SaratogaSkies Jim Solomon's Astropics


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C/2004 Q2 [Machholz] (Comet)

Image Details:

Camera: Canon Digital Rebel (300D)
Mount: Celestron AS-GT
Scope: Orion ED80 (80mm f/7.5 APO Refractor)
Configuration: Focal Reduced
Additional Optics: Celestron F/6.3 Reducer/Corrector (0.63x)
Filter: None
Effective Focal Length: 420mm
Effective Focal Ratio: f/5.2
Exposure: 65 x 2min @ ISO 800
Total Exposure: 2hrs, 10min
Date: 2/1/2005 7:24:34 PM (start)
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


  • IRIS: Dark subtraction, flat field, registration, cropping
  • JimP: N through M stacking, sequence ASINH stretching
  • Photoshop: Compositing, levels, image scale, JPG conversion
  • Premiere: AVI creation from individual frames

Image Description:

This is my second attempt at Comet C/2004 Q2 (Machholz), named after the San Jose Astronomical Association (SJAA) member Don Machholz who discovered it. See the ST80 image for a description of the processing steps and for a comparison picture. Perhaps the best-resolved object in this picture is Trumpler 3, the small Open Cluster of stars in the lower left (above the copyright notice).

To process this image, I used the technique described in this thread in the CloudyNights Forum. The difference is that I did all the machinations after ASINH stretching each individual frame, whereas I believe the author worked on the linear frames and only stretched the final result.

I had some major problems with the capture of this image:

  1. The ED80 was severely out of collimation when this was shot.
  2. The ED80 with Celestron f/6.3 Reducer has some field flatness issues, causing aberrations beyond the center of the frame. The collimation problem mentioned above exacerbates this.
  3. The framing of the comet, while asthetic in that there's "room" for both the ion and debris tails, places most of the interesting detail outside the "sweet spot" of the ED80 + focal reducer, making the signal to noise of the ion tail (in particular) quite low.
  4. There was tons of light pollution to the NorthWest, the direction this was shot on that night.
  5. My polar alignment was less than marvelous, causing roughly 0.5? of field rotation over the course of the imaging session. While IRIS is quite capable of derotating the frames, part of me believes that this function causes a loss of detail and an overall decrease in signal to noise.
  6. The comet was actually moving twice as fast (in arc-seconds per minute) than predicted by The Sky software. Had I known this, I might have gone for even shorter integrations (1min) at higher ISO (1600), since that would have been less than a pixel's worth of movement over the course of each frame, theoretically resulting in less blurring of each individual frame since I was guiding on a star, not the comet.
  7. The transparency that night was pretty awful.

So, that's my sob story, and all of the above show in the (lack of) detail in this image. Sniff. The movie (1MB AVI) is pretty cool and worth checking out. North is up.