Ortho or not ortho?

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

Something else, regarding Tim Maffia's viewer question... 

Ortho is defined as the situation where the FL of the viewer matches the FL
of the camera.  Here are some common FL of 35 mm image lenses:

FL (mm)    Camera/Viewer/Projector
-------  --------------------------------------------------------------
35          Realist and most stereo cameras (RBT S1 too)
45-55       Common FL for 35 mm normal lenses
44-47       Good viewers (Realist, Revere, Kodaslide etc.)
50-55       Star D, $3 plastic, most viewers with plastic lenses
35          Realist gold button
100         4" lenses in TDC projector
125         5" lenses in TDC projector
250          Common freeviewing distance (10 inch)

Notes:  

1. Most viewers have longer FL lenses that the common 35 mm lenses in most
stereo cameras.  It is not easy to make a good viewing lens with very short
FL and, if you do make one, it is not fun using it! (see Gold button)  

2. The better viewers from the 50s have shorter FL lenses thus getting
closer to ortho.  

3. In projection with a TDC the projectionist cannot see an "ortho" image
from the projector level but the audience can do it if they sit
sufficiently close to the screen.  

4. Freeviewing is anti-ortho!!!

Whether you like ortho it is up to you... Most people find longer FL
viewing more comfortable and Tim is a good example!  I plan to construct a
viewer with 100 mm lenses to see if it simulates typical projection viewing
conditions better...

George Themelis


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