Re: [APML] NGC 7023 aka Iris Nebula

Tony,

A fine image! I really don't understand the explanation for the increased S/N.

Exposure time is exposure time. As long as the subexposures are sufficient

to exceed the readout noise its all the same S/N whether you stacked shorter

subexposures or did one long exposure. I'm a bit confused.

Rob Gendler
Email: robgendler@att.net
Web site: http://www.robgendlerastropics.com/

----- Original Message -----

From: Tony Hallas

To: Discussion of Film Astrophotography

Sent: Thursday, October 23, 2003 7:06 PM

Subject: Re: [APML] NGC 7023 aka Iris Nebula

Hello,

     I recently completed an image of what has to be one of the most beautiful objects in the sky, NGC 7023, or what I call the Iris Nebula. I took this image from my home observatory with average seeing and not very clear skies ... still need that first rain storm to wash out the air ... the Milky Way looked rather dim when I took these. But the CCD seems to cut through the muck like magic ...

     Data for this is a bit different ... I shot with equal exposure lengths for the RGB (so you only need one dark frame), but I shot 1.7X the number of blue exposures. When the RGB data was assembled, there was more S/N for the blue, so when it was stretched to achieve the correct color balance, all three colors had approximately the same S/N.

    The rest was pretty standard fair ... MaxIm to reduce and align, Sigma to blend, PS to extract and process the image.

    Guess after wading through all this you might want to see it... please go to:

    http://www.astrophoto.com/NGC7023.htm

    All comments are welcome ...

        Tony

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