99 6
. Fig. 6.7 a Schematic illustra-
tion of projection distortion of
tilted surfaces. b Illustration of
foreshortening of familiar objects,
paper clips (upper) Large area
image at 0 tilt; (lower) large area
image at 70° tilt around a horizon-
tal tilt axis. Note that parallel to
the tilt axis, the paper clips have
the same size, but perpendicular
to the tilt axis severe foreshorten-
ing has occurred. The magnifica-
tion also decreases significantly
down the tilted surface, so the
third paper clip appears smaller
than the first (Images courtesy
J. Mershon, TESCAN)
A
B
C
D
A* B* C* D*
In the SEM image, arrows spanning
A, B, C, D appear to be same length!
Projection
Distortion:
Foreshortening
Scan Rays
S*
Cross-section
through rough
specimen
a
Strue =
b
tilt
Tilt Axis
0
70 ºtilt
6.4 · Image Defects