AstronomyWood: Going to the dark side

Otherwise known as using a mono camera with narrow band filters.

My location is a Bortle 7 or 8 class location dependant upon which app you use. This means I have heavy light pollution from lots of sources. When using a one shot colour camera (OSC) or DSLR camera I use either an IDAS IGAD LPS-D2 or Altair Astro Triband filter. The former filters out light pollution including LED street lamps which are prevalent in my location leaving a very decent RGB image. The latter does the same but filters out everything apart from Hydrogen alpha, Oxygen III and Hydrogen beta.

IDAS LPS-D2 filter works great on LED street lamps

Altair Astro Tri-band Filter

Obviously with a OSC camera you have to take longer exposures, more exposures or a combination of both to acquire enough data to be stacked. This is due to the Beyer colour matrix of RGGB covering the monochrome sensor.

However in a purely monochrome camera you have no Beyer matrix to contend with and consequently due to this lack of colour filtration on the chip you have 4 times the sensitivity to light. All you have to do is filter out the wavelengths you don't want and the sensor can be used to capture the light you do.

Step forward the ZWO ASI 183MM, ZWO EFW electronic filter wheel and a set of narrow band filters. In my case the ZWO 7nm Mark II set of 31mm unmounted NB filters. Not the best but if you are on a budget they are fine and produce good results.

ZWO ASI183MM Pro cooled dedication astronomy camera

The filter wheel and filters came first as they were in stock from two UK astronomy suppliers, Widescreen Centre in Ely, Cambridgeshire and FirstLightOptics in Exeter, Devon respectively. However due to the Covid19 induced manufacturing problems affecting deliveries from ZWO in China the camera came several weeks later from Telescope House.

ZWO ASI EFW5 5 position electronic filter wheel

Fitting all the bits together was a doddle as all the parts are included in the boxes from ZWO.

After the inevitable clouds for a few weeks first light was on August 30th 2020 and I managed to image the Crescent Nebula in Ha. I got a good quantity of subs and the camera was set at default 111 gain and 8 offset.