Re: Mounting discussion

[bercov@xxxxxxxxxxx (John Bercovitz)]

Tim Smith writes:

>> Could we have a discussion comparing mounting to the window versus
>> mounting to infinity?  

> As a newcomer I'm a little puzzled by the discussion and would like to 
> learn more.  

Great!

> Is this "window" referred to as the stereo window, mask window or 
> holding the camera out the window :-).   

This is the stereo window, not the apertures in the stereo mount or the
film gates in the camera.  You can think of the apertures in the stereo 
mount as forming just another object in the view (a window frame if you 
will), located at a relative distance in the view just as is any other 
object.  Its relative position in depth is determined by its separation 
just like any other object.  If infinity is at 63.5 mm separation and 
the apertures are at 62 mm separation, for instance, you can lay out the 
geometry and find that the window thus formed is at 1.6 meters for 38 mm 
lenses.  Nominally the window is at 2 meters or 7'.

> Does mounting to infinity mean that you align two distant points as 
> opposed to two objects in the foreground?

> After reading the mounting instructions from Reel-3D I though it was
> as simple as centering up the left chip and aligning the right chip 
> with the closest object according to the gauge.  

It can be that simple.  The Reel 3D gauge has two lines for the right 
chip.  One is the infinity line, which you should use if you can, and 
the other is the nominal 2 meter or 7' line, to the left of which should 
lie no right-chip object under peril of having said object lie closer 
than the window (pop out of the window).  If the closest object in 
reality _does_ lie closer than 7', and you have no distant objects, 
then you can align the closest object to the 7' line.  Then you take 
the opposite tack and say no object should lie to the right of the 
infinity line.  This type of alignment (7' alignment) would make your 
eyes diverge in the classic setup if you had objects in the distance, 
but we are only allowed to use this type of alignment if there are no 
objects in the distance.

If you have objects at infinity and also have objects closer than 7', 
you have a choice.  You can either align the closest object to the 7' 
line and diverge to infinity (no big deal if it's not too much) or you 
can use a close-up mask.  I'm not a real big fan of Realist-type close-up 
masks so I'll let a projection-oriented stereoscopist explain why they're 
made that way.

John B


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