P3D Re: What is the "Stereo-Base"?

[fj834@xxxxxxxxxxxxxxxxxxxxx (Dr. George A. Themelis)]

>*Rubbish* - Those answers is good for amateurs!

I am an amateur and darn proud of it!  Are you a professional?

I can remeber the formula you posted as the FBI rule (we can all
remember FBI, can we?), so:

Parallax =  F * B / I  (where F the Focal length, B the stereo Base and
                        I the distance)

>A. What "parallax" is?

Another term for it is "on film deviation" or OFD.  In stereoscopic
photography two objects at different depths photographed from different
angles (as by shifting the camera) will give two projections in the film
that are not of equal distance.  This difference is the OFD.  When you
view a stereo pair this OFD (however it was created) converts to depth.
This is a fundamental concept in stereo.  Everyone in P3d should be
aware of what this term means... but more deep discussions or formulas,
etc. should be directed to tech-3d (see instructions at the end).

>B. Here in Israel we use the "Metric System"
>    How can I use the formula only meters & cm?

Yes.  If you put the FL and distance in mm then you will get the answer
(parallax) in mm.

>C. I know the near point, and I want to calculate
>   the "base-line" - How can I do that?

You can use 1.2 mm for parallax and see what stereo base you get.
1.2 mm is generally accepted (but not etched on stone by any means)
as the maximum OFD that will allow you comfortable stereo viewing.
You can use less than this if you want or more if you know what you
are doing.

If the far point is at infinity then you use this formula.  If the far
point is not at infinity then you need to subtract the two values, i.e.
use this formula:

Parallax = F * B (1/Imin - 1/Imax)

(at infinity the second term becomes zero)

Please direct further mathematical discussion on this to tech-3d.
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Regards from Cleveland OH,  George Themelis


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