Re: Converging cameras...

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

>From: LeRoyDDD@xxxxxxx (P3D)
  
>Keystone distortion is the common objection to converging, but my
>opinion is that if keystone is large enough to be objectionable the stereo
>base is far to great, anyway.

>I did some wide-base "rock and run" telephoto shots at NSA Rochester of
>the Kodak building and the sculptures on a couple of the buildings. The
>200-300mm framing and the 20-50ft separation did fine with the subjects, but
>I'm the only one who'll see these.

Aren't these two statements in conflict?  The reason I am asking is that
I have tried shooting architectural details with 135 mm lenses and I could
not do my job without converging the cameras.  Keystoning was obvious
as LeRoy witnessed in the second paragraph.  Yet, I don't think I had
far too great stereo base (given the subject and FL of lenses used) as
he says in the first paragraph.  The point is that long FL lenses and
subject without a lot of depth, need convergence.  This is the case
in high magnification stereos (including SEM) too.

>There's one type of shot that must be converged(so I'm told... I don't
>know what happens when you don't!). A single camera(slr) closeup/macro 
>with edge diffusion(vaseline or special purpose filter).

I'll tell you what happens:  Some parts of the image are diffused in one
frame and not diffused in the other.  The problem is that the filter
is attached to the moving lens.  I was thinking of using a glass with
diffuser (vaseline) so that it is not moving with the lens.  If that's
not possible then one needs to use a small translation (some of these
shots, that I have seen in PSA salons, seem to me totally flat...)

-- George Themelis


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