Michael,
For deep sky nebulous objects I always take multiple 5 minute exposures
regardless of the object. Some people take 10 minute exposures. You need
lots of total exposure for these objects regardless of their stated magnitude.
Multiple exposures reduce effects of random noise, which is reduced by the
square root of N. Thus, stacking 4 exposures reduces noise by a factor of 2.
Sixteen exposures reduces noise by 4. Don't worry too much about the stated
magnitude. It's the "integrated magnitude" and doesn't correspond to the
surface brightness, which is more important in photographs. In the case of
bright star clusters without nebulae, like M13 or M3 or the Double Cluster, you
may want to try shorter exposures to prevent bad saturation of the brighter
stars.
Paul Lind
----- Original Message -----
From: Michael McDonald <mikemac@xxxxxxxxxxx>
To: az-observing@xxxxxxxxxxxxx
Sent: Tue, 02 Oct 2018 23:56:02 -0400 (EDT)
Subject: [AZ-Observing] Exposure estimate?
As some of you may have figured out, I’m new to all of this astronomy stuff. I
just about have everything ready for this weekend’s AASP and I’ve started
dreaming about what objects I’m going to try to image. But in order to make a
sensible target list, I need to make a reasonable estimate of how much exposure
time I should give each target. And I have no idea or feel for where to even
guess! I’m hoping one of the more experienced imagers could give me a hint as
to where I should start.
Everything currently on my tentative list is between 6 and 8 magnitude
(according to Stellarium). My scope is f10 plus a f6.3 reducer. I have a mono
ZWO camera so everything will be LRGB or maybe some Ha thrown in if I get brave.
Suggestions? Hints?
Michael McDonald
mikemac@xxxxxxxxxxx
Trifid Nebula
Crescent Nebula
Helix Nebula
Triangulum Galaxy
Orion or Horsehead Nebula if I’m up that late--
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