Re: [APML] RE: Exposure formula. Was: Oh No! Kodak "Improves" Royal Gold

[Roland Roberts <roland@astrofoto.org>]

>>>>> "Bert" == Bert Katzung <katzung1@attbi.com> writes:

    Bert> My problem with 112 minutes is that on ordinary 200 or 400
    Bert> speed film, I would get washed out by sky glow at 112
    Bert> minutes without an LPR filter. I usually go for 60 minutes,
    Bert> even with the filter and stack several. If you have a much
    Bert> darker site, 2 hours might not be all that unreasonable.

Sky conditions are the key.  I know my site and based on what I see
(naked eye) there, I can roughly gauge whether or not an alternate
site will be similar (e.g., when I went to the Summer Star Party in
the Berkshires).

I just discovered today that Michael Covington has a freeware exposure
calculator (for Windows) where you can plug in your numbers.  For
Elite Chrome at f/7 under "dark country skies", it says 2.4 hours.
For "country sky with some glow from town" it says 1.0 hours.

So my rule-of-thumb is really based on both the film and my location.
FWIW, if I shoot from home (NYC) at f/4, it tells me I get only 1
minute.

roland
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Roland B. Roberts, PhD                             RL Enterprises
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