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1978 ISP COMMISSION V INTER-CONGRESS SYMPOSIUM - STOCKHOLM SWEDEN 
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Chosh: meter of the order of 2 micrometers. That is what we used. Later 
on I discovered another nice thing. The diffraction gratings are of known 
dimensions. But the problem is that they give a one-dimensional scale. By 
turning this you can make a grid, and this is two-dimensional. This is 
what we have been using. The original diffraction grating grid would cost 
to the tune of 1500 U.S. dollars, so normally we use a replica grid. These 
replicas are superimposed on plastic material. For limited accuracy, this 
is good enough. This is not for absolute accuracy but once you can cali- 
brate one grid this is fine. The next problem is the determination of the 
third dimension. As one can see from the grating replica we can check X 
and Y, Now what we did was a little twist of the geometry. We put a rep- 
lica grid on the stage plate and give a tilt, center and align properly, 
and then take one picture, then turn the grid through 909 and take the 
other picture, and so on. In this way you get four pictures in which the 
perspective centers are located in four different directions with regard 
to the grid. So you have a multiple photo set-up of the same area. This 
way you can get a control on the third dimension. So here you have got, 
with a diffraction grating, step by step, from one dimension to the second 
dimension, and next the third dimension. That is how we have been cali- 
brating, and tried to face the problem of scale. 
Oshima: Just a short comment on my studies related to microscope photo- 
grammetry and stereomicrography with a scanning electron microscope. 
1) I was involved in studies of microscope photogrammetry ten years ago in 
Japan in co-operation with a doctor in the Tokyo Dental and Medical Univer- 
sity, Prof. Mannen, and the Nikon Co. We have measured the volume and sur- 
face area of neurons stained by Golgi's method, three dimensionally. Now- 
a-days specially designed microscopes for stereophotograms with an annexed 
stereocomparator have been developed by Prof. Mannen with the co-operation 
of the Sokkisha Company. 
2) I have done also stereomicrophotogrammetry with a scanning electron 
microscope. A detailed example was presented in the Journal of the American 
Society for Photogrammetry in August 1970. 
We are also doing fundamental studies using grids which Dr. Ghosh has sent 
to us. When I started this study it was the same time that Dr. Ghosh started 
his work. We are now co-operating. 
Stewart: The radiographic problem is, in fact, as you are probably aware, 
due to the question of the source-object and the object-imaging system dis- 
tance, which, in fact, gives unsharpness in the image due to the radio- 
graphic geometry. We do, in fact, measure from the source position itself 
on the accelerator to the center line of the engine, very accurately. And 
from there we also measure to the imaging plane so that we have immediate 
information on the magnification ratio of every radiograph we take. And we 
also can measure on the radiograph itself, the size of known components, and 
the exact size of the components they were representing, so again we can get 
the magnification ratio that way. 
Doyle: The objects which you are recording are not necessarily in that object 
plane. 
Stewart: Yes, in fact, they are, the way we use this big proton radiography 
system. And then for the image forming plane it is on the vertical center 
line of the engine. It automatically forms that way in the radiographic