RE: [APML] Stacking the right negatives

["Jeff Ball" <jeffball@zoominternet.net>]

Alan,
My preference is to go as deep as sky glow or polar misalignment will allow
you with an exposure and then stack exposures of the same duration. The
dimmer areas of the 3 hour exposure will not benefit from a stack with a one
hour exposure.  They will actually be minimized by your combination
techique, either average or sum.  To reveal the dimmer parts of the 3 hour
shot, you would have to reduce the amount that the one hour shot would
contribute to the combination.  That would reduce the benefit the image will
receive from 50/50 combination with regards to grain reduction.  If you
stack 2 x two hours, now you have a good compromise in deep exposures of
similar duration that will both contribute 50% of the total composite and
maximize your grain reduction.  I believe the only scenario where two
different exposures is beneficial is where you are trying to mask
overexposed areas of deep exposure.  I look forward to the response of
others and I am sure the archives has an extensive list of resources with
mathematical explanations.  Best wishes.
Jeff Ball

-----Original Message-----
From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]On
Behalf Of Alan Voetsch
Sent: Friday, December 06, 2002 7:24 PM
To: APML
Subject: [APML] Stacking the right negatives


Hi all,

Later tonight, or tomorrow I will be attempting my
first stack, yep still a virgin. :-)

I know with an obnject like M42 it's wise to have a
wide range of exposures in your negs, 2 minutes, 5
minutes, 45 minutes as an example. With the typical
DSO, say the HH, would this strategy be entirely
different? Would 2 two hour shots be preferable to a 1
hour and a 3 hour shot? These are just examples, but
you get my drift. Are we better off with 2 of about
the same exposure, or two that are somewhat different?
Why, or why not?

Thanks,
Alan



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