[photo-3d] Constant infinity mounting - I

["Dr. George A. Themelis" <drt-3d@xxxxxxx>]

Some of you know that there are two schools of
thought in stereo mounting (this applies mainly for
slide film in 41x101 stereo mounts and 2x2 mounts but
the issue is more general and can be used for any
stereo image - including prints and digital images):  

1. Mount with a constant infinity separation (and let 
   the stereo window fall wherever it may).

2. Mount "to the window" (with the foreground object(s)
   at or close to the stereo window and let infinity fall
   wherever it may.

The first school of thought claims that this is more
natural and comfortable to the eyes.  In real life
when we look at infinity the eyes have always the same
convergence and the same should happen in a stereo
picture, this school claims.

The second school claims that "mounting to the window"
results in pictures which are more pleasing to the eyes.

My opinion on this is that the dilemma is to some degree
artificial and both methods will give similar results
in many photographic situations.  

If a scene photographed contains a healthy depth range
(7ft to infinity in Realist format) then both methods
will produce the same result.  Differences arise when:
a) there is no close foreground
b) there is something closer to 7t 

In (a) mounting to infinity will create a stereo picture
with a large gap between the stereo window and the 
(distant) scene, which some people find annoying and 
might cause ghosting in stereo projection.  People who 
mount to the window tend to reduce this "gap" by 
bringing the film chips closer together, resulting in 
smaller infinity separation and a more pleasing picture.

In (b) those who mount with constant infinity will 
have to accept a stereo window violation.  Those who
mount to the window will never accept this, since for
them the window is a very important compositional element.
They will pull the film chips a bit apart to put the 
foreground at the window. This will result in increased 
infinity separation (assuming that the scene includes
infinity).  In projection this increased infinity 
separation might be hard to fuse but the attention 
should be focused at the window.

Note that situations (a) and (b) are about scenes that
include infinity.  If the scene does not include
infinity (close ups where the distant background is
blocked, macros, etc.) I have no clue how "constant
infinity" is practiced and what is the reasoning
behind it.  In this case I believe most people would
mount to the window, while paying attention not to
exceed the recommended maximum separation.

Personally, I have been mounting to the window but now
I see some advantages of the first method and have 
developed a tool to apply it automatically in RBT
(and RBT-Spicer transfer) mounts.  This will be 
described in the next posting.

George Themelis