P3D VM Interocular or what a fraction of a mm means

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

Steve Berezin <sbere@xxxxxxxxxxxxx> wrote:

>I measured both the Viewmaster Model L which most people can fuse and
>the ViewMaster Virtual Viewer which many people cannot and found their
>interocular was Virtually ;-) identical. I did find the infinity
>separation of the images was a tad greater than the interocular in both
>the viewers.  That is why I assume focal length plays a roll in this.

Yes, of course.  As Abram likes to say, it is a matter of
angles.  The shorter the FL, the larger the angular deviation.
That's why I am convinced that a high magnification (low FL)
VM viewer (like the Dukes viewer) must have an interocular
adjustment to adjust for variations in infinity separation
between different images.

But your statement that you found the interocular virtually 
identical, motivated me to pull out a few VM viewers and make
my own measurements.  Here is what I found:

- Window separation of VM reels: 65mm.  This is the separation of
  the openings in the reel.  The infinity separation is wider
  than that.  I don't know of any standard.  My guess is 1mm wider, 
  but some of the very "depthy" VM images certainly have more.

- Interocular of Virtual: 64.8mm
- Interocular of other cheap current VM viewers: 65.0mm
- Interocular of model F: 65.0mm
- Interocular of VM Model D: 66.0mm
- Interocular of deWijs as I have adjusted it for my most
  comfortable viewing: 67.0mm

So, the Virtual viewer has the shortest IO of all measured VM
viewers, shorter than the window separation of the images.

HOW DOES ANYONE EXPECT A HUMAN BEING TO BE ABLE TO FUSE THE
STEREO IMAGES WITH THIS VIEWER???

Actually, I am surprised I can even fuse the foreground points,
given that my eyes are called to diverge even for these!!!

The model D is much better at 66mm.  The 67mm that I have set
my deWijs viewer allows me to view all the images of the demo
Reel that came with the Virtual.

I think someone should ask VM to reconsider their design of
the VM viewers!  (It is too late to redesign the standard VM 
reel, but not too late to redesign the viewers)

George Themelis