P3D Re: Matched lenses in stereo

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>When e.g. the left focal length is 50 mm and the
>right 50.5 mm (1% more), image size is equal when
>both are set at 50.5 mm from the film plane.
>(For simplicity ignoring optical finesses like
>principal planes).
>But, the right lens is focussed for infinity and
>the left for about 5 meter, in this example. This
>is no problem when the lenses are stopped down
>to get a large depth of field.
>(The "Wray Stereographic" exploited this scheme)

  That is how I reduced the image size difference
in my twin TLR from 0.34% to 0.13% (shimmed one
lens out a little further to increase its image
size).
http://www.angelfire.com/ca/erker/twin225.html

>2. The tolerance of the eyes for unequal images is
>often pointed out by quoting the different diopters
>which some people have in their glasses.
>There is however a more simple experiment anyone can do
>now, and Wheatstone was the first to do it, as is
>clear from his 1838 reading.

  Alan Lewis's Freeviewer's Assistant
also works (well) even though the two
eyes are viewing different size images.
Back when this neat product was discussed
someone calculated the image size
difference it produces.
http://members.home.net/3-d/products/products1.htm

Greg E.