After a day or two longer than four months the sky cleared, for a bit anyway and I did some imaging, that’s crazy – a third of a year between imaging sessions because the sky is cloudy, raining or the air is misty or foggy or just plain rubbish. It’s December and I’ve been in a Tee shirt for heavens sake, anyway back to the imaging, I chose IC405 – The Flaming star nebula in Auriga.
To capture my images I use a nice bit of software called Astro photography tool, it will control the camera, focuser, filterwheel as well as guiding and has a host of usefull features such as bahtinov focus assist and Plate solving to name just a couple, and as with most software it has regular updates when new features are added, great. I started using APT with version 3.52, updating when a new version comes out and during the four months of doing nothing I’ve updated to version 3.81, so last night was the first time using the new version, this update has native support for ZWO cameras and when I connected the ZWO asi1600mm Pro camera I use, naturally I selected ZWO camera from the select camera type window, all good.
Before the update the camera was controlled by the ASCOM driver, ASCOM is the industry standard for astronomy software and it ensures that image aquisition, planetarium, guiding and other astro software are compatible and work together, however some ASCOM drivers are limited in their user adjustability and so camera manufacturers have started having their own native drivers with selectable options, again all good.
I managed to capture five shots of IC405 before ( yes, you guessed it ) the clouds rolled in, so while I waited for them to go away I processed the five images I had, for this I use another bit of software called Deep Sky Stacker to stack the images together after subtracting ” Dark frames ” so as to remove noise from the image, these dark frames I have stored in a Dark Library. first you have to load your images as light frames, then add your dark frames taken with the same camera, same exposure, same binning factor and at the same temperature This is not a problem as I always run the camera at -20 C ( camera noise is very dependant upon camera temperature ), when it’s done you have a nice image to work on in Photoshop for example. However DSS threw up the message that the images and darks were incompatible ?, upon checking the image data for the lights and darks I noticed that the image sizes were different by 4 pixels and this was causing the incompatibility, the image size of the asi1600 camera at 4x binning is 1164 x 880 pixels, this was the size of the darks, however the lights had an image size of 1160 x 880 pixels ( 4 pixels narrower ), how could this be as both the lights and darks were taken with the same camera ?.
It turned out that the native ZWO driver was causing the problem, when I switched back to the ASCOM driver and took an image, the image size was again correct at 1164 x 880 pixels, I’ve informed Ivo at APT and I’ll keep using the ASCOM driver till a fix is sorted. Anyway heres the result of four months worth of waiting, an uncalibrated image made from 5 x 5 minute exposures. Oh and by 11.30pm the sky had still not cleared so I called it a night.