SaratogaSkies Jim Solomon's Astropics

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December: Test shots with new scopes/mounts

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NGC 884 & NGC 869 (Double Cluster)

Mouse-over to see annotations. (Requires Javascript) Click to see high-res version.

Image Details:

Camera: Mofidied Canon Rebel XT (350D): Hutech Type I Filter Replacement
Mount: Celestron AS-GT
Scope: Orion ED80 (80mm f/7.5 APO Refractor)
Configuration: Focal Reduced
Additional Optics: TeleVue #TRF-2008, 0.8x Reducer/Flatener For TV-85 And TV-76
Filter: None
Effective Focal Length: 480mm
Effective Focal Ratio: f/6
Exposure: 13 x 4min @ ISO 400
Total Exposure: 0hrs, 52min
Date: 11/12/2005 11:06:31 PM PST (start)
Location: Saratoga, CA, USA
Acquisition: DSLRfocus
Focus: DSLRFocus
Dithering: GADFly 1.0.5
Guiding: GuideDog via Philips ToUcam Pro II (840k) through Orion ST80 w/ Celestron 2x "Kit" Barlow

Processing:

  • IRIS: Dark subtraction, registration, gradient removal
  • JimP: Flat field, Kappa-Sigma Stacking, White balance, ASINH stretching
  • Photoshop: Levels, cropping, JPG conversion

Image Description:

This is NGC 884/869, aka, the Double Cluster in Perseus. This shot was a test of the suitability of the TeleVue 0.8x Focal Reducer/Flatener for use with the Orion ED80 refractor. (Big thanks to Jim Nomura for letting me borrow the TeleVue!) This test was prompted by my disatisfaction with the combination of the ED80 and the Celestron 0.63x reducer which, of course, was never designed to be used with a refractor. (An example of the Celestron can be seen in my latest M31 shot.)

I've added this current shot, and the M31 shot, to my ED80 Reducer Shootout page. Based on this data, the Willam Optics Focal Reducer appears to be the best fit for the ED80. Time to trade in the Celestron. <grin>

Anyway, this shot turned out ok, despite a 91% full moon. And I have very few images of Open Clusters, so I decided to post this one. A higher-resolution image is also available. North is up.

 
NGC 6992 (Network Nebula)
SaratogaSkies Jim Solomon's Astropics

Search

Latest news

December: Test shots with new scopes/mounts

Dec 21: TMB 80/480 Arrives!

Dec 3: AP1200 Arrives!

Nov 30: TMB 152/1200 Arrives!

Links:

NGC 6992 (Network Nebula)   [obsolete]

Click to see high-res version.

Image Details:

Camera: Canon Digital Rebel (300D)
Mount: Celestron AS-GT
Scope: Celestron C8-N (8" f/5 Newtonian)
Configuration: Prime Focus
Additional Optics: Celestron/Baader Multi Purpose Coma Corrector (MPCC)
Filter: None
Effective Focal Length: 1000mm
Effective Focal Ratio: f/5
Exposure: 14 x 8min @ ISO 400
Total Exposure: 1hrs, 52min
Date: 8/25/2004, ~1:30am PDT
Location: Saratoga, CA, USA
Acquisition: DSLRfocus
Focus: DSLRFocus
Dithering: None
Guiding: GuideDog via Philips ToUcam Pro II (840k) through Orion ST80 w/ Celestron 2x "Kit" Barlow

Processing:

  • IRIS: Dark subtraction, flat field, registration, Kappa-Sigma stacking
  • Photoshop: Levels, image size, JPG conversion

Image Description:

This is NGC 6992, the Network Nebula, the Eastern portion of the Veil Nebula in the constellation of Cygnus. The Network/Veil is the remnant of a supernova explosion. The entire object takes up nearly 4 degrees of sky. For comparison purposes, the full moon takes up only 1/2 a degree. Better framing would have captured more of this object, but to capture the entire object requires a shorter focal length (such as that provided by the ST80 ... hmmmm) or a mosaic of several shots. Since my main mission was to test out my new focuser, the new coma corrector, and to experiment more with GuideDog, I wasn't so much worried about the framing of the object. I regret this decision, because the shot turned out to be one of my best to date.

Anyway, a coma corrector attempts to minimize or eliminate "coma", the primary form of aberration of paraboloid optics, such as those in a Newtonian reflector. Without such a device, the stars and other details in the outer portion of an image tend to "blur outward", not unlike the tail of a comet, which is how the term "coma" came into being. ("Like I'm in coma" is pretty much how I feel the day after going to sleep at 4am after a night of astrophotography, but I digress.) Anyway, the MPCC seems to have done a good job correcting the coma in the image, as stars are much more "pinpoint" from edge-to-edge of the frame.

But to reach focus with the camera and the MPCC in place, I needed to upgrade my focuser to a "low profile" one. The JMI NGF-DX3 seemed to be a good choice, and I'm pretty happy with it so far. Also, I tried cranking the "aggressiveness" setting in GuideDog which resulted in better tracking than previous attempts. Finally, I chose ISO 400 instead of ISO 100 based on the results of a noise analysis I performed on the Digital Rebel. ISO 400 looks to be a good choice, but more experimentation is needed.

This is a (very) slight crop of the full frame, scaled for display on the web. North is up.