[photo-3d] Pulfrich pseudo & history & web refs

[Abram Klooswyk <abram.klooswyk@xxxxxx>]

Mark Dottle 29 Oct 2000:  (...)
>.... and of course there is no "pseudo" effect experienced. 

In fact there _can_ a pseudoscopic effect! 

I have written on "A PULFRICH 3-D HISTORY" in Stereo World
jan/feb 
1989 vol 15 No 6 pp 14,15,27. A few excerpts:
>>
As early as 1965 W.C.Dalgoutte, the famous editor of the
British 
Stereoscopic Society Bulletin, wrote on the 3-D effects in
ordinary TV 
programs when watching them with a filter before ONE eye - an
effect 
comparable to the old chrono stereo effect which displaces
moving 
objects when the single views of a stereo pair are made
sequentially. 
Dalgoutte used a pair of polarizing filters and rotated them
one 
across the other until a substantial loss of light was
achieved.  
(...)
Tokyo Movie Shinsha Company made "Remi", a "Three-Dimensional 
Animation" series in color of no less than 51 episodes of 30
minutes 
each. Movements where designed to give a Pulfrich 3-D effect
when a 
filter was placed over the left eye. The story was based on
the famous 
international children's classic "Nobody's Boy", written in
1878 by 
Hector Malot. This series was broadcast in Japan in 1978. It
seems 
that some 10 million "Pulfrich glasses" with a neutral grey
filter on 
the left and a clear acetate on the right were distributed in
Japan 
for that series. 
(...)
....the only country in Europe where it was broadcast seems to
have 
been the Netherlands. The episodes were on Dutch TV screens
twice a 
week from October 1979 to well in the year 1980. The Pulfrich
glasses 
were supplied from Japan, and were distributed free with
"Prodent", a 
toothpaste brand. About a million glasses were made for the 
Netherlands, which covered almost all Dutch children of the 
appropriate age group. (...)

The story is appropriate to a lot of moving scenes, for the
boy Remi 
is a supposed orphan traveling through France with a group of 
entertainers. Generally about one third of an episode showed
the 3-D 
effect, for obviously not all movie scenes could have
horizontal 
movements. 

  As John Dennis reported on the Nuoptix demonstration (Stereo
World 
Sept./Oct. 1988, p.2) movements in the opposite direction
cause 
pseudoscopic disturbances. This was especially the case when
the 
traveling group was visible moving through the landscape,
apparently 
followed by the camera. Although closer than the background,
they 
moved to the RIGHT, which displaced them farther back than the 
background. This effect was fairly evident to me, but as John
Dennis 
correctly supposes, few in the general public seem to notice 
pseudoscopy before you ask  them, and even then some never get
the 
point.  <<

Sofar for the quotes. There is a lot on the Pulfrich effect on
the 
net nowadays. 
Gabriel Jacob 29 Oct 2000: 
>Actually the easiest way to demonstrate the pulfrich effect is right 
>there in your hand! Just move your mouse! 

But on my system the cursor moves somewhat jerky... :-) 
Check out some java demonstrations. Swinging pendulum in java
at:
http://www.bu.edu/smec/lite/perception/pulfrich/exp.html
and Mark Newbold's java applet at:
http://dogfeathers.com/java/pulfrich.html

A still of a classical pendulum demonstration apparatus is at:
http://jedlik.phy.bme.hu/~hartlein/physics.umd.edu/deptinfo/facilities/lecdem/o2-11.htm

(Of course even now we don't always have to look at computer
screens, 
hanging a real object at a real string 2 or 3 feet long still
can be 
done :-))
In the Pulfrich effect there are at least 3 variables:
"pendulum" 
speed, filter density and viewing distance. All three affect
experienced depth.

To go deeper in the subject check the "Pulfrich Homepage":
http://www.siu.edu/pulfrich/index.html
There you find several original papers, including Christianson
& 
Hofstetter's "Some Historical Notes on Carl Pulfrich" and even 
Pulfrich's original 1922 papers (in German, PDF of
photocopies).

Abram Klooswyk