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December: Test shots with new scopes/mounts
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M1 (Crab Nebula)
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| Click to see high-res version. |
Image Details:
- Camera: Mofidied Canon Digital Rebel (300D): Hutech (no filter)
- Mount: Celestron AS-GT
- Scope: Celestron C8-N (8" f/5 Newtonian)
- Configuration: Negative Projection (Barlowed)
- Additional Optics: TeleVue 2x Barlow
- Filter: None
- Effective Focal Length: 2250mm
- Effective Focal Ratio: f/11.1
- Exposure: 39 x 8min @ ISO 800 (total over 2 nights)
- Total Exposure: 5hrs, 12min
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- Date: : 3/2/2005 7:57:06 PM PST (start) and 3/5/2005 7:39:22 PM PST (start)
- Location: Saratoga, CA, USA
- Acquisition: DSLRfocus
- Focus: DSLRFocus
- Dithering: Manual
- Guiding: GuideDog via Philips ToUcam Pro II (840k) through Orion ST80 w/ Celestron 2x "Kit" Barlow
Processing:
- IRIS: Dark subtraction, flat field, registration, cropping, Kappa-Sigma stacking
- JimP: White balance, ASINH stretching
- Photoshop: Levels, image scale, JPG conversion
Image Description:
This is M1, a Supernova Remnant in the constellation of Taurus. This was a rather ambitious project to shoot a relatively small object at a high focal length (and, unfortunately, a correspondingly slow f/ratio). This is two nights worth of imaging, a total of 5.2 hours of exposure. But due to the "square law" of focal ratios, this is equivalent to only 1 hour at f/4.9, which is the focal ratio of most of the shots I've taken.
The first night's frames (19 of the 39) were taken with my Unmodified 300D. The second night's frames (20 of the 39) were taken with fellow Saratogan Rich S.'s Modified 300D. No filters in either case, just the TeleVue 2x Barlow. The first night had better seeing, the second night had much better transparency.
Given the tracking ability of my mount (well over 1 arc-second of guiding error, RMS, in both axes), and the blurring effect of lousy seeing, I wonder if shooting at this higher focal length really increased the resolution over shooting at f/4.9. It certainly accomplished a quintupling of the required exposure time, but to what avail is the question -- and I'm too sick of shooting this object to try it again at f/4.9 for comparison. It'll have to wait til next year.
The image above is a 50% shrink of the full-size image, then cropped to 768x512 for display on the web. North is up.