Re: (Fwd) Re: I guess I'll do it, too.

[boblong@xxxxxxxxxxx (Robert Long)]

On Fri, 06 Dec 1996 19:49:39 +0000 (GMT), John Sparks wrote:

|Light piping works by total internal reflection (look this up in a
|physics book if you are interested).  None of the lightpiped through
|the film leaves the plastic film base so it would never get a chance to
|be absorbed by the backing.

Umm...  I assume you didn't mean this passage to be taken as literally
as I did at first.  If *none* of it leaves the film base, it couldn't
fog the emulsion and therefore would be no problem.  Presumably 100%
of what goes into the leader end would be transmitted the lengths of
the film and exit at the tail end (or along the edges) and be absorbed
into the plastic spool within the cassette.

The percentage of the light that escapes from the Estar into the
emulsion may be very small, however.  Even in subdued light with rapid
loading, the total light (visible and IR) to which the leader is
subjected is vastly larger than that used in making an exposure
through heavy filtration.

Bob Long
(boblong@xxxxxxxxxxx)

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Topic No. 12