Re: Electron Microscopes

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

>>I don't think that you can make stereo with a transmission electron
>>microscope.  What you need is a scanning electron microscope (SEM).
>
>Could you elaborate on this (the difference between transmission & scanning
>microscopes, I mean).

With a Ph.D. in Materials Science (in case you wondered!) I have used both
but have only taken (and still taking) stereo pairs with the SEM (scanning
EM).  It's not true that you cannot take stereo pairs with the TEM!  You
can!  But you are looking at an image formed with the beam going through an
electron-transparent sample.  Unlike the TEM that forms an instantenous
image from a beam going through the sample, the SEM "slowly" builds up in
image by scanning the surface of the sample.

The fascinating pictures of bugs that you've seen are taken with the SEM. 
This is an amazing instrument that allows you to see and photograph most
objects from 15x to 100,000x with an incredible depth of field.  Using the
SEM for 3D is what started my interest in stereo photography.  My Ph.D.
thesis is loaded with SEM stereo pairs (of fractured metal surfaces) but my
thesis advisor was stereo blind and could not properly appreciate the 3d
aspect of my work!

I have written an unpublished report with Instructions for Recording,
Viewing and Analysing SEM Stereopairs but there is no sense is giving more
details here... other than say that the basic principle is to tilt the
sample by 5 to 10 degrees between the two (R & L) exposures.  

(What? Tilt?  After I said that you should not tilt the camera?  Well, yes,
under higher mags you are working with essentially parallel projection 
conditions and there is no keystoning...)

George, happy that he finally posted something work-related!!!


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