Making
stereopairs and anaglyph loop-animations
with
Computer Aided Design
General
Stereo images with CAD are sometimes usefull and always fun.
Here a brief summary of some
general stereo matters.
1.
History
Stereophotography is as old as photography
itself and always has existed as a ‘para-photographic’ activity with up and
downs in popularity throughout the 19th an 20th century.
There was a revival in the 1950’s when
a.o. View Master and Realist came on the market with smallfilm diapositive
systems. Famous stereo-propagandist in that period was Dwight D.Eisenhower who
always carried his Realist camera with him.
2.
Slide projection and divergence
Projecting slides has always been
the favorite way of looking at stereo’s for the serious amateur and pro’s. It
works with polaroid filters before the lenses of the projector and you look at
them with polaroid glasses. As with
anaglyphs, the foreground (or objects in the foreground) of the left and
right image should coincide on the projection screen, resulting in a diverging
distance separation of the two images towards the infinity point. This
divergence may seem strange in a converging perspective-world but it is
the logical consequence of the stereo-parallax.
3. Digital
photography and beamer projection.
A new and very promising
development is the projection of digital stereophoto’s with two synchronized
‘beamers’ (beamer= projector of computer images). Given the enormous growth in
popularity and quality of digital photography one might wonder how long the
usual slide projection will survive in the future. Two small digital camera’s
can easily be combined into a handy stereo device.
4.
Shutter glasses
Using special hardware, the left
and right images appear rapidly alternating on your computers/tv -screen and
you look at it with a special pair of glasses with synchronized alternating
translucency of left and right. The
system is not a big succes so far although second hand gear is now available
and very affordable. The system can be a good alternative to dia projection on
a small scale.
5.
The Stereo Window
Close your left eye and look with
your right eye out of your office window along the left edge. Now close your
right eye and look along that edge with your left eye. Ýou will note the
difference: you see more with your right eye. The other way around of course
for the right edge of your office window. This is the stereo -window effect.
Stereo slides have to be mounted precisely to
imitate this effect. Fortunately with CAD this happens automatically,
but only if you apply correct stereo rotation for the second image. See also protrusion
later on.
6.
Hyperstereo (lilliputism) and Macrostereo (giantism)
Hyperstereo is
the effect you get when the distance between the two lenses of a stereo camera
is wider than the eye width . With normal eye width (6.5cm) the stereo effect
is limited to about 65 meter. With a lense-base of 1 meter the stereo effect
already stretches out to 1 km. This will give stereo’s with a maquette-effect
and people looking like tin soldiers.
Macrostereo is the opposite of
lilliputism: the 2 lenses are now very close. Photographing insects for
instance with lenses at 1.5 cm makes
them look like giant stereo-monsters.
7.
The 1-in-30 rule
This rule of thumb says that the
nearest object(s) in a scene should never be closer to the camera than 30 x
lense-base. So for a standard stereocamera with 6.5 cm lense distance this
means 30 x 6.5=195cm (about 2 mtr). Everything closer than 2 mtr will not be in
stereo and will cause conflict with the stereoscene.
8.
Parallel focus viewing
Staring at a stereo pair and focussing at the same time gives you a
perfect stereo without glasses. This
seems to be the favourite method amongst European stereoscopists, but it
demands some practice. Disadvantage: images never can’t be larger than about
7cm (eyewidth).
9.
Cross eyed viewing
This method is by far favorite in
10.
Anaglyphs
Left and right are blended into one image in red and cyan.
Look at it with red (left) an cyan (right) glasses, and you get a perfect
stereo . The cyan glass eliminates the red while the red glass eliminates the
cyan .
Working with
CAD
The subject is too extensive to discuss
here in detail. Some prior knowledge of CAD may be advisable but is by no means
absolutely necessary. With a good 3D-program it won’t take long before you can
make your first stereopair. My favourite programs are Rhino3D, TurboCAD, 3DMax
and Bryce, but there are many more. Some free CAD programs can be found here. Don’t forget to pay a visit to the 3D-Cafe.