 lens again.
Below is a list of the year of release and the number of lenses.
- AF 85mm F1.4(1987) 6/7
- AF 85mm F1.4G(1993) 6/7
- AF 85mm F1.4G(D)(2000) 6/7
- AF 85mm F1.4G(D)Limited(2001) 6/7This article
- search SONY Planar T* 85mm F1.4 ZA (2006) 6/8
*groups/elements
The first AF85mm F1.4 (unmarked) was released in 1987, and the optical system continued to be used until the third 85 mm F1.4G (D) model appeared in 2001. It seems that it continued to be produced until around 2006 when the MINOLTA lens died out.
In 2001, AF85mm F1.4 G (D) Limited, the phantom lens mentioned in this section, was introduced.
Private Memoirs
A few years after the release of this lens in 2001, MINOLTA transferred the camera business to search SONY and withdrew, so unfortunately there is no official site like "MINOLTA Camera History" now.
However, if it is around 2001, it is the beginning of the Internet, but it is an era when corporate sites and media sites have increased a lot.
After a thorough search for any remaining information on the Internet, we found that a portion of the official MINOLTA site was preserved from the so-called web archive site, from which we found an interview with a developer at the time.
Archive of interviews at the time
According to the interview article, "It was designed around the same time as the first 85 mm F1.4 around 1985. While minimizing spherical aberration, it left a small amount of aberration to improve the blur, achieving both high resolution and blur."
The original 85 and Limited85 were produced around the same time, and it was stated that "Limited85 was highly evaluated by the people concerned." However, the reason was not stated clearly, but as a result, it was shelved.
And after about 15 years, it has been revived with only 700 pieces.
The article also mentioned spherical aberration and lens cross-section as part of the design values, but unfortunately the images are missing from the archive.
Now, let's explore the real meaning of this lens by analyzing the design values.
Document Survey
If you look at the patent of the time slightly before the sale of the first 85 mm, it is true that two similar looking 85 mm have been applied.
Looking at the difference between the product release date and the application date, and the atmosphere of the performance described, it seems that JP-A-Sho 63-205625 is the prototype of Limited85.
Since the Limited85, which was actually revived and released, was released in 2001, there is a possibility that it has been refined with the latest glass materials, etc. However, in view of the interview articles at that time, etc., it is assumed that a product that is fairly close to the patent discovered this time has been commercialized, and the design data is reproduced below.
In addition, Example 2 was adopted because Example 1 resulted in an abnormal characteristic for some reason. There is no big difference in appearance between them.
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 diagram shows the optical path of the MINOLTA AF 85 mm F / 1.4 Limited.
It is composed of 7 lenses in 6 groups, and does not use special lenses or aspherical lenses.
Roughly speaking, it has the same structure as the first 85 mm.
However, if you look closely, the third lens (concave lens) is quite thick, and the aperture of the image side group is larger than the stop as a whole. Judging from the cross section, it is presumed that this Limited85 is heavy.
Referring to the product weight from the catalog, the 85 mm G (D) lens of the same optical system as the first 85 is 560g, and the product weight of Limited85 is 755g in the archive mentioned above, so it seems to be about 200g heavier.
The first 85 mm was released before the adoption of the SSM (ultrasonic motor), so it is presumed that auto focus was not possible with such a heavy weight.
Isn't this one of the reasons why it was put in storage for its high reputation of performance?
Longitudinal Aberration
Graphs of spherical aberration, image surface curvature, and distortion
Spherical Aberration , Axial Chromatic Aberration
Now let's look at what happens to spherical aberration, which the developers themselves say is distinctive.
It is certainly a strange aberration shape that does not seem to be the same optical type (double gauss) as the first 85.
A typical double Gauss has a shape called a full collection type in which the spherical aberration bulges to the minus side (left) at the middle part and becomes zero at the upper end.
A sense of resolution can be secured in the open. The main reason is that it is easy to balance with the fluctuation of the field curvature when narrowing down.
According to an interview with a developer, he said, "If you make it a full-collection type, it will be so-called two line blur, and it will be a factor that makes the blur look loud." On the other hand, if the spherical aberration is simply too small, it is expressed as "tasteless."
It is said that this is the ideal shape of the spherical aberration that enhances the resolution while leaving the soft blur.
Field Curvature
If the spherical aberration is a full correction type, the field curvature should be tilted slightly to the minus (left) side to improve the balance.
However, since this lens has a small spherical aberration, the field curvature is also close to zero.
It's not easy to get to zero, so it's also meant to make the spherical aberration a full correction type.
Distortion
The distortion is quite large for a medium telephoto lens.
In general, as the focal distance increases, distortion occurs on the plus side (spool-shaped), but a slightly larger amount of aberration remains on the minus side (cask-shaped).
It is not at a level that can not be used because it is often a numerical value in the zoom, but it may be different from the single focus of other medium telephoto.
Lateral Chromatic Aberration (Magnification Chromatic Aberration)
The lateral chromatic aberrations has been properly corrected. Considering the specifications of the large diameter and the small number of components, it can be said that it is an ideal condition.
Transverse Aberrations
(Left)Tangential direction, (Right)Sagittal direction
Let's look at it as lateral aberration.
In the tangential direction, coma aberration begins to stand out from around the middle image height of 12 mm, but there is little sagittal coma flare, so it can be seen that it is quite different from the previous double Gauss type.
In general, the halo (tilt) component of a double Gauss is in the same direction from the center to the periphery, but this lens is in the opposite direction from the middle image height. I can't get a clear picture of the overall performance until I see the movement with the MTF.
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.
The g line (blue) seems to stand out a little, but I think it doesn't bother you unless it's a very bad scene because the visibility is low.
Spot Scale 0.1 (Detail)
Except for the g-line (blue), everything is pretty well organized, so there should be no problem with the resolution.
As explained at the beginning, this lens was patented in 1985 and the product was released in 2001, so it is more likely that the design value has been refined.
In actual products, the introduction of the latest materials may further improve the chromatic aberration.
MTF
Maximum Aperture F 1.4
Finally, let's look at the results of the MTF simulation.
The MTF from the center to 12 mm in the middle is much higher than that of the first 85.
I can understand why the live action was highly evaluated.
In the actual shooting, the main subject is not included in the peripheral area, so the performance of the peripheral area is not added to the evaluation.
On the other hand, magazine companies and so on frequently evaluate the periphery which is easy to understand the difference.
For this reason, it was decided that a lens with such strong characteristics would not be accepted, and this lens may have been stored.
Small Aperture F4.0
The center has an extremely high resolution, and the Limite85, which suppresses the 2-line blur and improves the blur, is a premium lens with rare depiction characteristics even today.
Although it has not been officially mentioned, I would like to give you my personal opinion on the reason why this lens was put on the shelf.
Conclusion
I would like to enjoy the legendary lens which is full of resolution and blur.
It is difficult to obtain, but.
I would like to write articles on comparative analysis in the future.
- Weight that was difficult with AF technology at the time
- Distortion is large for the middle telephoto.
- It is characterized by the flatness of the MTF at the released Fno, and it is likely to be criticized in magazines along with distortion.
And other factors.
Regarding flatness, if you are concerned about it, you can improve it by narrowing it down by one step, and distortion can be freely corrected by electronic correction these days, so it will rarely be a problem in practical use.
I would like to enjoy the legendary lens which is full of resolution and blur.
It is difficult to obtain, but.
I would like to write articles on comparative analysis in the future.
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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.