From: jonas@world.std.com (Jonas R Klein)
Subject: TECH: Parallax question about a quickie HMD hack
Date: Mon, 10 May 1993 08:11:39 GMT
Organization: The World Public Access UNIX, Brookline, MA



This doesn't seem to be quite the right newsgroup... Can someone point
me to something better?

I just duct-taped a Sony Watchman to a byclyle helmet along with a
mirror and a lens to focus the virtual image at about 10 feet or so.
The mirror sits in front of one eye, and the other eye is free to see
the real world.  This should produce the illusion of the tv image
projected onto the wall or whatever I'm looking at.  When I try to
focus on the tv screen, though, my other eye moves inward, as if the
image of the tv was only a few inches away.

Why does this happen when when the only distance information present
(the image focus) locates the image at least 10 feet away?  Does the
image existing only in my right eye draw my left eye to the right
toward it?  i.e., does my brain think the image is in such a position
that it is centered in my right eye, but just out of view of my left,
and therefore very close?

And on a related note: what kind of optics are used in current HMDs?
I assume LCD's are the most common display; will a simple positive lens
in a focal length away from the lcd suffice? (I had little luck when i
tried this a few years back with an lcd, but it works marginally with
a CRT Watchman.)

Thanks,
+Jonas Klein