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Contains:  NGC 7023
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The Iris Nebula (NGC 7023)

Technical card

Dates:June 11, 2018July 8, 2018July 10, 2018July 31, 2019Aug. 1, 2019

Astrodon Tru-Balance Gen2 E-Series - B 36mm: 85x45" (gain: 54.00) -20C bin 1x1
Astrodon Tru-Balance Gen2 E-Series - B 36mm: 57x90" (gain: 54.00) -20C bin 1x1
Astrodon Tru-Balance Gen2 E-Series - G 36mm: 120x45" (gain: 54.00) -20C bin 1x1
Astrodon Tru-Balance Gen2 E-Series - G 36mm: 58x90" (gain: 54.00) -20C bin 1x1
Astrodon Tru-Balance Gen2 E-Series - L 36mm: 240x120" -20C bin 1x1
Astrodon Tru-Balance Gen2 E-Series - R 36mm: 45x180" (gain: 54.00) -20C bin 1x1
Astrodon Tru-Balance Gen2 E-Series - R 36mm: 80x45" (gain: 54.00) -20C bin 1x1

Integration: 16.7 hours

Darks: ~50

Flats: ~20

Bias: ~100

Avg. Moon age: 21.40 days

Avg. Moon phase: 9.21%

Bortle Dark-Sky Scale: 5.00 job: 2847861

RA center: 21h 1' 20"

DEC center: +68° 2' 42"

Pixel scale: 0.974 arcsec/pixel

Orientation: 276.314 degrees

Field radius: 0.534 degrees

Resolution: 3151x2384

Locations: Home Observatory, Schenectady, New York, United States

Data source: Backyard


The Iris Nebula (NGC 7023, Caldwell 4, LBN 487) is a bright reflection nebula in the constellation Cepheus. The nebula (LBN 487) is lit by a magnitude 7 star (SAO 19158). It is located 1,300 light years away and it is 6 light years across.

This image is the result of a combination of data collected over two years. Last year, I collected color data with the Tak FSQ106 refractor, but only collected a limited amount of luminance data. I wanted to attempt to achieve sufficient SNR in the dust surrounding the nebula, which is challenging in my home Bortle 5 skies. I opted to use the TS ONTC 10in Newt to collect luminance data. The much higher efficiency and etendue of the large mirror combined with bigger pixels (KAF8300) boosted SNR collection per unit time compared to the 10cm refractor with tiny pixels, at roughly the same image scale.

To emphasize the nebula I chose to apply slight star de-emphasis using Adam Block's technique. It is a wonderful method to reduce star presence in an image, which results in more natural presentation than morphological transformation. In panels D and E, you can see the effect of star de-emphasis right after LRGB combination.

Color data (2018): Tak FSQ106 with ZWO ASI183MM Pro (Gain: 54, Offset:10)
Luminance data (2019): TS ONTC 10in f4 with Atik 383L+



Luca Marinelli
License: None (All rights reserved)



Description: Orginal stars without shrinking.


Description: Before star de-emphasis.


Description: After star de-emphasis.


Description: Complete reprocess of the data, including Adam Block's star de-emphasis technique.


Description: Local contrast and curves transformations to enhance the dust.


Description: Slight reduction in median level of the nebulosity and contrast in the dust.

Sky plot

Sky plot


The Iris Nebula (NGC 7023), 


            Luca Marinelli