[APML] E200 Exposure Times (was: A Rose for Christmas)

["Jon Kolb" <jkolb@datawest.net>]

Robert and all,

> ... I am astonished at how bright the nebula is 
> for just over an hour at nearly F/8.  Criminy!  I would hope 
> my Schmidt would do that deep in that time with E200.  

It seems like I always get a comment or question about the length of my
exposures on E200 when I've posted images lately.  Usually these are of
an "only xx minutes?" variety.  I've always taken that to mean that
everybody else finds my exposure times to be too short to get anything
on E200 with their own setup, and that has me a bit puzzled.  In
thinking about what might be different between my conditions and someone
elses, I've come up with a few things that might account for needing
less exposure time.

1) Altitude.  This is probably the biggest difference between my setup
and somebody else's.  My usual site is at 9000 feet, and some of the
others I've used recently are at 10,500 and 11,000 feet - one of my
favorites is actually at 12,000 feet, but is in a difficult spot and
doesn't get used as much as I'd like.  On the other hand, this Rosette
shot was taken at 7500 feet, a bit lower than usual.

2)Darkness.  Although the light pollution map shows my usual site to be
in the "blue" zone, it doesn't account for altitude, which helps
somewhat.  The Rosette shot was taken in a "black" zone, one of the few
I'm aware of within a day's drive of my home.  Certainly a very dark
site has got to reduce the necessary exposure time, while increasing the
maximum exposure time.  Since the necessary and maximum exposure times
are different at a very dark site, I'd rather just shoot what's going to
work and get more shots done in one night. Besides, the stars will blow
out less on chrome in a shorter exposure.

3)Cold and Dry.  The places I set up at are always cold at night, even
in the summer.  I don't think I've ever seen nighttime low temps above
40F except down in NM or AZ.  It's also usually pretty dry around here
and even drier in the other places I like to go.  I'm not sure how much
that could affect exposure time, but it sure is nice to not need dew
heaters every night.  

4)Reciprocity failure.  E200 seems to just keep recording no matter how
long I shoot.  Once I found an exposure time that works, I tried cutting
it down and pushing the film a stop instead.  That seems to work, too.
All I can say is that the film seems to have very low reciprocity
failure, and that's got to help make the most of any exposure time.

If anyone else has some ideas about this, I'd be interested to hear
them.  And thanks for the nice comment about my image, Robert!

Sincerely,
Jon Kolb
Adventures in Astrophotography
http://home.datawest.net/jkolb/
Life Member, International Dark-Sky Association
jkolb@datawest.net



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