OLYMPUS

Optical Design value Analysis - OLYMPUS Zuiko 90mm F2.0 Macro [no.003]

2022-03-02

This is a performance analysis and review article of the Olympus Zuiko 90 F2.0 Macro.

The design values of the optical system are inferred from patent information and actual shooting examples, and the lens performance is analyzed by simulation.

Professional lens designer Hitoshi 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.

If you are looking for example photos, you can find them at the end of this article.

Overview

One of the Zuiko lens series for the Olympus OM mount, it is a major lens in the mid-telephoto range, split in popularity with the Zuiko 100mm F2.0.

It was usually sold new in stores until around 2000, so it may be a little young to call it an old lens.

Recently, macro lenses are usually 100mm F2.8 and can be used to take an equal-size photo, but until before 1990, there were many 90mm lenses.

The reason for this may be that many manufacturers had 100mm F2.0 and F2.8 lenses in their lineups, so they may have shifted the lens a little and called it a 90mm lens. We do not really know.

Also, we have been under the impression that f/2.8 is the norm for Macro lenses, but to our surprise, this lens is one stop brighter at f/2.0.

The OM series lenses were marketed as having a large number of F2.0 lenses, so I guess they wanted to create a sense of unity with the Macro lenses as well.

However, the shooting magnification is 1/2x (half) and does not go up to equal magnification. 1/2x was the mainstream until the 1980s, but I think all companies moved to 1/1 (equal magnification) with the trend toward AF around the 1990s.

Private Memoirs

At the time when the film OM series was my main equipment, I purchased the Zuiko 100mm F2.0 and passed up on this 90mm.

Naturally, I was torn between the 90mm macro lens and the Zuiko 100mm F2.0, but I thought that a normal lens (100mm) would be better for the infinity side, which is often used for general shooting, and also because I already owned another macro lens.

Owning several macro lenses was an act that was hard for me to comprehend as a young man at the time…

In later years, just before the end of the film OM series (around 2006?) However, it became a mere collector's item and I hardly ever used it. Sad to say.

Document Survey

Now, a search of the patent literature reveals several references to macro lenses from the same period, but since Example 1 of Patent Publication 62-18513 is very similar to the product configuration, we will reproduce it below as a 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

Above is the optical path diagram of the zuiko 90 F2.0.

Nine elements in nine groups, no aspherical surfaces. The structure is a Gaussian type with three lenses on the image side. It is assumed to be a macro lens of the traditional 1-group floating type, in which the front Gaussian portion from the first lens to the sixth lens on the subject side is moved out.

Compared to the Zuiko 100mm F2.0, the number of lenses has increased, and we are wondering which one is better in terms of performance.

Longitudinal Aberration

Graphs of spherical aberration, image surface curvature, and distortion

Spherical Aberration , Axial Chromatic Aberration

Spherical aberration is moderately corrected to a full-correction type, and the g and C lines overlap at the tip of the spherical aberration, which is good because it mitigates the coloration of each other.

Axial chromatic aberration is also corrected to a good degree, with the F and d lines being quite close together. Overall, I have a better impression of this lens than the zuiko 100mm.

Image Surface Curvature

Image curvature is properly corrected, and fluctuations with aperture are consistent with spherical aberration, so there appears to be no problem.

Distortion

Distortion is a bit threadbare because it is in the telephoto range, but it is not a figure of concern in practical use.

Chromatic Aberration

The magnification chromatic aberration seems to be reduced to 2/3 of that of the zuiko 100mm.

Transverse Aberrations

(Left)Tangential direction, (Right)Sagittal direction

It is not particularly comparable to the Zuiko 100mm F2.0 and looks rather good.

The amount of aberration in the sagittal direction depends on the number of lenses, so it is not surprising that this lens, which has more lenses, is better.

Spot Diagram

Spot Scale 0.3 (Standard)

The spot is at a level too small to be seen clearly on the standard scale.

Spot Scale 0.1 (Detail)

Although the F line has a slightly larger spread, the g/C line is well integrated, so there seems to be little color bleeding.

MTF

Maximum Aperture F2.0

It seems to be one step better than the 100mm f/2.0 even at maximum aperture. This may be natural since it is a latecomer and has a large number of lens elements.

Small Aperture F4.0

At f/4, the 100mm is a little better. The 100mm is a high enough performance lens that you won't notice much difference between it and modern lenses.

Conclusion

As a result of the verification while comparing it with the Zuiko 100mm F2.0, it seems that the 90mm Macro has better basic resolution performance.

The 100mm lens is also well put together, but it still has a lot of aberrations compared to modern lenses.

For the purpose of playing with old lenses, the 100mm F2.0 may be more suitable for the purpose. Both lenses had their reasons to be called "famous lenses," but the result gives me mixed feelings.

Ghosting is more noticeable in the 90mm Macro, which has a larger number of elements, but there are no fatalities in either lens, so it does not seem to be a major difference.

I think the biggest gain this time was that I was able to put an end to the zuiko 90mm vs. 100mm issue, which I had been wondering about for a long 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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