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Contains:  NGC 6871, The star 27Cyg
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Sh2-101 - Tulip Nebula, 


            Walter Koprolin
Sh2-101 - Tulip Nebula
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Technical card

Dates:Sept. 8, 2012

Frames: 71x600"

Integration: 11.8 hours

Avg. Moon age: 22.11 days

Avg. Moon phase: 50.43%

Basic astrometry details job: 3054895

RA center: 20h 3' 46"

DEC center: +35° 19' 4"

Pixel scale: 4.984 arcsec/pixel

Orientation: 358.768 degrees

Field radius: 1.387 degrees

Resolution: 1600x1207

Locations: Ebenwaldhöhe, Kleinzell, Lower Austria, Austria

Data source: Traveller


I acquired the narrow-band data during 5 different nights at 3 different locations. I got 7.3 hours of usable Hα data, but only 4.5 hours of [OIII], and only 20 minutes of [SII] because of incoming clouds. So I decided to skip the [SII] data altogether. [OIII] data was very noisy, but usable for creating a tone map. The Hα data was not uniform because of different sky conditions and different framing in individual nights, the left part of the image actually got 2 hours more of dark-sky Hα exposure than the right part.

Processing steps: Basic data reduction, registration and combination, background flattening, noise reduction, deconvolution, non-linearization, star-background separation, local contrast enhancement, star size reduction, color synthesis using tone mapping, color correction, re-adding of the stars.

Tonemap composition:

Red = Hα
Green = [OIII]
Blue = [OIII] + 15% Hα to compensate for missing Hβ

Master Luminance composition:

L = Hα + 24% [OIII]

Some color-tweaking was required after tone mapping because the result was way too greenish.

Sidenote on colors: Tone mapping exaggerates the green-blueish [OIII] contribution. Red Hα has about 10x more intensity in the Tulip Nebula than [OIII], as I measured it. So, in "camera reality", the nebula should look totally red. But then again, the human eye is not very sensitive to Hα, but much more so to [OIII] and Hβ. So maybe the color scheme is not that far off from what the human eye would see if the nebula was bright enough.



Walter Koprolin
License: None (All rights reserved)

Sky plot

Sky plot


Sh2-101 - Tulip Nebula, 


            Walter Koprolin