PENTAX

The Ultimate Guide to the Comparison of OLD and NEW PENTAX FA 85mm F1.4 - Optical Design Value Analysis No.045

2023-04-29

This article compares and analyzes the performance of the new and old PENTAX FA 85mm 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.

Overview

Let's take a quick look at the history of the PENTAX 85 mm f / 1.4 lens.

The first lens appeared in 1984, but it was still the era of manual focus at that time.

Then, in 1992, the second generation lens, which was auto-focused and has long been referred to as a gem, appeared.

After that, the number was missing for 30 years, but the third generation lens was renewed in 2020 as a true hit of the digital age.

groups/elements

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

LEFT:The second 85 mm F. 1.4 (blue) , RIGHT:the third 85 mm F. 1.4 (red)

The above diagram shows the optical path of the PENTAX 85 mm f / 1.4 lens.

On the left is the second generation 85 mm F1.4, and on the right is the third generation 85 mm F1.4. Since the scale has been adjusted, the comparison is close to the actual size ratio.

As introduced in the individual analysis article, the second generation is a beautiful design that can be said to be the foundation of the modern large aperture monofocal lens with the rear group as the focusing group.

If you take a look at SIGMA Art lenses as a representative of modern lenses, I think you will be convinced.

Related article: SIGMA Art 85 mm F1.4 DG HSM

On the other hand, the third generation is a unique and unique lens with a sharp concave surface on the first lens, which is rare for a medium telephoto lens for SLR.

Longitudinal Aberration

LEFT:The second 85 mm F. 1.4 (blue) , RIGHT:the third 85 mm F. 1.4 (red)

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

In terms of spherical aberration, the second generation achieved more aberration correction than the manual focus lens while achieving auto-focus, but the full collection type spherical aberration has a bit of a flavor from a modern point of view.

With an open aperture, the image is soft and has a core inside, but when you narrow it down, the image quality is improved.

The third generation has increased the number of lenses and adopted aspherical lenses, so it can be said that there is no aberration, and the resolution performance is sharp from the open aperture.

Axial chromatic aberration depends on the number of lenses, so the number of lenses of the third generation is less than half of that of the second generation.

There is a 30-year gap between the launch dates of the new and old lenses. During this period, many glass materials have been developed. From the material point of view, we cannot overlook the fact that modern lenses are advantageous.

Field Curvature

Field curvature is greatly improved with the third generation lens as well as the spherical aberration.

Distortion

The third generation lens was also characterized by extremely low distortion, and the new lens that inherited this characteristic was also "zero."

Lateral Chromatic Aberration (Magnification Chromatic Aberration)

LEFT:The second 85 mm F. 1.4 (blue) , RIGHT:the third 85 mm F. 1.4 (red)

Lateral chromatic aberrations was also excellent with the second generation lens, so I think the degree of improvement with the third generation lens is small.

With the third generation lens, the difference between the g-line (blue) and the f-line (light blue) has been reduced, so it seems to be suitable for lateral chromatic aberrations correction by recent image processing. I guess they are doing it consciously.

Transverse Aberrations

LEFT:The second 85 mm F. 1.4 (blue) , RIGHT:the third 85 mm F. 1.4 (red)

(Left)Tangential direction, (Right)Sagittal direction

Let's look at it as lateral aberration.

If you look at the lateral aberration, you can see the high correction level of the third generation lens.

Since the number of lenses is large and aspherical lenses are also used, it is natural. However, even though the degree of freedom has increased, it is not easy to correct the aberration diagram to such a beautiful one because of the advanced technology.

It has a really high level of correction.

Spot Diagram

LEFT:The second 85 mm F. 1.4 (blue) , RIGHT:the third 85 mm F. 1.4 (red)

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.

If you look at the spot diagram on a standard scale, the third generation lens is really a "point" level.

The second generation lens has a large aperture, yet its round spot shape gives the impression of soft blur.

I have a feeling that I can't bear to separate the two.

Spot Scale 0.1 (Detail)

MTF

LEFT:The second 85 mm F. 1.4 (blue) , RIGHT:the third 85 mm F. 1.4 (red)

Maximum Aperture F 1.4

Finally, let's look at the results of the MTF simulation.

As you can imagine from the aberration diagram, the MTF of the new lens is extremely high.

The exquisite balance of the second generation lens can be said to be the work of the legendary designer. This is the real pleasure of enjoying the lens.

Small Aperture F4.0

Conclusion

Now, did you enjoy the PENTAX85mm F1.4 which has been renewed for the first time in about 30 years?

The evolution of optical systems is different from that of electrical components, and it takes a tremendous amount of time, but I think we were able to get a glimpse of the progress we have made over the past 30 years.

At the end of the day, there is no end to the question of whether to enjoy the exquisite and tasteful lenses created by the legendary optical designers or to enjoy the latest designs without compromise.

Sample Picture

Please refer to the analysis page of each lens for sample photos.

If you are looking for analysis information on other lenses, please refer to the table of contents page here.

Analyzed LENS List "HERE"

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