T3D inverse apodizer

[John Toeppen <toeppen@xxxxxxxx>]

A black spot fading to gray on the edges in produced by firms like
Reynard Optics to compensate for vingetting ( the fall off in
brightness  from the center to edge of the image).  This trick was first
used for ariel recon lenses in the 40s and a big gray fuzzy spot was on
the lens axis.  These large lenses produced images that were also not
distorted in the film plane when the lens was used to view objects at a
distance.

These apodizers are vacuum deposited inconel on glass.  The spot size
and gradient density need to be a pretty good match for your lens
(pinhole).  Ideally, the camera would be looking into a white
integrating sphere when you scanned the intensity of the light in the
film plane. Then you would calculate the optical density for each zone
if you placed the "gaussian" apodizer in a specific location either
within or behind the lens.  Then you would need to specify the vacuum
deposited inconel density.

The photographic technique has you photographing a piece of uniformly
illuminated white paper in sunlight, intentionally working out of
focus.  Bracket some exposures from 1 stop over to 5 stops over
exposed.  Process the negative to achieve a gamma of 1 to produce a
linear apodizer.  If you do not have a free guide from Kodak on how to
process scientific films and plates ask Kodak, look it up, or just
develop for 80% of the recommeded time (this is part of the reason why
you overexpose) 

This apodizer would best be installed in a 4x5" film pack in contact
with the unexposed film.  A bellows camera would allow you to make the
exposure of the apodizer right behind the lens where you would later
mount it. The quality of the film transparency will affect the image
quality if it is not in contact with the film.  The Estar base and
emulsion of TechPan is five to seven waves in transmission.

Good luck.

John Toeppen
http://members.home.net/toeppen/


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End of TECH-3D Digest 481
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