OLYMPUS

Optical Design value Analysis - OLYMPUS Zuiko 100mm F2.0 [No.002]

2022-03-01

This is a performance analysis and review article of the Olympus Zuiko 100mm F2.

We estimate the design values of the optical system based on patent information and actual photographic examples, and analyze the lens performance through simulation.

Professional lens designer Jin Takayama carefully unravels design information such as optical path diagrams and aberration characteristics, which are rarely seen by the general public, and explains them in depth and gently.

Please enjoy the special information that can only be read on this blog.

Overview

The Zuiko 100 f/2 is a lens that is hailed as a masterpiece of large aperture medium telephoto in the Zuiko lens series for Olympus OM mount.

In terms of focal length, it is probably mainly for portraits, but I like it for snaps as well.

The 100mm focal length is a specification that evokes a sense of nostalgia. This may be because we haven't seen many single focal length 100mm large aperture products in recent years.

Since the standard macro lens is the 100mm f/2.8, the number of 100mm single focal length lenses has been decreasing, probably due to the fact that many companies have taken into consideration the overlapping specifications.

The Zuiko 100 F2 has a hefty weight in your hand, but compared to modern lenses equipped with AF and image stabilization mechanisms, it is a cute size.

However, it has a wonderful sense of mass and density in the glass and metal that is typical of old lenses, and it is a texture that I would love to collect.

Zuiko lenses with small apertures are often listed as masterpieces, but in the mid-telephoto focal length range, the Zuiko 100mm f/2.0 and the Zuiko 90mm f/2.0 are both listed as masterpieces.

Private Memoirs

I bought this lens around 2000, and I remember that I had a hard time deciding between it and the Zuiko 90mm f/2.0 macro lens, which was also a famous lens.

Since I had other lenses in other mounts for macro, I ended up buying the Zuiko 100mm f/2.0.

I vaguely remember the day I used this lens for the first time. The image I saw through the viewfinder was already beautiful, and I intuitively knew that I would be able to take good pictures with it.

At that time, film was still in its prime and lenses with good performance were limited, so I was very impressed.

In the end, I bought the 90mm lens later in the year, so I would like to analyze and compare the 90mm macro lens at a later date.

How many women I photographed with this lens is information I will take with me to my grave.

Document Survey

In a comprehensive search of patent documents from the late 1970s, we found two cases with similar cross-sectional views of the product, both of which were granted for the feature of improved performance at short distances.

The specific improvement seems to be the introduction of floating focus, in which the two lens groups are moved separately at the same time during focusing, to achieve uniformly high performance from infinity to short distances.

Without disassembling the lens, it is impossible to determine if it has floating focus, but let's assume that it does. I'd be happy if it was…

The shape of the cross-sectional view is similar to that of the patent document, and based on the publication date and the performance of the product, I expect that Example 1 of JP57-111506 is similar to the product configuration, and try to reproduce it as the design value.

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 zuiko 100 f/2.0.

It is a typical Gaussian medium telephoto type lens with 7 elements in 6 groups and a convex element added to the front side of the double Gaussian type.

The original Gaussian type lens is suitable for a focal length of about 50mm, but this lens has been extended to a longer focal length of 100mm, so the Gaussian-like symmetrical structure is slightly lost.

Nevertheless, it is possible to secure performance up to 100mm.

Looking at the lens materials, a special low-dispersion material is used for the second lens. Nikon calls it ED glass.

When a special material is used, it is likely that a special name will be added to the product name, but I think Olympus is being modest in not including it.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

Spherical aberration is sufficiently corrected.

The key point is to keep the correction at a slightly full level, because if you correct more than this for this number of lenses, you will lose the balance with the image surface curvature when you stop down the aperture.

As for the axial chromatic aberration, I was tempted to set the g-line a little more to the positive side, but I guess this was done in consideration of the balance with the magnification chromatic aberration.

Image Surface Curvature

The image surface curvature is in the large aperture category, but it is properly corrected.

Distortion

Distortion occurs on the string side as the focal length gets longer, but at 100mm it is corrected to almost zero since it is not that long a focal length.

Chromatic Aberration

However, since magnification chromatic aberration is often not noticeable at wide apertures, I don't think it will be an issue in practical use.

However, since magnification color is often not noticeable at maximum aperture, I don't think it will be a problem in practical use.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

The Fno value is well compensated without any peculiarities. This is the reason why it is called the best lens.

Spot Diagram

Spot Scale 0.3 (Standard)

I expected red aberration to be noticeable based on the axial chromatic aberration, but when I looked at the spot, the balance seemed good.

Spot Scale 0.1 (Detail)

MTF

Maximum Aperture F2.0

The MTF is already high from the aperture, and the peripheral focus is consistent. It certainly has the performance of a certified masterpiece. It may not be as interesting as an old lens, but…

What is a little interesting is that the performance in the center and the periphery are quite homogeneous and consistent.

Normally, only the center of the image is enhanced, but this lens is homogeneous and high performance throughout the entire image area, which I think leads to a particularly wonderful image.

Small Aperture F4.0

Since the lens is already fully configured at maximum aperture, stopping it down does not make a significant difference, but it does reduce image curvature. This is a performance that would not be out of place today.

Conclusion

The performance of this lens is so impressive that I was surprised to see how much performance can be achieved with such a small number of lenses.

In actual photography, the performance is flawless, but compared to the ultra-high performance lenses of recent years, there is a slight increase in axial chromatic aberration, so you can enjoy a slightly rounded, gentle rendering.

The performance of this lens was such that it was recognized in many places as one of the best lenses of its time.

Sample Picture

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

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