Tuesday 24 January 2023

Astrophotography - attempt 1

I've been interested in astronomy since childhood, and spent a large chunk of the money I earned working during vacations while I was a uni student in the early 1980s on a Meade 10" telescope (I previously had a 4.25" Tasco reflecting telescope during high school, that my mum bought me as a birthday present - it wasn't cheap but wasn't particularly good quality). Despite having invested a considerable amount of money (around $5K for the telescope, lenses, solar filter etc - which in the early 80s was about 1/20th the cost of a three bedroom house!) I didn't actually use the telescope very much. More recently (early 2000s) I bought a Meade DSI monochrome CCD camera, but had trouble using it to take any astrophotographs at prime focus, so gave up again. Then, a few years ago, I bought a Nikon D3300 DSLR camera to use while on vacation in New Zealand, with plans to also use it for astrophotography. Yesterday was a clear night, so in preparation for trying to take some images of Comet C/2022 E3 (ZTF) when it is visible close to Mars in the southern skies around 11 Feb, I setup the camera on a tripod on our front porch and took a set of 90 x 2 second exposures (total 3 min exposure) of the Orion constellation using the 18-55mm 'kit' lens at F/3.5 and ISO set to 12,800. I also took a set of 45 matching 'dark' frames and a set of 45 1/4,000th second 'bias' frames and 45 (badly overexposed) 1/15th second 'flat' frames, which all were then processed/stacked using the free software SiriL.

I was pleasantly surprised by the result (in parts) of my astrophoto, with the region near the M42 nebula in the Orion constellation being recognizable, and of roughly comparable (OK, mine is a lot worse) quality to a similar photo taken in 1890 by the Government Astronomer at Sydney Observatory using a 6" portrait lens on an astrographic camera with a 4 hour long exposure.

But despite the region around M42 being 'OK' in my image, the overall image was rubbish, with a lot of 'flare' being apparent. I think I had two major issues: 1) I didn't check the histogram of the 'flat' images taken using a 'white screen' on my tablet, so ended up with vastly overexposed 'flats', and 2) I didn't put on the lens hood that came with the 18-55mm zoom lens, so may have ended up with 'flare' due to light from a nearby streetlight getting caught by the lens. Next clear night I'll repeat the exercise, but try a more zoomed in view (55mm) and properly exposed 'flats' (and the lens hood!).

One good thing about astrophotography as a hobby (once you have bought the equipment) is that it is cheap to do -- you just recharge the camera battery and delete the files from the SD card and you are ready for another night of imaging.

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