[photo-3d] Re: Discovery Channel version of the Loreo

["John Blackwell" <mrmsty@xxxxxxxxxxx>]

--- In photo-3d@xxxxxxxxxxx, "Todd Leghorn" <musclepuppy@xxxx> wrote:
> The Discovery Channel introduced their
> version of the camera last Fall for 
> the holiday shopping season. Well
> before Xmas, many of the retail stores had 
> sold out and they had dozens in each
> store.
<snip>
> I don't think these
> cameras were slow-sellers by any measure, 
<snip>

Well that could be good news.  I hadn't considered that they might be 
carrying the cameras as seasonal items.  That 30%-off sale might have 
been meant to clear space for Summer stock, and they might repeat the 
cycle next year.

> One crucial requirement of using
> Loreo-based cameras is the septum or 
> lenshade. Of all of the variations
> on the Loreo camera, the Discovery 
> Channel camera was the best simply
> because it has a twist-on septum. 
> Early Loreos had no septum, and the
> Argus had a cruddy septum with suction 
> cups that never held for very long.

My camera is an Argus-branded Loreo, but it does have the twist-on 
septum.  The problem is that I forget to put it on half the time. 
The 
result is a lot of accidental ghosting.  (I have photo from Easter 
where a child's face is overlaid with the ghost of a white-framed 
window, and the window doesn't even appear in the image.)

The weird thing about the ghosting, though, is that it comes from the 
opposite side of the camera.  In the example I just mentioned, the 
ghost appears on the left image, but the source of the ghost was more 
than 45 degrees to the right of forward.  I think I might know the 
source of the problem, though.

Consider the following badly-out-of-proportion diagram showing an 
overhead cross section of a Loreo camera:


                                  GHOST
                                  SOURCE

        +----------------------+
        *     glass plate      *
        +----------------------+
         \      --------      /
          \     |######|     /
           \     \####/     /
            \     \##/     / <-- diagonal lines
             \     \/     /      represent mirrors
              \--o----o--/
                 ^    ^
                 lenses

I suspect that the ghosting may have something to do with the glass 
plate that makes up most of the face of the Loreo.  I think maybe the 
light from the GHOST SOURCE is reflecting *internally* on the edges
of 
the glass plate (marked with "*" in my diagram) down to the opposite 
lens.

So, that begs the question: How do you keep a piece of glass from 
reflecting internally?  Black paint?  Roughing up the surface?  Any 
suggestions would be appreciated as I am no expert in optics or 
glassworking.

--John Blackwell


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