P3D Re: active/passive viewers

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Tue, 30 Dec 1997 21:12:25 -0700
>From: fj834@xxxxxxxxxxxxxxxxxxxxx (Dr. George A. Themelis)
>Subject: P3D Re: active/passive viewers

>>>Did you decide on these word choices or is that an industry
>>standard terminology?
>>
>>"The selection technique .. refers to the means for passing the
>>appropriate image to the appropriate eye and blocking the inappropriate
>>image from the inappropriate eye. Two techniques have been developed for
>>doing this: passive means using polarizing glasses, and the active
>>technique in which the viewer wears eyewear incorporating liquid crystal
>>shutters."
>>
>>Lipton, Lenny: "The Crystal Eyes Handbook." (c) StereoGraphics Corp.,
>>1991. p. 43

>Lenny Lipton is a respected name but still don't like the terminology.
>The mechanically passive polarizing glasses are active optically.

No, they're not. A reputable dictionary will inform you that "optically active"
refers to the ability of certain substances to rotate the plane of polarization
of an incident beam of polarized light. For shame, sloppifying the definition
of an existing technical term, in the midst of a lecture on correctness of
terminology! :-)

Polarized glasses are also not active in the engineering sense. Resistors,
capacitors, and inductors can all change an electrical signal, but they are
classed as "passive". Transistors and op-amps are considered active. Polarized
glasses, as unpowered devices, would be passive, while LCS glasses are powered
and active.

I suppose you could call polarized glasses "transducers", but the same claim
could probably be made for lenses and mirrors.

I think you're going to have to try further to define the distinction you
want to make.

John R


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