THE FREEVIEWER'S ASSISTANT - Part II

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

THE FREEVIEWER'S ASSISTANT - Part II

What does this thing do?  How does it work?  Simply stated, it shifts 
the view (changes convergence) of one eye.  You place it in front of 
your right eye.  The left eye looks directly in the left image.  The 
sight of the right eye, through a set of two mirrors, is directed to 
the right image.  The two images overlap... 3D!!!

To understand how it helps, one should first realize what the problem 
in freeviewing is.  In both parallel or cross viewing, the eyes focus 
(accommodate) at the stereo image plane, while they converge past this 
place (in the case of parallel-viewing, all the way to infinity or 
beyond in some cases) or before this plane (in the case of cross- 
viewing, somewhere between the eyes and image plane).  In real life 
convergence and accommodation go hand by hand, i.e. we focus where the 
eyes converge.  The difficulty in freeviewing is to break the link 
between accommodation and convergence.  This can be done, but it 
requires practice and for many people it is tiresome or cannot even 
be achieved.

The "Freeviewer's Assistant" makes "Freeviewing" a breeze because it 
restores the link between accommodation and convergence.  By shifting 
the convergence of the right eye it allows the eyes to converge and 
focus at the plane of the stereo image.  Hence, it makes "Freeviewing" 
effortless.

Here is what Alan writes about it:

"Why does it work?  It is doing what any beamsplitter does except that 
it only moves one of my eyes out (rather than both).  My left eye 
looks normally at the viewcard while the stereoscope moves my right 
eye further out.  So I am looking at the viewcard with my eyes spaced 
the same distance apart as the photos on the viewcard.  I have seen 
other dual beamsplitters do the same thing, but never a single one 
over one eye... The final 3-D image is identical to a freeviewing 
image.  You see three images, the one in the middle is the 3-D image. 
I have designed a mask that eliminates the two adjacent images, so 
you see only the one 3-D image."

A problem of terminology arises here... A device is used to redirect 
the sight of one eye.  Is that "freeviewing"?  Technically, no.  
Considering however that one eye is really freeviewing, while the 
other is only assisted by mirrors (not lenses) this device is as 
close to freeviewing as possible.  If one insists to call it a 
stereoscope, perhaps the term one-half stereoscope is more appropriate.

While T. Brown used two fixed mirrors in his stereoscope, Alan chose 
to make it more flexible by making one mirror pivoting, instead of 
fixed.  This allows you to freeview a wide range of images, from 
Realist 35 mm chips up to projected size. 

As Alan pointed out in a recent posting, the FREEviewer's Assistant 
is not FREE!  Some people would say that it is rather expensive 
(considering its size)  since for the same price one could buy a 
full-sized Holmes stereoscope.  For me, the price is justified just 
because it uses high quality first surface mirrors, and is hand-made 
from mahogany and brass (it also includes a storage box and 
instructions).

>From a practical point of view, considering what this ingenious little 
device allows you do things that you cannot even magine with a Holmes 
or other stereoscopes, the "Assistant" is worth every penny, for me!

If your are still following this thread, please proceed to the next 
installment explaining all the wonderful things you can do with it...
and how it is changing my computer 3d views :)...........

-- George Themelis


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