Re: Re: The problem with Pulfrich

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

> Bob Wier writes:
>I'd be curious to know if anyone has ever researched whether the effect
>with Pulfrich gives you "real" stereo vision, or something that just
>looks like it?

I'm extremely new to the Pulfrich effect but my limited experience shows
that there are varying effects depending on relative motion. The greater the
degree of motion, the greater the disparity and apparent relative depth. The
effect is true stereo *WHEN it is present* because there is a difference
between the left and right views that the mind is interpreting.

Try watching TV with half a pair of sunglasses. You will occasionally be
treated to startling 3D when the camera pans left or right while following
an actor or with a title placed over a moving scene. While watching sports
there are relatively more opportunities. Some commercials have a lot of
motion but it can be confusing when the motion is in opposing directions or
not horizontal. 

It's interesting that in a stable scene of dialog with almost no motion, you
will notice a flickering kind of effect when someone suddenly moves an arm
or gets up from a seated position. It seems any motion generates the effect
but only horizontal motion produces 3D.

One of the best moments so far was a scenic view of some mountain ranges
from an airplane flying over them. The closer ridges were definitely in
front of more distant ranges. It was a gradual progression that was very
pleasing. I haven't explored the full range of the effect but careful
control of relative rates of motion could be very effective at establishing
lots of depth.

It does tend to have the "cardboard cutout" sensation because the whole of
an object is usually moving at the same rate. It would be very difficult to
create roundness of objects with the Pulfrich effect, unless the objects
themselves were in some precise relative motion too. The scenic view of
mountains did not have the cardboard cutout sensation because the whole
landscape had proportional relative motion.

As to the charlatans out there misadvertising the effect, the best approach
would be an educational one where people are provided with accurate
information so that they laugh at the stupidity of such mis-offerings rather
than spending their money. It definitely helps if they learn about how easy
it is to try the effect if they are curious about it. I was surprised that a
search of  periodicals in the library for Pulfrich effect came up empty.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/


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