P3D Re: Transposed and Pseudo

[jacob@xxxxxxxxxxxxxx (Gabriel Jacob)]

Mark writes:
>If anybody would like to offer a concise explanation of why Nimslo
>and beamsplitter shots are different in this way, I would like to
>hear it.

Okay, I'll try to explain this, hopefully someone else can explain
it much more simply. Basically the key to understanding this is that
the image on the film is upside down. Of course this is easy to see
by projecting an image with a magnifying glass on to a piece of paper
or by keeping the camera shutter open and looking at some some
translucent material placed where the film normally goes.


With two lenses the images are upside down in their corresponding
frames. Turning them right side up results in the left frame now
being in the right side and the left frame being on the right side.
The film is now cut and transposed back to their correct positions.
See example below.

Example 1 with a Nimslo (two lenses and two individual frames)
                 
  [ ][ ]        -two individual frames on a roll of film                
                        
  [q][p]        -q is on left side (left lens) of film as seen from
                 back of camera, image is upside down
                -p is on right side (right lens) of film as seen from
                 back of camera, image is upside down        
                
  [d][b]        -turning [p][q] 180 degrees clockwise results in the
                 images being right side up
                -this results in [d], originally on right, now on left
                 and [b], originally on left, now on right
              
  [b][d]        -cutting [d][b] and transposing them so they are
                 in their original left-right orientation and right
                 side up, image is now in correct orientation

                
A beamsplitter turns upside down both images as one (since it uses one
lens to record two images on one frame). This results in the left side
of the beamsplitter being on the right side of the film frame and
the vice-versa. See example below.
               
Example 2 with a Beamsplitter (one lens and one frame)
          (not applicable to Loreo or Argus cameras)

  [  ]           -one individual frame with two images
               
  [pq]           -q is on right side (left side of beamsplitter) of film
                  as seen from back of camera, image is upside down 
                 -p is on left side (right side of beamsplitter) of film
                  as seen from back of camera, image is upside down
                                 
  [bd]           -turning [pq] 180 degrees clockwise results in images
                  being right side up, image is now in correct orientation

Now if any of this made sense, you can be a Rubik's Cube expert! ;-)
                 
Gabriel


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