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The Ultimate Guide to the RICOH GR3x 26mm F2.8 - Optical Design Value Analysis No.062

2024-01-04

This is a performance analysis and review article of the RICOH GR3x 26mm F2.8.

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

RICOH GR is the name of a series of traditional compact cameras that Ricoh is proud of. The GR3x is a third generation variant of the series, and is a special version with different lens specifications from the previous mainstream GR products.

In the past, the specifications of most GR series lenses were based on wide-angle lenses with a focal length equivalent to 28 mm when converted to full-size, and there were a few products with different specifications of 21 mm or 35 mm in the silver halide film era.

Since the optical system of this RICOH GR3x uses an APS-size sensor with a focal length of 26 mm Fno2.8, the focal length is equivalent to 40 mm in full-size terms, and this is the first focal length in the standard range in the GR series.

In our blog, we compare and analyze the past GR series lenses, so if you are interested, please refer to the following link as well.

ALSO READ: COMPARISON OF RICOH GR SERIES

Private Memoirs

The focal length of the RICOH GR3x to be analyzed in this article is 40 mm (full-size equivalent). "Why did you choose 40 mm?" This is an interesting choice.

Why is 50 mm the standard?

A standard lens generally has a focal length of 50 mm, but I think many people think 35 mm is more appropriate.

If you look at the debate between the 50 mm and 35 mm factions, peaceful lensists may think, "It would be better to make it about 40 mm in a quarrel."

First of all, the reason why the focal distance of 50 mm is regarded as the standard lens comes from the fact that 50 mm was adopted as the first Leica lens by Oskar Barnack, who created the Leica, the progenitor of the 135 film camera.

But here happened a very unfortunate situation that caused controversy, because there is no "reason to adopt a 50 mm lens" left.

For this reason, even though there have been several theories that "this is the reason why it was adopted," there has been no definitive answer, leading to the standard lens controversy that continues even today.

Here, if I guess the psychology of Kamewota and others, I would like to think that "50 mm was chosen as a standard as a result of technically advanced consideration", but the fact is that Mr. Oskar Barnack liked photography, so it is not strange that he simply "liked the angle of view of 50 mm".

Or, there is no denying the possibility that economic problems such as "50 mm was produced within the budget" are involved.

That's why the standard lens debate goes on forever.

Another famous anecdote is that the Leica 50 mm lens has an accurate focal length of 51.6 mm.

Again, there seems to be no reason left for the same 51.6 mm.

Therefore, there are many people who think that the 51.6 mm figure, which seems to be a half-measure, "has some deep intention, and 50 mm was decided as the standard," and they read it deeply, and the standard argument war deepens again by reading it deeply.

For me, who makes a living designing lenses, I feel that when I try to design a 50 mm lens, the only thing I can say is, "The 51.6 is the one with the best performance."

Diagonal theory

The exact derivation for the standard 50 mm has been lost, but the only theory with a numerical basis is that it "matches the diagonal length of the image sensor" (diagonal derivation theory).

The diagonal length of the so-called 35 mm plate film (135 film) is certainly close to 50 mm.

In addition, if the focal length that matches the diagonal length is used as the standard lens, a lens with the same specifications as the angle of view is selected whether it is full-size, medium-size, or large-size, and an intermediate focal length that is neither wide-angle nor telephoto is selected, so it has an atmosphere suitable for being called a standard.

However, there are some doubts to believe the theory of diagonal origin.

Please refer to the following figure, which shows the dimensions of the full-size sensor.

Did the GR3x pursue a true standard lens?

Now, the argument without an answer does not end here, but if you believe the diagonal origin theory, it can be said that the focal length of 40 mm is a "true standard lens".

The fact that a 40 mm (equivalent) lens has been mounted on the RICOH GR, which is a camera-integrated type with no lens replacement, is naturally the result of a strong awareness of the "true standard".

  • This is all arbitrary speculation.

Now, let's look specifically at the "performance of a true standard lens."

Document Survey

In my daily patent patrol, I was aware that RICOH had filed a suspicious patent application for a single-focus lens, but even I didn't realize that I had expected GR to adopt it.

The release of RICOH RG3x was announced, and at the same time, the configuration diagram of the lens is included in the information, so it was easily found out.

The related patent of RICOH RG3x is JP No. 2020-144271. Among them, Example 4 seems to be closer in appearance. Assuming that this is 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

Although this lens is an APS-C size lens, the scale of the graphs has been adjusted so that it can be easily compared with the full-size lens.

In terms of an image, the scale of the graph has been changed so that if it were expanded for a full-size sensor, it would be like this. As an optical system, it can be evaluated side by side.

As a note, there is no problem with this evaluation in terms of lens (optical), but as for the actual photograph, a camera with a small sensor is inferior to a large format in terms of noise and the number of pixels, so please note that that is not taken into account.

Optical Path Diagram

The above diagram shows the optical path of the RICOH GR3x 26 mm f / 2.8.

Composed of seven lenses in five groups, aspherical lenses are used for the first lens on the most object side and the seventh lens on the most image side.

Should I say that this form adds a convex lens to the subject side of GR3?

As we analyzed in the past, the optical system of GR3, which has been refined over many years, is close to the essence of lens design, and GR3x is an improved type based on this design.

Even if you understand the story, you can't help but wonder if this is actually possible.

I can understand why the part "GR3" was left as the name of the product.

GR40 should have been good, but there was a good reason to leave "3".

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

In terms of spherical aberration, when you think of a standard lens, you tend to think of it as a full-collection type lens that bulges in the minus direction. However, the GR3x lens corrects the aberration to a very small value, and predicts that it has a high resolution that is crisp from the opening.

The axial chromatic aberration is also corrected to a modern level.

Field Curvature

The field curvature has a slight bulge in the tangential direction of the intermediate image height. It probably balances the lateral aberration. For details, let's check the balance with MTF.

Distortion

The distortion aberration slightly remains in the direction of the so-called spool-shaped on the plus side. The double Gauss type generally adopted for the standard lens leaves the distortion aberration on the minus side, so it is the opposite direction.

It is less than 1%, so it does not seem to be at the level that I am concerned about in the actual shooting.

Lateral Chromatic Aberration (Magnification Chromatic Aberration)

The lateral chromatic aberrations has been corrected very carefully and there is no need to mention it.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

Let's look at it as lateral aberration.

Considering that it is a small optical system that fits in the GR housing, which has a compact design that becomes flat when the lens is housed, it can be said that the characteristics in the tangential direction (left graph) have already been sufficiently corrected.

The deviation of chromatic aberration in the center of the graph is also small, so the lateral chromatic aberrations will not be noticeable even if it is a small aperture.

The sagittal coma flare, which is an aberration around the image height of 14 mm (top) at the corner of the screen in the sagittal direction (right graph), remains, but it is a story of the corner of the screen, and it is an excellent level.

Spot Diagram

Spot Scale 0.3 (Standard)

This is the result of an optical simulation, but first let's look at the spot diagram.

In the standard scale, it is almost a point characteristic up to the image height of 7 mm, which is the middle area of the screen.

Spot Scale 0.1 (Detail)

Due to the influence of sagittal coma seen in lateral aberration, the image height around 14 mm in the corner of the screen is quite V-shaped.

MTF

Maximum Aperture F2.8

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

After all, the peak of MTF from the open Fno is extremely high, and the position is also perfect.

As expected, with the image height of 14 mm in the corner of the screen, the position of the mountain is shifted, but the height is left, so there is no problem in practical use.

If there is a moderate shift in the + direction, it may be said that the bokeh effect of the background is rather good.

Small Aperture F4.0

If you narrow it down to F4, there will be no deviation even to the image height of 14 mm at the corner of the screen, and you will be able to enjoy high resolution despite the ultra-compact lens.

Conclusion

The GR3x was introduced with a focal length of 40 mm, a "specification of a focal length that is a true standard lens".

It turned out to be a high level of performance befitting a true uncompromising standard.

If you look inside, you will be surprised at the smart and sharp lens composition and performance that inherited the design philosophy of the GR3 optical system.

Moreover, since it is embedded in the same housing size as the wide-angle lens GR3, I am impressed by the enthusiasm of the RICOH development team.

Despite the difficult market conditions for compact cameras, we cannot help but hope that the development of new models of the GR series will continue for a long time.

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.

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