Owl Nebula (M97)

Owl Nebula
All Images
Copyright Steve Cannistra

Please click here for a larger image (80%).

Size: About 4.7'
RA: 11h 15m 18s
Dec: 54 degrees 58' 16"
Position Angle:  plus 6 degrees (Pinpoint)

The Owl Nebula (M97) is a planetary nebula in Ursa Major, discovered by Pierre Mechain in February 16, 1781.  This is the first light image from my new telescope, a modified Cassegrain model Vixen VC200L (200 mm aperture, focal length 1800mm, f9).  I chose this scope because I wanted to image at longer focal lengths, but I also needed to minimize the weight of my equipment since my set up is entirely portable and non-permanent.  At a focal length of 1800mm, weighing in at around 13.2 lbs (6 kg), and yielding very flat fields, this scope was perfect for my needs. 
In addition, I considered the fact that the best seeing in my location is in the range of only 2.5".  With the Apogee U32 camera (KAF3200 chip with 6.8 um pixels), at a focal length of 1800mm, my image scale is 0.78"/pixel.  As predicted by Nyquist, this image scale is well matched for seeing in the range of 2.34" (0.78 x 3).  So although I could spring for a higher focal length set up, it would be heavy, would cost more, and I would not get any greater resolution since I am already seeing limited and well sampled at a focal length of 1800mm.  More information about the formation of the Owl Nebula may be found on the SEDS website as well as Rob Gendler's website.

Photographic Details:

Date:  March 8 and 9, 2008
Scope:  Vixen VC200L at f9 on the Takahashi NJP Mount.
Autoguider:  SBIG ST-402 with Sky90 at f4.5.
Camera:  Apogee U32 -20C.

Astronomik 6nm Ha filter and 13nm OIII filter.
Exposures:  Ha:  8 x 20'; OIII:  8 x 15'.  Note that at f9, neither of these subexposure durations was truly photon noise limited.  I need to go longer in the future.  Total exposure 4.7 hours.
Conditions:  Temperature was approximately 28 degrees F over the course of the night.
Post-processing:  This is an Ha:OIII:OIII composite taken in moonlight (i.e., no RGB).  Calibrated, aligned, and Sigma Clip combined in Maxim, followed by deconvolution using Bob Vanderbei's Fat Tail Deconvolution script.  DDP in ImagesPlus (IP).  Further processing in Photoshop CS (16 bit format).

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