Re: [photo-3d] Camera separation in stereo photography

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>>Back to basics 101 -- I believe that the 1:30 rule only applies
>>when using 35 mm lenses Don.
>
>  I believe it applies any time the viewing
>FL matches the taking FL.
>
>  I wish John B. were here to make sure
>I'm not spreading errors, but I'm pretty
>sure I understand this correctly.  If Tom
>or George and anyone else wants to correct
>me feel free.

  I just did some playing with the MAOFD
spreadsheet that John B. created.  The
comments say:
     "Bercovitz & Spicer's formula to limit
      maximum on-film deviation by limiting
      stereobase.
      The on-film deviation should not exceed
      one thirtieth of the focal length of the
      stereo system.
      The effective focal length of the camera
      lens should match the stereoviewer's focal
      length."

  So if I use a 35mm lens the desired OFD is 1.17mm
(35/30). If I use 7' (2.13 metres) as the near distance
and infinity (999 metres) as the far, the spreadsheet
says the "maximum allowable stereobase" is 70.4mm.
Just like a Realist. (Note: this is assuming I am
viewing with a 35mm viewer lens which most of us
don't have).

  For a Sputnik the lens is 75mm so the desired OFD
is 2.5 mm. If I use the same near and far distances
the spreadsheet gives the max stereobase as 69.9 mm.
Basically the same as the Realist case. (Note: this
assumes I am viewing with 75mm lenses).

  Both of these match the 1:30 rule. 30 times 70mm
= 2.1m which is 7'.

  BUT: if you change my taking FL without changing my
viewing FL then you get different results.  If I shoot
with a 135mm lens and still view with the 35mm lens
my OFD remains at 1.17mm but now the spreadsheet
gives a max stereobase of 17mm, for the same 7' to
infinity shot.

  Shooting with a 24mm wide angle lens with the same
near and far (but still viewing with 35mm) gives
max stereobase of 177 mm.

My understanding (and I'm willing to be corrected) - Greg E.