Waist level finders: 3d?

[T3D Greg Erker <erker@xxxxxxxxxxxxxx>]

Hi,

  My brother was playing around with my new-old
Bronica S2A SLR. This is a 70's vintage medium format
(6x6) SLR with a waist level finder. Mine has
a 75mm f2.8 lens mounted on it.

  He claimed that the view on the ground glass
looked 3d. And that if you lined up a near and
a far object using one eye and then looked with
the other one you could see that they were no
longer lined up.

  I may have seen the effect. I found it difficult
to judge given the limited DOF of the wide open
lens. It was too dim indoors to stop down the lens
for more DOF. So I'm not sure if it was real or
an illusion of some sort.

  If there really is an effect, I assume it is
from light rays coming through opposite edges
of the lens opening and hitting the ground glass
at the same spot. But the ground glass isn't a
perfect diffuser so you will see the ray that
is aimed towards your eye better than the one
from the opposite side of the lens which is
aimed slightly away.

  If this is true than stopping down the lens
would reduce the effect since the with of
the lens opening is reduced.

So is this possible or is my brother
hallucinating?

Thanks - Greg E.



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