P3D Re: Mounting Standards and Projection

[fj834@xxxxxxxxxxxxxxxxxxxxx (Dr. George A. Themelis)]

>Brenda N., following an enjoyable evening of 3D at a PSSP meeting, said:

>"After the first show (these were slides taken by PSSP members) Mr. Duggin
>tried to explain the importance of mounting properly and consistantly by
>standards set for stereo photography.  He threatened that in the future
>there would be no more adjusting of the projector.  

Amen!  I am a member of two clubs (Detroit and Cleveland) who's policy is
not to adjust the projector between slides.  IT WORKS.  That's not a
threat.  It is a reality.  In Detroit we can have 90 slides in one night
from 30 members, many of them beginners.  We do not have any serious
problems with alignments.  

If the images are a bit off then more harm is caused by trying to align
them than leaving them as-is.

>Either mount properly by set standards or suffer the consequences.  

The consequences are that the slides will not look at their best.  Sounds
like a fair treatment.

>A few members argued that you could
>not be consistant because viewing situations vary.  For example one person
>said that if you mount to project in your living room the same slide would
>not work for a larger room where the projector would be farther away.
>Someone else said the size of the screen would make a difference."

It is only the size of the images that could make a difference (this is
obviously related to the size of the screen) but, as LeRoy said, what
counts for vertical misalignment is the size of the image seen and in large
projected images people tend to sit further from the screen (except of
course for the ortho-fanatics), which reduces the effect of the errors. 
Infinity separation is a bit different (but not very much) and some caution
and conservatism to avoid excessive parallax is suggested.  With this
caution in mind, images that look well projected at home, should look well
projected in a larger screen.

LeRoy writes:

>    Modern precision mounting materials make good verticals
>automatic (almost) if the film chips come from a "real" stereo camera. 

That's correct.  There is really no good excuse for poor mounting.

>    3) Incredibly, the projectionist may have corrected bad verticals in
>the slide just before yours and your perfectly aligned slide is now
>projected out of alignment!

That's the best argument against adjusting the projector during the show. 
It can punish those who do a careful mounting job to benefit those who
don't.  The first seconds that the image is projected have the most impact
for the judges and audience.  It is a pity if these precious seconds are
spent in adjusting the chips and torturing everybody's eyeballs.

George Themelis


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