Free Viewing Stereo Cards

[P3D Jim Roberts <xjim@xxxxxxxxxxxxxxxx>]

I sent this to Hugues, but then thought it might be of more general interest, 
as I think I have seen several people complaining about not being able to
free view stereo cards and other images requiring a large amount of divergence.

For me, free viewing stereo cards was a skill that had to be learned. It was
not hard for me to view smaller images (such as the images in Waldsmith's
book), because of the smaller divergence, but I had to train the muscles in
my eyes to be able to handle the larger divergence.  

What worked for me was to mount a stereo card on the wall and then step back
until I could free view it (maybe 5 feet or so) and then to _slowly_
approach it, while keeping the images merged and in focus.  You can feel the
strain as you get closer because the eyes are not used to being diverged and
yet focused on a close object.

With practice, the eyes' ability to handle the divergence got better and
better, and after a few weeks, I could just pick up a stack of cards and
start viewing them quite comfortably.  As in any muscular exercise, this
should be done in stages so as to avoid causing any strain or damage.
Beyond the simple toning of the muscles, there is a skill involved which
needs to be trained as well - the skill to decouple focusing and vergence.  

If you happen to have narrowly set eyes, no amount of practice may help, because
normal eyes have a very small physical capability to diverge wider than
parallel lines of sight.  I've heard numbers in the range of a couple of
degrees, though
I think mine can handle more.

Hope this helps.

Jim


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