Astronomy
I'm thinking that this slow-motion blog of astronomical photos
and
misadventures should begin with a reasonably successful outing.
Additional pages may provide ample space to vent about the
sisyphusian
enterprise that astrophotography often is.
November 23-24, 2006
The telescope is in the side yard, south of the house, where mid-northern objects rise through the gap in the pines that is the 19th fairway, aka, the back yard.
Today's project: get the webcam and the Shoestring adapter to work with Maxim DL/CCD so I can make subexposures longer than 2 minutes. The longer I can make the subs, the less time I have to spend combining them into long exposures of the deep sky. Tonight, I want to make a series of 10-minute subexposures to be sure that the guiding scheme works before trying to refine it into a suite of hard- and software that can guide the DSLR or the dedicated astro CCD, either behind the main telescope or behind a fast telephoto, a setup I don't have to figure out everytime I go out for pictures, something that can be assembled and taken down in a few minutes, either here or at a remote site... You know: everything.
Tonight's outfit: a Losmandy G11 mount carrying an Astro-Physics 5-inch F6 refractor (telecompressed to F4.5) with an Orion Short-Tube 80 mounted in 3-point rings up top as a guide telescope. A Canon 20D DSLR sits at prime-focus of the A-P refractor, and a Philips VestaCam (an unmodified webcam) is mounted at prime focus of the ST80 for guiding duties. All this is controlled by Maxim DL/CCD running under Windows XP on a Sony Vaio SRX87 notebook computer. A DLink powered USB hub lets me connect the VestaCam and a Shoestring Astronomy GPUSB guiding adapter to the Sony. So it works like this: the webcam is streaming images of a guidestar to the computer where Maxim checks on it every ten seconds; if the star has moved, Maxim sends signals out through the Shoestring guideport to tell the G11 mount how to move the telescope to put the star back where it was. Meanwhile, behind the main telescope, the Canon 20D is running a series of ten minute exposures which it is storing on its internal CF card (enough cables already, let it store the shots internally for now). The Canon could be controlled through the computer, too, with still more cables, but for now I'm using its timer/remote release to program the exposures: n frames, x seconds long, seperated by y seconds (to let vibrations settle). In addition to Maxim, the notebook computer is running Access RemotePC server so I can sit in my office about fifty feet away and drink coffee, read email, tweak web pages, whatever, while watching the notebook computer's screen and making adjustments via WiFi in a window on my desktop. All in all, it's a pretty cushy setup.
OK, so it was a clear night in November. Seeing was awful but transparency was decent. I was seeing mostly 0.5-1 pixel corrections in all four directions. Considering the guide-scope's focal length and the pixel size of the guider, that's 1.5-3 arcsecond corrections every ten seconds. Clearly, the guider was chasing seeing. Next time, I'll try less aggressive guide settings (and hope for steadier air).
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Text & Photos by David
Cortner
Link all you like; please
get in touch for other uses.
Messier 31 – the Andromeda Galaxy, with companions
50 minutes, 5-inch F6 A-P refractor at F4.5,
Canon 20D, iso 800, raw format,
5, 600s exposures. Averaged in Maxim,
dynamic masked in Photoshop CS2,
partially histogram equalized in CS2.
Messier 45 – The Pleiades
90 minutes, 5-inch F6 A-P refractor at F4.5,
Canon 20D, iso 800, raw format,
9, 600s exposures sigma combined in Maxim using
two-star auto-correlation to minimize field rotation (where'd that come
from?),
cropped and curves-adjusted in Photoshop CS2.
I mixed a single sharpened frame back into the
porridge to retain a feeling of brilliance in the stars.
Is all that glowing stuff to the left real? We'll see.
Cable management after tear-down in
the
dark.
Work on this.