Re: ghosting (Seashells)

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Sat, 26 Jul 1997
>From: P3D Peter Abrahams writes:
>.........................
>When I noticed the obvious ghosting during the projection, I did not
>dismiss film depolarization by any means, but investigated it at some
>length, ......................... I believe that more complete extinction
>could be achieved with a sandwiched polaroid. ..........................
>Regardless, it is a fact that crossed polars will transmit a small
>percentage of light, one percent .......... This effect alone is
>sufficient to explain the ghosting in the x-rays.
>
>It is possible that these slides are not suitable for projection.  I
>purposely sought high contrast at every stage of the project, but may
>have eliminated sharing them with a group as a result (until those
>electronic goggles are more ubiquitous).

******  I have to add a comment here about the Seashells as projected at
NSA. I was aware of a small amount of ghosting and aware that another
problem was more contributory to these images being difficult to view.
(relatively speaking) They were still enjoyable shots and very beautiful! 

The images had a relatively high percentage of areas that weren't expressed
equally in both left and right views. This created a bit of rivalry in
certain parts of the images. This sense of trying to see something not
there, heigthened any effect the ghosting might have had, while the ghosting
seems to be getting all the blame.

I verified this during the projection by examining each eyes' view
separately. The differences are minor, but strong enough to be felt in
several of the images. These errors can be fixed in PhotoShop if you want to
improve on the already good material.

As to the polarization problem, why not try the simple expedient of taping
additional polarizers to the end of the projection lens and see if there was
a difference. If so, then the film polarization was present. If there is no
difference, then it wasn't the film. I suppose the problem really boiled
down to the projectors were too well used to allow for experimentation time.  

I enjoyed the Seashells and all the projected shows. :-)



Larry Berlin

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


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