The Ghost Nebula is situated in the constellation Cepheus and consists of Dark Nebula and Reflection Nebula. There are several stars embedded giving the Nebula its yellowish glow. Dark Nebula consists of gas so dense that light does not shine through.
For this image I used the EdgeHD 8″ telescope with the 0.7 reducer together with ZWO 2600 MM pro camera. I took 17 images of 5 min duration with each R, G and B filters and 67 images with the Luminance filter. In total 10 hours of exposure for this Nebula.
In order to reduce the noise in the image, calibration frames are usually taken. These are Flat frames, Bias frames and Dark frames. Flat frames are obtained with a soft and even light from a light source in front of the telescope to reveal dust motes on the lenses and filters, and vignetting caused by the image train. The light source I use for this is a light table normally used for drawing. Bias frames are taken under dark conditions with very short exposure to remove the bias which is a charge applied to the sensor to prepare it to receive photons. Finally, Dark frames are exposures taken under dark conditions at the same temperature and exposure time as the Light frames (i.e. images of the object). Dark frames reveal and remove dead pixels and noise in the camera sensor that inevitably comes from long exposures despite sensor-cooling.
The signal to noise ratio is then further improved by the stacking procedure in PixInsight, i.e. the program I use to process these images.
The resulting “master-image” is then further processed in PixInsight to sharpen details/stars, reduce noise even more and to enhance contrast and color. All of these processes are necessary since the light captured from the Nebulae is quite dim, and light-pollution is usually significant.