Thanks, Richard for this interesting link !
Tale #25 alludes to the request by professor Koana mentioned in the opening of the linked tale #85:
The Kanji characters used in those days had a larger number of strokes and required a resolving power several times higher than that needed for the letters of the alphabet for accurate identification.
Interestingly tale #85 mentions modulation transfer functions "MTF" in some detail:
" Now we'll take a quick look at MTF characteristics. I'll cover the results seen at 30 lines/mm. First, reaching 87%, MTF value is very high at the center of the frame at a distance of infinity, but gradually drops toward the edges. Contrast still measures approximately 55% at a height of 50% the total image height, and remains approximately 33% at the extreme edges. On the MTF chart, the image-plane average value is highest at a magnification of -1/30× suited for shooting portraits. However, the variation from those at infinity is very small. There is no deterioration in MTF characteristics from near infinity to a magnification of around -1/10×, which makes the Micro-Nikkor Auto 55mm f/3.5 an excellent all-purpose lens for standard focal lengths. The peripheral MTF peak begins to move in the negative direction in accordance with changes in the curvature of field as we move closer to achieve a magnification of -1/10× or greater. As a result, MTF characteristics of the same plane appear to deteriorate. However, as I mentioned earlier, depth of field is extremely shallow with close-up photography. As such, the only flat subject that would lie on the same plane is a newspaper. When photographing a three-dimensional object, the MTF value for the focus position at each image height is what's important. Therefore, a perfectly flat image plane is not really necessary. I found Wakimoto's design to be outstanding in that respect as well. "
The statement " a perfectly flat image plane is not really necessary " towards the end is a bit surprising in view of making micro fiche copies of Kanji text.
In march 2020 I made MTF measurements for my 55mm f/3.5 micro Nikkor. As usual in Bayer green spectrum at imaging ratio 1:33 for 10, 20, 30,40 and 50 cycles/mm. fullt race is meridional direction and dashed sagittal. Its through focus from front focus 64mm left to back focus 64mm to the right, and also stopped down at f/5.6 and f/8 in addition. I would say that stopped down to f8 there is not much left to be wished by the standards of today.
If you consider this lens to reproduce old 35mm slides, imaging ratio 1:1, then there is a practical advantage to modern micro Nikkors with internal focus.
For this old lens, with the internally fixed lens group to be extended for focus, a special case arises at imaging ratio 1:1. The object sensor distance is at the minimum (~ 4f ). Precise focus can be obtained by either moving the object or the camera, but not with the focus ring ! The focus ring adjusts the precise imaging ratio in this special case.
A modern lens with internal focus (changing focal length) behaves differently. You can auto-focus for conveniently get focus accurate enough. And the object sensor distance acts primarily on the imaging ratio as usual.
