Re: Ortho Seat

[P3D Bill Davis <bd3d@xxxxxxxxxxxxx>]

In Digest 2368,  P3D Bob Aldridge <bob.aldridge@xxxxxx> wrote:

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


This would seem the proper method for those images where the scene extends
to infinity.  Infinity would then appear to be at infinity. This even makes
sense to my feeble mind.  :--) 

A bit of a problem I have understanding this deals with close-up or medium
images where the whole scene is limited to a few feet or yards or less in
depth (Aunt Mildred in her rose garden with the outside wall of the house
behind her, for instance).  

There being no true "infinity" in the scene, would you still place the far
points of the image 65mm apart, regardless of their distance from the
photographer?  In this case, the house would appear to be at infinity;
wouldn't even the near points appear far behind the window? 

How does one project macros?  Put the near point at the screen or the far
point at infinity?  It would seem that the projectionist would be at odds
with the photographer/mounter in some instances.

Wouldn't it be better to put the near points or the window at the screen,
and let the far points take whatever position they will?  After all, all
images have near points whether or not they show anything near to infinity.

Or am I just confused?

>
>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)

So really, to save oneself from a lot of trouble when entering the stereo
theater (or stereo theatre, depending on the address) one should just look
for the person wandering around with measuring tape, slide rule or
calculator, pulling their hair out and muttering.  Wait till they finally
choose a spot to sit down, then sit in the next chair over.  :--)

>
>See Ferwerda for the ratios...

I hardly ever see him.  I've got his book, though.  I'll check that.


>
>Bob Aldridge
>---
>
Thanks, Bob.

Best regards,

Bill Davis
mailto:bd3d@xxxxxxxxxxxxx



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