Re: [APML] Magnitude limit and exposure

["Don Westergren" <westergren@netzero.net>]

Nicola,

Try using E200 or Provia400 on M17, M8 and M20.  Since M20 has some rich
blue, the Provia would be the better choice for it.  The Swan or Omega
Nebula M17 has some very bright elements and some dimmer parts.  If you
shoot it at 5, 10, and 20 minutes, you will see quite different results.
You will find that there is no perfect exposure for a particular "magnitude"
object.  Generally shoot as long as you can without getting sky fog to get
the most nebula or galaxy.  The exceptions are objects with extreme
brightness where you need to combine short and long exposures to see both
the bright and dim elements.  Examples are M17, M8 (very short exposure for
the Hour Glass, long for the Lagoon), Orion Nebula M42, and Andromeda Galaxy
M31.

I shoot a lot at f/9 with autoguider up to 3 hours without getting sky fog
with Provia400.  I started out manual guiding with 15 minutes shots and
gradually worked up to 90 minutes.  Your challenge is to learn to guide and
get comfortable with longer exposures that allow a lot more targets.  One of
the secrets of good and easy manual guiding is to start with good polar
alignment.  Assuming your mount has reasonable small periodic error, good
polar alignment almost eliminates Dec corrections so you can concentrate on
one axis.

Good Luck,
Don


Dear All,

I'd like to try for the very first time to shoot prime focus.
Because I'm manual guiding I guess I'll try with a very fast film (any
suggestion)
and a short exposure (not more than 20 minutes). Is there a way to calculate
which magnitude I can reach depending on the scope f/ratio, film,
reciprocity
ratio and time? I already know I won't reach the sky fog limit, but I'd
like to give a try to see if I can manage at least focusing and guiding
to obtain a reasonable result on some object (any suggestion on a bright
target?)
My scope is a Vixen SP 102M (acromatic) f/10

regards,
Nicola
http://astrofoto.laza.it

_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo




_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo