Re: [photo-3d] The Stereoscopic Society Annual Competitrion

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

----- Original Message -----
From: "William Gartin" <william_gartin@xxxxxxx>
To: <photo-3d@xxxxxxxxxxxxxxx>
Sent: Wednesday, February 14, 2001 10:42 PM
Subject: Re: [photo-3d] The Stereoscopic Society Annual Competitrion


> on 2/15/01 12:22 AM, John A. Rupkalvis wrote:
>
> > No.  The optimum separation angle (and the resulting parallax) are
variables
> > that cannot be quantified for all subjects.  Each subject is different,
and
> > several factors enter into the judgment as to what is best for a
specific
> > stereo image.  Things such as contrast, color, association, sharpness,
> > relationship of other objects in the image, etc., etc., all must be
> > considered in the evaluation of the most appropriate settings.  Even
whether
> > convergence is parallel (shift lenses or shift mounts) or toed in.
> > <snip>
>
> Okay, now you've gone and made my brain hurt! Maybe I should stick to
> Hypers. ;-)
>
> Next question: photographing an insect, macro, with a very shallow depth
of
> field and, say, a distant background of shrubbery. If the background is
this
> out of focus, would the individual angles of view of the subject be the
only
> concern in determining the base for depth perception? Or is there still
> enough depth information in the out of focus areas to be useful? Also, in
> cases like this, is it better to toe in to keep the subject dead center
for
> each view? I'm guessing less or no toe in IF the background is important,
> but yes if it's not.
>  --
> William Gartin <william_gartin@xxxxxxx>

A good example.  Shrubbery tends to be homogenous in terms of the ability to
"lock the eyes" to the background, and would likely be less of a problem
than something with strong verticals or geometric patterns.  A brick wall,
telephone poles, picket fences, etc. in the background would likely cause
problems even if considerably out of focus.

Of course, being out of focus in itself can cause visual problems, and for
some people even eyestrain (as the eyes try to focus on what is essentially
"unfocusable").   Usually, a stereoscopic image is best if everything in the
image is sharp.  There are, as with most things, exceptions.  For example,
if the background is not in itself definable (a blue sky, for instance), or
is disguised in something else (such as motion blur).  An example of motion
blur in still photography would be when you pan or otherwise move the camera
to follow the subject and keep the subject sharp, like an image of an
athlete running.

The amount of convergence is really a judgment call depending upon all of
the characteristics of the subject, including the background.  Keep in mind
that it is much easier to toe the eyes in than out.  Therefore, if the
background is definable, it will tend to cause eyestrain and possibly
"split" before the foreground.  In most instances you will not want to
converge on either the subject or the background, but somewhere in-between,
that position being a compromise determined by how much parallax you want to
allow for either.

Also, you must consider the composition; the amount of the frame taken up by
the subject.  If the subject is a small part of the total scene, you will be
mainly concerned with problems with the background (and, in this instance,
the background must be sharp).  If the subject is large and/or close, such
that parts of the subject are occluded by the frame edges, you must consider
the stereo window, the stereo pyramid, and whether any background still is
visible.
In general, you will find that when doing macro work, it is often easier to
limit the background (such as through camera angle) so that it is not so far
away as to cause problems.  Otherwise, you must either use shorter focal
length lenses and/or a narrow stereo base.

There is much more to this than what could be discussed here.  Entire books
have been written on the subject of flat macro photography, and stereoscopic
macro photography involves all of this plus much more.  I still feel that
you can learn the most by doing it.  You will, through experience, learn
what works best under what circumstances, and why.

JR