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(meteorobs) Meteor photography
Meteor Photography,
>George,
>I was talking with Jurgen about useful films for meteor photography
yesterday.
>He said that he had bad experiences with that TMAX-3200. This film gets
"tired"
>after a few minutes of exposure. The main blackening happens in the first
five
>minutes of the exposure. Hence the limitng magnitude of stars is
appreciable,
>~7.5 or higher when guided, but meteors appearing after that time will not
see a
>high-speed film. This may be the reason of your disappointment about the
>relatively low number of meteors compared to the high sensitivity of the
film.
>Jurgen pointed at the Orion nebula and said that after 30 minutes of guided
>exposure, the nebula should have eaten the surrounding stars whereas the
TMAX
<only shows a slight veil as it can be seen by the naked eye.
>Jurgen noticed this effect of the TMAX by star trails on unguided exposures
>where the trails were always weaker at the end of the exposure than at the
>beginning.
Okay, if you waded thru that first paragraph you all are set to hear my
questions involving films for meteor photography. All films will slow down
quiet a bit due to reciprocity failures during long exposures. but
apparently some of them have more staying power than others. I was slowly
coming to the conclusion that Jurgen pointed out, but didn't comprehend
something until I read the letter from Jurgen and for some reason it fell in
place. But I still have some cloudy areas that needs enlightening. I believe
there are others on this list who are film savvy to know what I'm getting
at? I know during long exposures after about 5 or so minutes, the typical ASA
of film will drop down to the low double or even single digits. For fast
film, they only show their fast characteristics during the first 10 secs
while declining to the low ASA range the longer the exposure gets.
Apparently the film will settle at some ASA equivalent range for exposures
going beyond several minutes. Are there any Black and white films that will
settle on a relatively high ASA range? Or at least higher than others after
the reciprocity drop? Jurgen suggested HP-5. Are there any other films
suggested? How is the staying power of HP-5 or other films up to about 25
minutes? Would totally covering the lens to block the light from entering the
camera for about 30 seconds or a minute recharge the film to the point where
it will take another 5 or so minutes to drop the ASA down again? Thus leaving
the film fast again for this period? The answer to some of these questions
have dual purposes in mind...not necessarily during meteor photographic
efforts.
George Zay
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