The Cave nebula (Caldwell 9) in Cepheus was imaged with AstroDMx Capture, a William Optics Super Zenithstar 81mm ED Doublet APO refractor at f/5.5 with x 0.8 reducer/flattener, and an Altair 2" magnetic filter holder v2 fitted with a 7nm H-alpha, or a 6.5nm OIII filter or a 7nm SII filter. An SVBONY SV605MC monochrome, cooled CMOS camera was placed at the focus. The scope was mounted on a Celestron AVX mount which was controlled by AstroDMx Capture via an INDIGO server. The scope is fitted with a ZWO AEF that is also controlled by AstroDMx Capture via the INDIGO server that runs on the imaging computer.
The equipment used
The two scopes were fitted with heating anti-dew strips as was the ZWO AEF which on a previous occasion proved to fail in cold conditions.
An SVBONY SV165 guide scope with a QHY-5II-M guide camera was used for PHD2 multistar pulse auto-guiding via the same INDIGO server. The auto-guiding was controlled by a separate Linux laptop indoors.
The scope was focused on a bright star using a Bahtinov mask.
Six 5-minute exposures of the Cave nebula were made through each of the H-alpha, SII and OIII filters, giving a total exposure time of an hour and a half. Matching dark frames were captured along with Flats which were captured through an Altair Quadband filter, and Bias frames were also captured.
The subs were calibrated and stacked in Siril. The resulting three stacked channel images were balanced in the Gimp. The three channel images were aligned, combined as an SHO palette, stars removed and the starless image denoised in PixInsight. The image was then post processed in the Gimp, Siril, PS CS2 and the stars were added back in the Gimp.
SHO image of the Cave nebula C9
