[photo-3d] Stereo Dissolve- problem?

[Peter Abrahams <telscope@xxxxxxxxxx>]

>stereo dissolve  It can be fun or instructional.  A nice effect to have

It certainly is a nice effect to have in the arsenal.  When I showed my
stereo x-rays of seashells, it would have been fantastic to slowly dissolve
a color slide of the shell into the x-ray.  Other very effective uses would
be a before & after sequence, or a child growing up, or a sequence of
sports photos.   My problems are when it is used for all presentations.  I
think the dissolve needs to be factored into the planning of the slide
sequence.

When viewing a sequence of stereo slides, one can feel the eyes move in
convergence or divergence.  If all are accurately mounted 'to the window',
this is minimized.  But even if the slides were all precisely mounted to
the window, the center of interest or main subject of the photo isn't
necessarily at the window -- for example, in an image of a building across
the street, the near point of the foreground -the street- has to go at the
window.  If the next slide were an interior of the building, mounted to the
window, the eyes would likely diverge.  If use of dissolve means that both
photos are on the screen at the same time, there is a moment of major
stress to the eyes (at least I find this to be so; and I'm sure many others
do; and I'm sure that mounting slides for projection means that you have to
accomodate your audience to some degree).
Even properly mounted slides, in sequence, force the eyes to converge &
diverge.  When there are two images on the screen with varying requirements
for convergence, I get a headache.  Having experienced this many times, I
just close my eyes momentarily......and if this continues, I just close my
eyes until the show is over!  
During long slide shows, like at NSA, I think it would be much easier on
the audience if dissolve were only used at the request of the photographer.
I think that a photographer needs to keep these concerns in mind when
planning a sequence:  ensure that when two image pairs are on the screen
simultaneously, the R-L image pairs of major subjects of interest are the
same distance apart.
One final note about dissolvers.....the Brackett dissolvers in use at the
NSA in  Bellevue put a loud hum or buzz into the sound system during
dissolves (a rheostat or whatever will do this).  For most shows, which
used rock & roll or some such noise, you wouldn't notice; but I used a Bach
organ piece that certainly suffered from the intrusion.    --Peter
_______________________________________
Peter Abrahams   telscope@xxxxxxxxxx   The history of the telescope & 
   the binocular:   http://www.europa.com/~telscope/binotele.htm