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Radiolarians show very impressive skeletons, especially when inspected with the SEM, as shown in the attached photo gallery.
01 - 32: Eozän, Barbados
33 - 74 :Recent, Agulhas Basin, 4732 m
75 - 90 : Recent, Mingulay Reef 186m, Scotland
91 - 92 : Burdigalium, Ortenburg
93 - 112 : Recent, South China Sea, 3465 m
113 - 126 : Recent, west of Virgin Islands, 1815 m
Because of the large depth of field
of a SEM is not difficult to produce stereo image pairs . First you adjust the
image electronically using the feature "scan rotation", so that a
mechanical displacement of the object table from left to right results in a
horizontal displacement on the monitor. The object table must be level. Now
the object is tilted by 5 degrees to the left and the first image is taken (left
stereo image), then the object is tilted to the right by the same degree and
is centered again (right stereo image). The results are amazing!
Click on the images and then print
the enlarged pictures, the stereo image pairs should be 16 cm wide in total
(corresponding with an eye-distance of 8 cm). Look at these images with a stereoscope
(3D-viewer). There is, however, an easier way:
Look at the
stereo pair from a reading distance and then try to look "dreamingly"
through the prints. This way the visual axes of the eyes are parallel and between
the images appears a third image, usually first as a double image. After some
time both these images merge and you will see a three-dimensional structure
popping out of the prints. Experience shows that this approach will first require
some practicing, but if done successfully, the next time it will work much faster.
It is helpful to "try to see" a spatial entity - our brain will do
the rest then. This particular method of image viewing can be done directly
on the monitor (click on the images!)!
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3D-anaglyphs
for red-green glasses, left eye "red"
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First both stereo
images (black-and-white) are processed separately and saved (preferably on
a black background). Then the "right image" is loaded and turned
to "red" using the function <Monochrome>, after that the "left
picture" is superposed and turned to intense green in the same way. After
that <Transparency> is to be set to 50%. Now the red picture can be
seen through the transparent green picture and so it is possible to position
the (upper) green picture in such a way that the middle parts of the images
are at exactly at same level. Now take the anaglyph glasses (left eye "red")
and move the green image horizontally until an optimum stereo effect is achieved.
Finally the images are merged (mode <Normal> ), then contrast is enhanced
and the merged image is saved. Anaglyphs can be used even in large format,
but the picture quality is worse than in stereo images viewed with a 3D-viewer.
In case of colored or very finely structured objects this representation is
not suitable as anaglyph .
It is possible to
stain the second image blue-green (cyan). In this case overlapping parts of
the image appear as white rather than yellow. You should try to find out which
of these methods produces the better result - it depends on the color of the
glasses used.
We add a stereoscopic
pair of images to practise the method explained above (click on the images,
save the enlarged versions, then merge them using PHOTO PAINT or a similar
program). It is noteworthy that the 3D-effect is based merely on the object:
but is independent of the displacement of the images, if the displacement
is limited. When moving the green image further to the left, the shape of
the object does not change, but the object appears more and more in front
of the screen.
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SEM images are very
suitable for stereo photography because of their depth of field, but even
amateurs can produce very nice stereo images by using a stereo microscope
or a common microscope. If a stereo microscope is used you have to work at
low magnification and with a tilting object holder (+ - 5 degrees) you must
make yourself. In case of a common microscope you get stereo pairs by lateral
displacement of the aperture diaphragm. If no corresponding "Abbe illuminating
apparatus" is available, a perforated cardboard strip is used fixed in
an appropriate manner under the condenser. A clean hole can be made with a
core drill.
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