P3D Mike Waters

["Lawrence A. Haines" <lhaines@xxxxxxxxxxxxxx>]

Michael Waters:

Forgive me for bringing up an old subject again.  Perhaps you will
remember the
message you sent to photo-3d last February relative to base separation
for twinned stereo cameras.  You developed a simplified equation which
read:

B (Base Separation) = S1 (distance to nearest object) / f (focal length
of lens).

I have some questions.

1.  I assume that in some way I do not fully understand, the equation
gives a "good" stereo effect (however one would define "good").
Apparently this is established in having the maximum deviation on the
chips about 1.2 (simplified to 1).  Deviation I assume is the maximum
distance apart of the closest parts of the picture.  I have heard
somewhere
that this is the most comfortable to view - which I guess could define
"good".   Is it true that this value was established by trial and error
of a
number of stereo photographers?  Or, is there some kind of physical
relationship I am not aware of?

2.  If I were using 28 mm lenses and the nearest object were magically
28
feet away then the cameras should have a base separation of one foot -
correct?  Or if the distance of the nearest object was 280 feet the base

should be ten feet - correct?  Looking for the edge of the envelope let
me
ask, what happens when the nearest object is about a half a mile, say
2800 feet.  This would seem to indicate a base of 100 feet. But I guess
there is some practical limitation for a particular focal length lens -
is that so?
This does not seem to be incorporated in the equation.

3.  Then if I am using 135 mm lenses, the oft spoken 30/1 rule is really

wrong ( as you point out) since it should become rather 135/1 - right?
So a camera base of one foot would be correct for nearest distances of
about 135 feet - right?  This is quite a bit different than the 30 feet
to the nearest object suggested by the 30/1 rule.  I would ask
your indulgence for my poor mind but I am anxious to get it right.
Using the long focal length lenses for things far away would therefore
seem to enhance the stereo, and should be used for long distance
applications.  If I wanted to put clouds in stereo, I might seek even
longer focal length lenses?

4.  I have spoken to a stereo photographer who takes a lot of twinned
camera pictures.  He suggests that I carefully record what I do on
each shot since the actual results might dictate something different
than the
equations.  I am not yet ready to accept this, since it does seem to me
that these equations are pointing at defining optimum results.  I would
like your comments on this.

5.  The matter of the perceived diminuation of the objects in the
picture
is of concern to me also, but this equation does not seem to address
these
things at all.  Do you know of  a mathematical relationship that defines

this elusive characteristic of some wide base photos?

If I am being to much trouble please just ignore these dumb questions.

Larry Haines
P.O. Box 1177
Eastsound, WA 98245
tel 360-376-4704
e-mail <lhaines@xxxxxxxxxxxxxx>




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