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Re: (meteorobs) Meteor photography



In a message dated 96-06-14 14:40:29 EDT, Marc de Lignie wrote:

>ding the reciprocity failure of B/W films: I always thought that this
>occurred for a constant 
>illumination. So, a short exposure by a bright light source (meteor) should
>not be influenced very 
>much by a long pre-exposure of weak stray light.
---------

This has always been my belief also, but Jurgen has pointed out that the TMax
-3200 films appeared tired to respond to meteors after being exposed for
about several minutes of dim illuminations. I too have been thinking along
these lines. I've probably exposed about 1000 hours using Tmax 3200...but I
used D-76 and that may be some of the problem.  I can't explain the
reasoning, but it just appears to be doing that. Perhaps the dim
illuminations produce a thin barrier of "exposed" film that won't allow the
light of  meteors to fully respond as it would normally do if the meteor
occured during the first several minutes? The end result is that it needs
more brighter meteors to overpower the "barrier"...And then they don't appear
as bright as expected.  I know that when certain metals rust, the rate of
rusting slows down because of the layer of rust built up on top slows down
the rate of oxygen available to continue the rusting process at the surface
of the non rusted metal.   I'm not saying here that the film is rusting, but
only using it as an analogy to describe something similar that may be
happening...but with light.  Anyhow, I've switched to HP-5 as a precaution
and will most likely start using T-Max developer.  I'll see how that works.
George Z.