Today was the transit of Mercury 2016. I had two set-ups today – my Coronado Ha PST telescope with my ASI120-MMS camera in it and my Meade 127mm refractor with a white light filter on it, on this scope I tried my Atik 460 and Canon DSLR but none of these images came out that well, these cameras are just not made for solar imaging, all images from these cameras were too bright.
I imaged the transit of Mercury with the PST on its own and with a Televue 2.5x Powermate. The problem with the PST is that it does not do well when trying to image the whole of the solar surface as the etalon does not cover the whole of the solar disc so you can get bright and dim areas of the surface. The Coronado PST works best with the Televue 2.5x Powermate.
Previously I used a lot of the Imaging Source DMK CCD cameras, and I never really suffered from Newton’s rings. Thing is now I have an ASI120 camera which is a CMOS camera, it does seem to suffer badly with Newton’s rings. When trying to remove the rings it seems you can either buy a tilt adaptor or take flat frames.
I have always taken flat frames for deep sky imaging, but never for solar, lunar or planetary imaging. I did try taking some dark frames to remove the Newton’s rings but that never worked. Taking flat frames does work though.
I only tried taking flat frames when I took zoomed in images of the Sun with the 2.5x Powermate. You begin taking your normal video and then keep all the settings the same but just de-focus your telescope and then take a video of exactly the same length of time.
All the work is then carried out in AutoStakkert. Begin by loading your video of the de-focused Sun and select “Image Calibration” > “Create Master Frame” – then you will be asked to name the TIF file. Once completed you can then select “Image Calibration” > “Load Master Flat” and load your TIF file. Then load your AVI or SER video file and process it normally. You will now see all your Newton’s Rings disappear and your dust bunnies or doughnuts will also have disappeared.
It’s a pain to keep having to remember to take flat frame videos all the time, but as long as you don’t change your field of view or exposure, gamma or gain settings you should be OK and be able to use the same flat frames.
Mercury on this is at the top right hand corner, taken very close to first contact.