Re: Cardboard cutouts and backdrops...

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Tue, 2 Sep 1997
>From: P3D Gregory J. Wageman writes:
>
>
>I wrote, regarding the decoupling of vergence and accomodation:
>
>>>Is this really a cue that one must "learn to decouple"?  The fact that
>>>a stereo slide is planar while disparity is preserved produces the effect,
>>>but the implication of "learning to decouple" these is that one couldn't
>>>succesfully view a stereo slide in a viewer until then.
>
>Larry Berlin replied:
>
>>*****  I think you missed the point................
>
>No, Larry, I think *you* missed the point.  John used the phrase "must
>learn to decouple".  

******  At this point I've lost memory of the specific thread that preceeded
your comment. It was my impression however that John was talking about
(among other things) some of the pleasures associated with stereo viewing
and learning to decouple various aspects was a part of that pleasure. If
that wasn't in his specific previous statements, then I was extending what
he said unintentionally.


>............ if this didn't happen automatically, then one's initial attempts
>to view a stereo slide in a viewer would not be entirely successful (since
>focus would presumably change with vergence, the slide would go in and
>out of focus as vergence changed).  This is however not the case.

******  Yes fortunately!

>...............
>>Viewing a stereo slide in a viewer requires relatively little decoupling of
>>convergence and accomodation. Freeviewing the same slide set would require
>>decoupling vergence with accommodation to a much more significant degree. 
>
>I disagree.  Viewing a slide in a viewer requires the same type of
>decoupling of vergence and accomodation as freeviewing.  In both cases,
>the eyes are focused on a fixed plane, while vergence changes depending
>upon the depth of the object of interest in the scene.  What is different,
>however, is the plane of focus, being at "infinity" for a slide in a
>viewer, while at the real distance when freeviewing.

*****  I guess my point was more to the fact that freeviewing is a
significantly different vergence. Using a stereo viewer places both images
into essentially the same place (infinity) allowing relative vergence to be
easy and almost natural. Freeviewing however creates it's own plane of
vergence much different than where the image itself is positioned. This is a
considerably different circumstance with a much greater decoupling. Crossed
viewing for example places the vergence about a foot or two in front of the
face while the accomodation has to allow for the actual image which is at
least twice as far away. 

The naturalness of using a viewer is occasioned by it's optics, etc,
allowing very little decoupling to be required. Accommodation is the same
relative to the entire image which optics places at the apparent center of
vergence. Vergence can be specific to any part of the image without changing
accomodation, which is your point. In freeviewing it has to change
drastically in order to get started.

>............
>The only thing one "learns" in using a viewer is to get used to the
>somewhat unnatural feeling of doing so.  Freeviewing, on the other
>hand, is entirely a "learned" process because of the complete lack
>of optical assistance in the requisite decoupling.
>

I agree with you but still think the decoupling is much greater in
freeviewing. That's more than a lack of optics which creates an infinity
circumstance. A slide viewer uses the idea of infinity focus because in
normal circumstances we scan around a distant scene easily without changing
accommodation. We already know that skill. That makes it easy.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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