P3D Re: Matched lenses in stereo

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>Recently there has been a discussion in New.3D.Film.Gear@xxxxxxxxxxxxx
>list regarding the tolerances in matching lens focal length (or image
>size) of R and L lenses.  No one seems to have a clear answer of what
>this size tolerance should be.  Ferwerda mentions 1% somewhere
>but only indirectly.  Michael Kaplan suggested using 2x2 projection
>with zoom lenses of identical slides and vary the FL of one slide
>to see at which point the difference in size becomes noticeable and/or
>bothersome.  Then I suggested that we ask camera manufacturers (from
>Realist to RBT) about their tolerances in matching lenses.  Michael
>then asked:

  There are two issues here (IMO) one is
the size missmatch your eyes can handle
and the second is problems from the slide
mount window cutting off the two images
unequally.

  People with unequal eyeglass prescriptions
can see stereo with significantly different
magnifications.

  When I was lens matching for my twin TLR
project (http://www.angelfire.com/ca/erker/twin225.html)
I had a match to 0.34%. But when I mounted these
slides the tops were cut off unequally when
I lined up the bottom (and vice versa). So I
shimmed out one lens by a few thou and got
the missmatch down to 0.13%.  I'm hoping this
will be good enough. (0.34% is about 0.2mm on
a 50mm high image, 0.13% is 0.07mm which is
better than my mounting accuracy).

  So I'd say 1% is way too much due to
the unequal image showing through the mount.
In a windowless system like the LEEP (and
perhaps IMAX) I suspect 1% wouldn't be a problem.

My opinions only - Greg E.