P3D Re: 3D Movies and the 1 to 30 rule

[Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Fri, 03 Apr 1998 
>From: Jonathan Gross  Writes:
>......
>I would like to point out that the 1 to 30 rule is only valid under the
>following conditions:
>
>1.  The focal length of the lenses are about 35mm
>2.  The film (or imaging element) is 24mm high
>3.  The image separation at infinity (delta) is 1.2mm 
>
>If any of these conditions do not hold, then the 1:30 rule does not
>work, although there are other combinations of image size, delta, and
>focal lenght which also yield a 1:30 ratio. When using 35mm SLR cameras,
>for example, here are the calculated ratios for a delta of 1.2mm:
>
>Lens Focal Length     Ratio of Lens Base to Stereo Window
>	24mm			1:20
>	35mm			1:30
>	50mm			1:42
>	100mm			1:83
>
>This explains why the standard 1:30 rule works for Realist cameras, but
>not for SLR's with standard 50mm lenses; for 50mm lenses the ratio is 1
>to 42, and not 1 to 30, a 40% greater seperation.

*****   I'm sorry to disagree here but this list of numbers seems oddly
reversed. 1:42 is 30% LESS interocular separation than 1:30, so the entire
list above would seem to be going in the opposite direction from what is
needed for the relative lens lengths. The combination of 100mm lens with a
ratio of 1:83 would end up almost FLAT. Perhaps it was calculated from the
wrong formula?

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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