[photo-3d] Re: Pulfrich-Info

[Abram Klooswyk <abram.klooswyk@xxxxxx>]

>I would like to know if the Pulfrich system has actually any patent. 
>I understand that this old phisical propertie is public domain. 
>Am I wright?

>>May be, some glasses, are patented. (...)

The Pulfrich effect was published in 1922 in a German
scientific 
journal:
Carl Pulfrich: "Die Stereoskopie im Dienst der isochromen und 
heterochromen Photometrie", Die Naturwissenschaften 1922 
vol 10 pp 553-564, 569-574, 596-601, 714-722, 735-743.  

The effect is achieved by any colored or grey filter before
one eye, also by a pinhole for one eye, and even by squeezing
one eye a little and use the eyelashes as filter (I discovered
this about 1985, watching TV and having no filter at hand - 
but I don't recommend it as a practical method :-)).

Indeed several patents have been issued related to the 
Pulfrich effect, but the most simple unpatentable filter will
do.

Abram Klooswyk