Summary: How to explain phase determinaton and Fourier

Nobuhisa Watanabe nobuhisa at
Sat Sep 17 23:31:22 EST 1994

I have received ten responses by e-mail for my post. And the half of them 
are asking to post the summaries here. 

The answer for the question: "How can you get an electron density maps 
from the diffraction spots?" is,

1) Diffraction.
Almost all wrote the only one way to explain the diffraction is using He-Ne

laser with some meshes, slits, or photo reduced two dimensional patterns.

2) Phasing.
I think there is no good idea to explain phasing to the "public".
"Using some tricks" is enough?

3) Fourier transform.
Using Prof. Henk Schenk's overhead projector method might be most

>he had some sheets for the overhead projector with some parallel lines, 
>representing the waves.
>He put them ('quite randomly') on top of each other and the result was a
>rather featureless, blurred picture. Then he started to explain about 
>direct methods etc. and after that he put the sheets on top of each other 
>again (but this time properly aligned i.e. all corners on top of each other)
>and the electron density map of a benzene ring emerged ...

I know what it is. But I do not know there are any references. Please post 
here if someone knows any references. And I wonder if someone copy this to 
a nice software using graphics? 

#I found I made a mistake when I post the previous question. 
#I am very sorry for inconvenience.
Photon Factory, Natinal Laboratory for High Energy Physics
e-mail: nobuhisa at

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