Exploring bi-colour palettes with an SV605MC, a William optics 81mm APO refractor and AstroDMx Capture

Bi-colour images of the Horsehead and Flame nebulae

The Horsehead and Flame nebulae were imaged with AstroDMx Capture, a William Optics Super Zenithstar 81mm ED Doublet APO refractor at f/5.5 with x 0.8 reducer/flattener, (F=445.5mm) and an SVBONY SV605MC monochrome, cooled CMOS camera fitted with a 7nm H-alpha, or a 6.5nm OIII filter or an Altair Quadband filter whose transmission curve extends to long enough wavelengths to include SII. 

As usual, the mount was placed on marks on the concrete base which give a fairly good polar alignment. AstroDMx Capture passed the time, altitude and location coordinates to the hand controller via the INDI server. The hand controller which now contained all of the correct information was set to its previous alignment and was unparked by AstroDMx Capture.

AstroDMx Capture was used to send the scope/mount to a bright star to check focus with a Bahtinov mask. 

Then AstroDMx Capture sent the scope/mount to the mag 7.5 star HD37805, which lies roughly central within the Horsehead-Flame nebulosity. This is a preferred way to compose the image, than sending the scope/mount to the published coordinates of the Horsehead or the Flame nebula.

AstroDMx Capture plate-solved the field of view and centred the selected HD37805 star

6 x 5min exposures were captured with each of the OIII and H-alpha filters, giving 1 hour total exposure time, plus 15 x 2min exposures through the Quadband filter, extending the total exposure time to 1 hour 30 minutes. All of the captured images at all wavelengths were stacked together to produce a luminance image.

AstroDMx Capture capturing H-alpha data

AstroDMx Capture capturing O3 data

The data were stacked and partly processed in Siril and post-processed in the Gimp 2.10 and Neat Image.

Three false-colour palette rendering of the results are shown here:

The first bi-colour image maps HOO to RGB and then the luminance is blended into the image

The second bi-colour image uses a synthetic green channel produced as the stretched product of the H and O images and then the luminance channel is blended into the image.

The third bi-colour image maps OHO to RGB and then the luminance is blended into the image.

There are, of course, a number of possible combinations of the two colour channels O and H:

The SV605MC camera performed flawlessly with AstroDMx Capture and will be supported by the imminent release of Version 2.