P3D Re: projectors vs. viewers

["Dr. George A. Themelis" <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

I think Peter Davis did a good job summarizing the strengths
and weaknesses of stereo projection vs. viewing in a viewer.

Just a few quick comments:

>The advantages to projecting, vs. viewing, your stereo slides are:
>  
>1) A lot of people can look at the slides at once.

That's definitely the no. one advantage of stereo projection...
Plus, you could try and convince yourself that by the absence
of an optical instrument in front of your eyes (other than the
glasses, but these can be easily ignored...), the "illusion
of reality" (I love this expression!) is stronger... As one
person said in an interview in the Cleveland public radio, the 
impact of a stereo projection is so strong that people have the 
tendency to get up and walk towards the screen, attempting to 
enter into the third dimension... (sounds poetic and slightly
exaggerated to me... :-))

>There are some disadvantages:
>    
>1) Mounting alignment is more critical, so some slides which look 
>   good in a hand viewer may not look good projected.

I hesitate to accept this as a definite fact... I am constantly
seeing mismounted slides in the SSA folios that I participate and
they do bother my eyes as I think they would also do if projected.
Possibly, there is a slightly more tolerance in the viewer but
still not a care-free ride as some people might think.

>2) Color saturation will not be as strong in projection as in a viewer.

Yes, definitely.  The bright white light in a viewer, the full
separation of right and left, the (usually) shorter effective
focal length and clear lenses, will show more details and better
colors.  Projection tends to remove impact from slides, makes them
look dim and details cannot be seen well.  Some pictures might look
better in projection but they achieve that by different means,
like good composition ("through the window" composition is usually
more effective in projection), simplicity, etc.  Stereo projection
is also prone to ghosting that affects images with high contrast.

>3) The impact of the stereo effect will be dependent on the placement
>   of seats.

Yes.  There is a distortion associated with projection when people
do not sit close enough to the screen (which is almost always the
case).  This is known as "stretch".  In this case, the 3rd dimension
appears stretched.  While this "stretch" might benefit some slides,
it almost destroys others, like portraits recorded with normal FL
lenses.  Using longer FL lenses and reduced stereo bases is one way 
to reduce this stretch in special situations.  But with most people
using 35 mm lenses (or even wider) projection can be a bit surprising
for the first time.  (Gradually I believe most people become immune
to this stretch.)
    
>Still, projected stereo slides can be VERY effective, and can be a
>real crowd pleaser.  See if you can find a local stereo club where you
>can actually see some slides projected, to get an idea of the effect.

Good suggestion!  Thanks Peter!

George Themelis


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