Ortho Seat

[P3D Bob Aldridge <bob.aldridge@xxxxxx>]

Richard M. Koolish posted:

->Michael Kersenbrock writes:
-> 
->> Are you sure he was close to the "ortho seat"?  Whenever I've done
->> the calculation for my 5" lens'd setup one almost has one's nose
->> to the screen to be ortho.  Well, not quite, but close.  A few rows
->> in front of the projector sounds like a stretched spot.
-> 
-> 
->    Here's my question:
-> 
->        Lets say you had two projectors, one with 5" lenses and
->    one with 4" lenses.  If you set up both projectors so the
->    on screen images are exactly the same size and in the same
->    position, would the ortho seat be different for each projector?
->    If not, then the ortho seat must depend only on image size, and
->    not projector distance.
-> 

I think you've hit the nail on the head, here!

It has become traditional to just match the left and right frames on the
screen in projection with no regard to image size. This is incorrect,
and leads to excessive infinity separation with projected images over
about 4 feet wide. 

In practice, the infinity points should be set about 65mm apart so that
the audience view them with parallel lines of sight. 

What this does is to move the window forward of the screen.

In any event, the ortho seat is placed at a distance from the _window_
that depends on the ratio of the camera film aperture to the _camera_
lens focal length. The projection equipment has no part in determining
the positioning of the ortho seat - it's all in the taking (and masking,
if this is not done in the camera)

See Ferwerda for the ratios...

Bob Aldridge
---
 * POW 2.0  0007 * PUBLIC SPEAKERS do it orally


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