Re: [photo-3d] Re: Newbie question-near point distance

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

----- Original Message -----
From: "Dr. George A. Themelis" <drt-3d@xxxxxxx>
To: <photo-3d@xxxxxxxxxxxxxxx>
Sent: Saturday, April 28, 2001 9:59 AM
Subject: Re: [photo-3d] Re: Newbie question-near point distance


> >Hi George!
>
> Hi Mike!
>
> [long snip]
>
> >So which do you prefer for dealing with a change in focal length?
> >David Lee's method or McKay's PePax rule (Wednesday or Friday)?

This is a good example of where practical results outweigh mathematical
precision.  My answer is that it is very subjective.  Stereo photography
itself is very subjective.

I use stereo bases from very narrow (5mm) for ultra-macros to very wide
(several miles for high altitude aerials).  The macro stereo lens with the
5mm interaxial is 12.5mm in focal length.  The lenses I use for aerial work
range from 50mm to 500mm in focal length.  I also have a dual camcorder rig
with fixed interaxial, adjustable convergence, and zoom lenses.  At some
point in the zoom range the result is probably ortho.  Exactly where does
not matter for the purposes for which I use it, since the results are
usually very pleasing at both ends of the zoom range (12mm to 96mm).  When I
can vary the stereo base, my choice of interaxial distance is determined
more by the characteristics of the subject than any particular formula.

Years ago I used to consult numerous tables and formulae (I have a bookcase
full of books on stereoscopy) including McKay's.   They tended to disagree
with each other, and more importantly, not always relate to the real world
of practical stereo photography.  Now, I just shoot on intuition based on
experience.  In stereo photography, experience is the very best teacher.
Using this approach, I know when to narrow or widen the baseline, because I
can now have a pretty good idea of what the results will look like before
the shot is made.  If an element is changed in the scene, such as a change
in the near point, the far point, depth references, etc., I will alter the
stereo base and/or convergence as required to optimize the final parallaxes
to the subject.

JR



 

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