SaratogaSkies Jim Solomon's Astropics


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NGC 6826 (Blinking Planetary)

Image Details:

Camera: Canon Digital Rebel (300D)
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: 2844mm
Effective Focal Ratio: f/14.2
Exposure: 51 x 30sec @ ISO 800
Total Exposure: 0hrs, 25min
Date: 7/15/2004, ~2am PDT
Location: Saratoga, CA, USA
Acquisition: DSLRfocus
Focus: DSLRFocus
Dithering: None
Guiding: None


  • IRIS: Dark subtraction, flat field, registration, Kappa-Sigma stacking, Wavelet processing
  • Photoshop: Compositing, cropping, JPG conversion

Image Description:

NGC 6826, the Blinking Planetary, is a planetary nebula in the constellation of Cygnus. It is so named because when you stare directly at the central star through the eyepiece of a telescope, the surrounding nebulosity all but vanishes. But when you avert your vision (i.e., look slightly off too one side), the nebula blinks into view. Why does this happen? Well, the human eye "sees better" off of center; i.e., you can see dimmer things not when looking directly at them, but by looking (slightly) away from them. So, when you're looking straight at the central star, the eye has trouble seeing the faint nebula that surrounds it. But when you look slightly away, your peripheral vision is sensitive enough to detect the nebula. It's very cool to try this in a decent telescope. It's a pretty amazing effect.

I used IRIS's Wavelet Processing capabilities to bring out details in the nebula. However, that made the surrounding stars and the sky background look icky, a technical term. So I used Photoshop to composite the wavelet-processed nebula with a non-wavelet-processed background using layer masks. There, I feel much better for coming clean. Also, I was very careful at every step of the aquisition and processing chain not to clip any of the nebula or its central star, in order to preserve the color and appearance of the nebula. This is a crop of the full-size image. North is up.