Viewer lighting

["The Photo-3D List" <photo-3d@xxxxxxxxxxxxxxx>]

  Look everybody, a new topic that has nothing to do with using
versus collecting since I'm building my own equipment :)

  I recently built a medium format viewer prototype (King Inn
format mounts).  It uses 1/8" opal plexiglass as a diffuser
located about 1.2" behind the slide. Works great when you have
sunlight or a Luxo type lamp handy.

  I also build an add-on box with a battery powered light. It
uses 2 C-cells and one of George's frosted halogen bulbs
(0.8A at 2.5V).  It works reasonably well except for two
things (three if you count the weight).

  The first is that the illumination is not totally even. The
bulb is centered from side to side, about 1/2" behind the
diffuser and slightly below center vertically. I have a white
reflector behind the bulb in an arc (sort of like my Red
Button). The top and the bottom surfaces are also white. Still
the left of the left eye is brighter than the left of the right
eye, and so on. It's very noticable with no slide in place
and somewhat noticable with a slide.

  The second problem is that it isn't quite as bright as I
would like. Using the spot meter mode of my camera it appears
to be about 1/3 as bright as my Dr. T red button (w/ halogen).
I assume this is due to the diffuser, since with perfect paint
all of the light should come out of the lenses.

  Two C-cells are plenty of weight so I don't want to use any
of the 6 volt bulbs (like the 1A and 1.7A ones George sells).
The 2.5V at 0.8A bulb I have seems to be the brightest 2 cell
one so I am considering using two of these bulbs to increase
brightness.

  I am thinking of having one bulb aligned with each film
chip. The lighting may not be totally even across each image
but corresponding points on each image should have the same
brightness.

Finally the questions:

  What shape should my reflector be? Flat?  Or flat with rounded
corners?  Or should each side have its own parabola reflecter
(assuming the bulbs are equal in brightness)?

   The frosted bulb helps even out the light but there is still
a bright spot on the diffuser where the light comes straight from
the bulb to your eye. I am considering placing a small (bulb sized)
diffuser between the bulb and the main diffuser to even out the
light.

  I know that lighting thru a diffuser like I am doing causes
some problems versus how the red button does it (all reflected light)
but I like my removable light box idea.

  Any thoughts or suggestions welcomed.

Thanks - Greg (no cable tv due to the failure of the Anik E1
satellite) Erker

[Its funny to talk about film "chips" that are over 2" by 2".]




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