Re: [photo-3d] RE: Depth ranges

[Paul Talbot <list_post@xxxxxxxxx>]

"David W. Kesner" wrote:

> I am forced to use a "fixed" setup with the RBT Macro and was
> just wondering if there was anyway to reduce this problem.

Limit your near point!

> Is there anyone out there that can do the math and tell me

No need to have someone do it for you.  You can go to Tom
Deering's site and use his spreadsheets:
http://www.deering.org/math/spreadsheets.html

Because you have a "fixed base" camera, use the fixed base
spreadsheet.

> the maximum near and farpoints are for this setup assuming a
> 1.2mm mofd?

The near point depends on the far point (or vice versa).

Once the far point is distant enough, the minimum near-point
will simplify to 30 times the stereo base.  So 11mm times
30 is 330mm, or about 13 inches, as Chuck Holzner pointed
out on 16 Feb.

When you get down into these close working distances, the near
point becomes very critical.  You said the near point was less
than a foot, but we must know "how much less."  If you use the
variable base spreadsheet on Tom's site, you can see that
cutting the near point from 13 inches to 6 inches, (with a
far point at "infinity") the stereo base has to drop from
0.4 inches to 0.1 inches.  0.3 inches is a small number, but
that's slashing the stereobase by 75%!

> Once again it uses a 105mm lens on a bellows that magnifies 
> from approximately 1:3 to 1:1. 

I've never worked with a bellows, but my guess is that if
you use different magnification you are getting a different
effective focal length on the lens.  I think you should run
the calcs with the effective FL of the lens.  (With many near
and far point combinations, the result is not very sensitive
to changes in the FL variable.)

For a great review of stereo base theory, here is a link to a
post by Abram Klooswyk dated 15 Aug 1998:
http://www.pauck.de/archive/mailinglist/photo-3d/mhonarc/msg27625.html

Paul Talbot

 

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