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

["Bert Katzung" <katzung1@attbi.com>]

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

Bert Katzung
katzung1@attbi.com
www.astronomy-images.com

----- Original Message -----
From: "Roland Roberts" <roland@astrofoto.org>
To: <astro-photo@seds.org>
Sent: Thursday, August 22, 2002 2:41 PM
Subject: Re: [APML] RE: Exposure formula. Was: Oh No! Kodak "Improves" Royal
Gold


> >>>>> "Bert" == Bert Katzung <katzung1@attbi.com> writes:
>
>     Bert> How does your rule of thumb formula work for slower scopes?
>     Bert> For f/7 it seems a bit on the long side: 14 x 8 = 112
>     Bert> minutes? I assume this is _without_ an LPR filter?
>
> Yes, it is without an LPR filter.  FWIW, my rule-of-thumb is not much
> different than others I've read, e.g., the f^2 rule.  And while it
> does seem rather slow, I can say that the one shot I took at f/8 for
> 20 minutes was way underexposed.
>
> My shots last month (30 minutes at f/2.8) may be a little on the long
> side for the site; they are definitely lighter than I expected, but I
> do not think they are too far wrong.  Even so, you can do okay within
> a factor of 2 on the exposure.  The f^2 rule would indicate 49
> minutes; I tend to think twice that long is fine provided the skies
> are dark.  With an LPR filter you can also go longer without
> increasing the sky fog.
>
> I'm new enough at this and haven't yet tried enough different
> exposures to know for sure.  Perhaps next month I will try some longer
> exposures; I have a couple of telephotos (135mm and 200mm) that will
> need to be stopped down to at least f/5.6 and maybe f/8, so I'll have
> to try a few long exposures to find out.
>
> What I really hate is when you get those really *good* nights a few
> exposures is all you can manage before the sun comes up.  By the time
> I get the kids to sleep and then make sure I'm well aligned, it's
> midnight.  At least the nights are getting longer and the kids start
> going to sleep a little faster when it's already dark....
>
> roland
> --
>        PGP Key ID: 66 BC 3B CD
> Roland B. Roberts, PhD                             RL Enterprises
> roland@rlenter.com                     76-15 113th Street, Apt 3B
> roland@astrofoto.org                       Forest Hills, NY 11375
>
> --  APML Archives at <http://astro.umsystem.edu/apml/>  ---
>              Unsubscribe at <majordomo@seds.org>
>



--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>