P3D Re: On the "why the 1/30 rule does not work"

[Tom Deering <tmd@xxxxxxxxxxx>]

George said:

>I am not playing a game with words here.  Some beginners might really
>think that 1.2 mm on-film deviation is some kind of optimum and go
>for that.  Well, I have news for them:  It is not!  For me personally,
>1.2 mm OFD in a close-up is a bit too much.  And I have mentioned that
>I have seen PSA winners with near zero OFD.  And many people have
>recorded stereo pairs with more than 1.2 mm OFD and they have survived
>(the audience too!)

I do appreciate George's comments.  Based on his words, I've added
additional material to http://www.deering.org/basis.html including a
reference to Bercovitz's formula.  I found this concept difficult to grasp
myself until I started building my own camera.  Until then it was all
theory--intangible.  When you start drawing the triangles for yourself, the
geometry becomes real.

OFD is a physical measurment "on the film" of the mechanical limitations of
*your* eyeballs, occular muscles, and brain.  Different eyeballs, different
OFDs.  I left this out of my explanation for clarity, along with a lot of
other stuff.

1.2 mm OFD is comfortable to view for most people (35mm).  Choose a bit
more or a bit less to suit your tastes.  Once you've done that, you've
defined the *maximum* stereo information that your two images can hold.
This is  key to understanding the limitation of the three dimensional space
in your photos.

No one can say what "optimum" stereo is for any given scene.  As George
says, some prize-winning photos are practically flat.  No theory or formula
can tell you how much stereo to put in a photo.  The formulas can only
predict the limits, the maximum that is viewable.

Whether you use all of that maximum is up to you.  But you can't stay
within the maximum if you don't know what it is. And you certainly won't
find out using the 1:30 rule-of-thumb for macros.

Tom



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