[MF3D.FORUM:178] Re: Welcome new MF3D'ers

[Greg Erker <erker@xxxxxxxxxxxxxx>]

>Well, as I understand it, there are variances between identical lenses for
>the SAME style camera, so the likelyhood that there would be noticeable
>differences between the two different BRANDS of 75mm lenses is
>a real possibility.  Also, the distances may vary somewhat between the
>lenses and each camera body's film plane. This would result in possible
>different scaled images.  It seems that All of this together could be either
>insignificant or quite noticeable.  I would be willing to guess that two
>identical brand models would be the way to go for the twin images.

  You are right about the lens FL's likely
being different. But if they are both the
same FL then the second principal point (is
that the right term?) will be 75mm from
the film plane if both lenses are focused at
infinity.

  From my understanding of John B's perspective
paper the entrance pupil (primary principal
point?) controls the perspective seen by that
lens. Thus a 6 element lens would likely have
this point further from the film plane than
a 4 element one (assuming the Rolleiflex has
a Tessar say).

  If I understand this correctly, you would want
to line up the two entrance pupils side by side
rather than have the two film planes exactly in
line. If you did the former then the image sizes
and perspective (excluding the 3d parallax you want)
will be the same for the two cameras (assuming
lens FLs match).

Greg E. (speaking at the very boundary of my
knowledge :)