Sunday, August 1, 2010

Stacking no Tracking

It might seem strange but honestly I never considered that there would a condition somewhere in between Raining Like Cats and Dogs and Darkest Skies You Have Ever Seen.  Not only is there such a condition it is by far the most likely one I am going to experience if there is any break in the seeming perpetual cloud-out.

Actually it happened last night.  It was raining at 9pm.  By chance happened to look up at 9:40pm and ... "that's a funny cloud".  Yeah.  It's commonly known as the Milky Way.  Now mind it is still partly cloudy but I was still elated to see a "poke your eye" out MW.   It takes me 20minutes to get back to our hovel and decide that it is not worth it to pull out the Astrotrac and go full-auto.  Instead I just grab the tripod, a 50mm f/1.4 lens and figure I take some short duration shots under various conditions so I can say that I at least took some kind of image of the stars.  Basically I was going out with not one piece of equipment that I so painstakingly shipped out to New Mexico.  No mind ... I'm on it.

About 45min later the sky was extinguished and the rest of the night was full of lightning and heavy rain. None-the-less I got a couple images and learned some lessons.  Lessons first - images later.

1.) The 50mm f/1.4 lens is cool (so much freaking light) but it is no red-stripe.
2.)  It is near impossible to focus at f/1.4 while looking at a live view screen.
3.)  Plop down some $$ for a nice carbon fiber tripod.  Cheapie tripods, well, lets just say some language that I wouldn't use around the girls was spoken into the night air.
4.) In a serious pinch ISO3200 will do.  A serious pinch.  Noisy but OK if you downscale.
5.) Don't panic and shoot wide open.  The lens can buy you a lot even stopped down a notch or two.
6.) Acceptable trailing is in the eye of the beholder.  My eye didn't like anything more than 10sec with a 50mm lens.
 7.) Trying to frame a shot near the zenith while mounted on a tripod is desperation in action.

Never shy to try something completely new and abandoning my detailed planning (read making stuff up on the spot) I thought I might shoot a bunch of short duration frames, shoot some darks, and try to stack 'em.  While my images look like crayola (bad focus, jumpy tripod, lens not set correctly) I think this idea has merit (I'm sure others have tried this).

So ideally one would:
1) shoot as high an iso as acceptable
2) lens as wide open as acceptable (but probably stopped down a bit)
3) turn off in camera dark frame
4) shoot a bunch of darks to bang down the noise
5) shoot flats (I didn't and wished I had)
6) stack lights with translation and rotation settings and let software take care of image shift
7) process to your hearts content

With some practice and experimentation I think some very nice wide field images could be had with no tracking mount at all.  The below is a stack of 25 10sec exposures at f/1.4 and ISO3200.  Same number of darks.  All on a static tripod - no tracking!

Cygnus near Deneb with a tiny teeny North American nebula below.  Wish I had come at least somewhere near focus and shot some flats.

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