of replicas, since the original surfaces cannot be 
examined directly.  Evaporated silicon monoxide was 
found to be capable of forming good replicas. The 
surface of the replica was identified and located 
by the deposition of & "decoration" of condensed 
heavy metal particles formed by evaporation of a 
small quantity of suitable metal in vacuum. Gold/ 
palladium wire wrapped round the tungsten filament 
produced & suitable deposit of about 1 nm average 
thickness, but with an open reticulated appearance 
of à spacing around 15 nm. 
The AEI EMÓG transmission electron microscope used 
to produce the stereo pair micrographs was equipped 
with a high tilt cartridge to maximize the stereo 
effect. The exposures on glass plates were printed 
on glass plates or high stability film and measured in 
a simple folding mirror stereoscope (Hilger and Watts 
SB180). Corrections were applied for the apparent 
tilt caused by variation of magnification. 
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Figure 25 Surface topography of three gold films by 
stereo electron microscopy, (a) 40 nm, 
(b) 29 nm, (c) 16 nm mean thickness. 
Vertical scale expanded to emphasise the 
relief. 
Figure 25 shows the results of measurements on gold 
films of three thicknesses and indicates that greater 
surface undulation occurs with increased thicknesse 
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Figure 26 Groove shape of X-ray diffraction grating. 
(a) Stereo electron microscopy 
(b) "Talystep' 
96 
A typical groove profile is shown in Figure 26, 
comparing the measurements made by the stereoscopic 
technique with the profile indicated by the "Talystep" 
profile measuring instrument. There is agreement in 
the results, but it should be remembered that the 
dimensions of the Talystep stylus limits the 
resolution of detail at this scale. 
Reference 
15 Butler D W, "A stereo electron microscope 
technique for microtopographic measurements", 
Micron, 1973, 4, pp 410-424. 
Conclusion 
In this paper, ten examples of unconventional imaging 
techniques used for measurement purposes have been 
briefly described. They serve to show possible ways 
in which photogrammetry has been extended, or ways of 
making use of the existing techniques of 
photogrammetry in these fields.