Re: [photo-3d] Slide projection

["John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>]

This (scene to scene transitions) is not much different from the problem of
cutting one scene to another when editing a stereoscopic (3-D) motion
picture.  Few producers or directors seem to recognize the importance of
maintaining parallax range at edit points.

Actually there is little difference as to ease of viewing as to whether a
transition is a dissolve, a wipe, or a crash cut.  This is true whether we
are changing slides or changing scenes in a motion picture.

The real key is matching scenes so that there is not a rapid change at the
cut or slide change point.

This means that in addition to story line and continuity, you should also
pay attention to what follows what in terms of depth range - whether you are
editing a motion picture or editing the assembly of a slide show.

What do you watch out for?   Radical differences in either negative (front)
or positive (rear) parallax from one scene to the next, or one slide to the
next.

For example, you would want to avoid cutting a film or editing a slide show
such that one scene with everything in the scene were in negative parallax
(theater space or audience space) directly to one where everything were in
positive parallax (behind the screen).   Or, vice versa.

This causes the eye muscles to have to make a rather radical adjustment,
which may not be noticed right away, but will result in eyestrain and
possibly even headaches.  The headache may not come immediately, but perhaps
an hour or so after the screening.

There are several editing procedures that can be used to avoid such an
uncomfortable situation.

The best is to plan the editing before the original photography.

If this hasn't been done, and there is sufficient material, the next best
technique is to insert another scene, event, or slide in-between that is
also in-between in parallax, perhaps a scene that has little depth range
(where most objects are near the screen plane), or, better yet, a slide or
scene that has elements in both negative and positive parallax.

This will lead us more gradually from the first situation to the second, and
allows the eyes time to accommodate to the different set of conditions.

If this is done, the transition will be much more comfortable to view,
regardless of the type of transition.

This should not infer that you cannot cut a closeup to a long shot or a
hyperstereo to a hypostereo.  As long as the parallaxes are similar, these
should pose few visual problems (esthetics aside).  But, it does mean that
you must watch out for radical
positive-to-negative (and the reverse) parallax jumps on adjacent slides or
cuts.

The editing of stereoscopic material is much more important than it is
usually given credit for, and will definitely affect how comfortable the
material is to view.

JR

----- Original Message -----
From: <dougorama@xxxxxxx>
To: <photo-3d@xxxxxxxxxxx>
Sent: Thursday, October 12, 2000 2:15 PM
Subject: [photo-3d] Slide projection


> As a neophyte 3d'r, I am concerned about these headaches, nausea and
> whatnot asc w/ viewing 3d images. Presuming the slides are mounted
>  "perfectly," which of the following would be LEAST jarring to the
> audience?:
> 1) Dissolve between two 3d images
> 2) Fade to black, then fade in next image
> 3) One image to next, with quick black transition between{such as a
>    one projector 2d show}
>
> Also... would a practical limit for viewing be about 20-30 minutes?
> Slide projection is a must: Viewers are impractical for my purposes.
>
>
>
>
>
>