The Altair Dualband filters were explored with AstroDMx Capture through an Altair Starwave 60 ED refractor with an 0.8 reducer/flattener and 2" magnetic filter holder using an SV605CC cooled, 14 bit OSC CMOS camera. The scope was mounted on an AVX GOTO mount which was controlled by AstroDMx Capture via an INDI server running on the imaging computer indoors.
The Filters
Altair 6nm DualBand OIII SII ULTRA Filter Specifications:
1st band, OIII CWL 500.7nm FWHM 6nm ~0.5nm tolerance , T% 93% 0.5% Tolerance.
2nd band, SII CWL 671.6nm FWHM 5.5nm ~0.5nm tolerance, T% 93% 0.5% Tolerance.
Altair 6nm DualBand Oiii Ha ULTRA Filter Specifications:
1st band, OIII CWL 500.7nm FWHM 6nm ~0.5nm tolerance , T% 93% 0.5% Tolerance.
2nd band, Ha CWL 565.28nm FWHM 5.5nm ~0.5nm tolerance, T% 93% 0.5% Tolerance.
The equipment used
AstroDMx Capture sent the scope/mount to Vega and the scope was focused on the star using a Bahtinov mask using the Pegasus FocusCube v2 controlled by AstroDMx Capture via INDI.
An SVBONY SV165 guide scope with a natively connected QHY-5II-M guide camera was used for PHD2 multistar pulse auto-guiding via the INDI server. The auto-guiding was controlled by a separate Linux laptop indoors.
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.
Over two evenings, the same protocol was used to image a selection of nebulae:
40 minutes worth of 5 minute exposures were captured of each nebula through each of the two Dualband filters (with the exception of the Rosette nebula of which 45 minutes of 5 minute exposures were captured through each Dualband filter). Calibration frames were captured and flats were captured through an Altair Quadband filter using an illuminated tracing screen.
Capturing flats
The processing workflow
The data were calibrated, stacked and co-registered for both filters in Deep Sky Stacker using a common reference frame.
For each of the filters the component channels were separated into R, G and B monochrome images in the Gimp 2.10. The bandpasses of the two filters means that there is complete separation of the Ha and SII between the filters. The OIII is recorded in both the G and B channels. For each filter separately, I combined the G and B channels using the addition mode in the Gimp. This produced two separate B channels, one from each filter. I then combined the two B channels using the addition mode to produce a single B channel containing all of the signal from OIII captured through both filters. At this stage there were three 32 bit monochrome images: SII, Ha and OIII.
The three monochrome images were combined as an SHO image by ChannelCombination in PixInsight and full colour calibration using Hartmut Bornemann's AutoColor script and then the DeLinear script before saving the image.
The stars were removed by the StarnetV2 Gimp plugin. The stars and the starless images generated in the Gimp were saved.
The starless image was denoised in Neat Image and then stretched with Curves and Levels with contribution from Shadows and Highlights correction and Exposure black level in the Gimp.
The processed, starless image was then selective colour processed in Photoshop CS2 to reduce the green and increase the golden hues associated with the Hubble Pallete. Further denoising was done if necessary.
The stars image was processed with Hue-Saturation in the Gimp to reduce the magenta hue of the stars.
The stars were then added back to the processed starless image using the Screen mode with curves processing of the stars layer before flattening. The curves processing allows for the exact, desired contribution that the stars make to the final image.
Of course, there are a number of possible workflows that could have been used to produce the desired result using various software. However, this is the protocol that was used here.
The Rosette nebula
AstroDMx Capture capturing 5 minute exposures through the SII/OIII dualband filter
AstroDMx Capture capturing 5 minute exposures through the Ha/OIII dualband filter
The Rosette nebula in SHO the Hubble palette
The Wizard nebula
AstroDMx Capture capturing 5 minute exposures through the Ha/OIII dualband filter
AstroDMx Capture capturing 5 minute exposures through the SII/OIII dualband filter
The Wizard nebula in SHO the Hubble palette
The Flaming star nebula
AstroDMx Capture capturing 5 minute exposures through the Ha/OIII dualband filter
AstroDMx Capture capturing 5 minute exposures through the SII/OIII dualband filter
The Flaming star nebula in SHO the Hubble palette
The Elephant Trunk nebula
AstroDMx Capture capturing 5 minute exposures through the Ha/OIII dualband filter
AstroDMx Capture capturing 5 minute exposures through the SII/OIII dualband filter
The Elephant Trunk nebula in SHO the Hubble palette
The Heart Nebula
AstroDMx Capture capturing 5 minute exposures through the SII/OIII dualband filter
AstroDMx Capture capturing 5 minute exposures through the Ha/OIII dualband filter
The Heart nebula in SHO the Hubble palette
The Soul nebula
AstroDMx Capture capturing 5 minute exposures through the Ha/OIII dualband filter
AstroDMx Capture capturing 5 minute exposures through the SII/OIII dualband filter
The Soul nebula in SHO the Hubble palette
The Jellyfish nebula
AstroDMx Capture capturing 5 minute exposures through the SII/OIII dualband filter
AstroDMx Capture capturing 5 minute exposures through the Ha/OIII dualband filter
The Jellyfish nebula in SHO the Hubble palette
The Tadpole nebula IC410
AstroDMx Capture capturing 5 minute exposures through the Ha/OIII dualband filter
AstroDMx Capture capturing 5 minute exposures through the SII/OIII dualband filter
The Tadpole nebula in SHO the Hubble palette
The Horsehead and Flame nebulae
AstroDMx Capture capturing 5 minute exposures through the SII/OIII dualband filter
AstroDMx Capture capturing 5 minute exposures through the Ha/OIII dualband filter
The Horsehead and Flame nebulae in SHO the Hubble palette
The Altair 6nm Dualband Ultra filters Ha/OIII and SII/OIII allow proper narrowband imaging with a one shot colour camera and the use of only two filters instead of three. Moreover, more OIII is captured which facilitates the preparation of the OIII channel.
It is also possible to produce other bicolour palettes such as HOO and the much less known SOO palette.
The Heart nebula in SOO
The Soul nebula in SOO
The Rosette nebula in SOO
