Cave Nebula, Sh2-155

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This nebula in Cepheus is very faint and I've found to be a hard subject for my DSLR, even if I had gathered a long exposure under a dark sky. Heavy noise is unfortunately present, expecially in the blue channel. The main red part of the nebula is catalogued as a Sharpless object, Sh2-155, or LBN 527. The blue part below is VdB-155. A couple of the small nebulas on the lower-center border are GN and GN 22.55.2. Many dark nebulas are present, the main ones are LDN 1218 (at left of Cave) and LDN 1215 (at right).

Technical Data
Optics TEC 140
Focal Length
1011 mm
Focal Ratio f/7.2
Exposure Time 4h20m (single exp of 10 min)
CCD Canon EOS 5D with Baader filter
Sensitivity 800 ISO
Location Colle dell'Agnello (CN, Italian Alps) at 2700 m height
18 August 2012
Mount Gemini G-41
Tracking Lodestar on an 80mm f/5 refractor
Temperature and humidity T= +14°C, RH=40-60%
Sky brightness at zenith (with SQM-L) 21.4-21.5 mag/arcsec^2
Notes Very faint object. Heavy noise due to the faintness and maybe also to the high temperature (very hot month even at high altitude).

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