Re: Halo effects (was: Re: Maco IR 4x5)

[Rolland Elliott <liquidriver@xxxxxxxxx>]

...The "halo" effect is due to the lack of an
anti-halation layer.  The light passes through the
film, strikes the back plane, then goes back through
the
film, reexposing it....

I couple of years ago I tried to increase the halo
effect by taping a piece of aluminum foil to the film
pressure plate of an N90s Nikon camera.  I was
surprised to find out that the halo effect did not
increase.

Now I understand why.  When one looks at the film
pressue plate of a Nikon N90s camera through an
infrared camera, the back looks like aluminum foil; it
is highly reflective in the IR spectrum, even though
it is black in the visible spectrum of light. I think
many camera pressure plates have the same reflective
properties, because most other camera pressure plates
I've seen are made out of the same material and are
anodized black.

To increase the halo effect one would likely have to
replace the already reflective pressure plate with
something even more reflective, like a mirror.

Something to try out! Have fun Rolland


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