Imaging nebulae in Cepheus with AstroDMx Capture
The two nebulae imaged in this session were The Wizard nebula and the Elephant trunk nebula.
Equipment used
Exposures were captured with AstroDMx Capture through an Altair Starwave 60 ED refractor with an 0.8 reducer/flattener, an Altair Quadband filter and an SV605CC 14 bit OSC CMOS camera. The scope was mounted on a Celestron AVX mount.
The Altair Quadband OSC narrowband filter transmits two spectral bands:
FWHM spans 477.5nm - 512.5nm at the blue-green end of the visible spectrum and FWHM spans 642.5nm - 677.5nm at the red end of the spectrum.
The first band contains the emission lines of H-beta at 486.1nm and OIII at 495.9nm and 500.7nm and is centred on 495nm.
The second band contains the emission lines of H-alpha at 656.3nm and SII at 672.4nm and is centred on 660nm.
The Filter is, as we have seen, dualband; however it is called ‘Quadband’ because it contains the emission lines of these four elements.
Each of the two transmission bands has a fairly wide FWHM of 35nm and the rest of the visible spectrum is blocked. The filter’s two spectral bands are quite wide and it is an effective light pollution filter.
As usual, the mount was placed on marks on the ground which quickly gives quite a good polar alignment if care is taken with the placement of the tripod feet.
AstroDMx Capture running on the imaging computer indoors sent the scope/mount, via an INDI server running on the same computer, to the star Altair and the scope was focused on the star using a Bahtinov mask.
An SVBONY SV165 guide scope with a QHY-5II-M guide camera was used for PHD2 multistar pulse auto-guiding. The auto-guiding was controlled by a separate Linux laptop indoors.
NGC 7380, The Wizard nebula. NGC 7380 is an open cluster of stars in the constellation of Cepheus. It was discovered by Caroline Herschel in 1787. The surrounding emission nebulosity is known as the Wizard Nebula.
AstroDMx Capture sent the scope/mount to NGC 7380 with plate solving and was used to capture 1 hour’s worth of 5 minute exposures of the Wizard nebula. During the imaging session, Dark frames, Flat fields, Dark Flats and Bias calibration frame were captured.
Capturing Flat fields at the end of the session using a variable illuminated tracing panel as a uniform light source.
Screenshot of AstroDMx Capture acquiring 5 minute exposures of the Wizard nebula
With a negative preview
The data were calibrated and stacked in Deep Sky Stacker. An important function in DSS that it is important to use when setting up the stacking parameters, is the function to remove hot and cold pixels and replace them with the median of the surrounding pixels.
This is an objective and very effective way of removing these artefacts and saves very laborious and subjective work with a healing brush during post processing.
The resulting stacked image was processed in GraXpert, Gimp 2.10, Neat Image and Photoscape X Pro.
Initial stretching and background extraction in GraXpert
Final image of the Wizard Nebula
IC 1396 The Elephant trunk nebula
AstroDMx Capture sent the scope/mount to IC 1396 with plate solving and was used to capture 50 minutes’ worth of 5 minute exposures of the Elephant trunk nebula until clouds came in.
Screenshot of AstroDMx Capture acquiring 5 minute exposures of the Elephant trunk nebula
With a negative preview
The data were calibrated and stacked in Deep Sky Stacker and the resulting stacked image was processed in GraXpert, Gimp 2.10, Neat Image and Photoscape X Pro.
Initial stretching in GraXpert
No stretch
Stretched
Final image of the Elephant trunk nebula
The SV605CC camera performed well with AstroDMx Capture and the Altair Starwave 60 ED refractor with an 0.8 reducer/flattener.
During stacking the hot and cold pixel removal in Deep Sky Stacker was particularly useful and the use of GraXpert to do an initial stretch, with or without background extraction proved to be very effective.
Nicola is currently working on implementing INDIGO in AstroDMx Capture. This is a lengthy process for which many weeks of code refactoring preparation have already been done. We will announce here when INDIGO becomes available in AstroDMx Capture.
