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 America. In this case left and right images are reversed, so you have to cross your eyes to see them in stereo. This can give strain on the eyes, and will be even unhealthy in the long run. The advantage is that images can be bigger, depending on how far you can cross your eyes.

 

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.         

 

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