Sunday 12 February 2023

Astrophotography - attempt 3 - comet E3 conjunction with Mars

I had planned to drive out to a nearby 'dark' sky site (slightly less light pollution than where I live), but due to intermittent cloud cover I decided to just wait at home and when there seemed to be a break in the cloud cover I took 180x3 second exposures )using my 55-200mm zoom lens at 55mm, F/4, ISO 12,800) from my front balcony, with the camera in a corner where the glare from a nearby street lamp was blocked from directly hitting the lens. I also took 50 'dark' frames (3 sec with lens cap on) and 50 'flat' frames (using some white cloth in front of the lens illuminated using my tablet, and Automatic exposure length), and had planned to take 50 'bias' frames (1/4,000 sec exposures) but the SD card was full after taking 34 bias frames. There was still probably some light cloud cover passing overhead, but none of the lights showed obvious cloud cover, so I didn't discard any of the images from the stacking process. A car also drove past and turned on a floodlight across the street, so I expected 4-5 of the lights would be ruined, but I couldn't see any obvious problem images (although the final result could probably be improved by eliminating some of the light frames that were affected by cloud cover or the car/floodlight glare -- but I'd need to run through the pre-processing manually to do that).

I did automatic pre-processing using the standard script in SiriL, and then saved the resulting image as a jpg and did some rudimentary brightness and contrast tweaking in GIMP (although I don't really know what I doing and just played around with some settings).

At least in my 'final' image you can tell the comet E3 is in close conjunction with Mars, so I'm happy enough with the result. At least I managed to get the stars reasonably in focus this time! Usually with exposures taken over a period of around 10 minutes the comet would have moved compared to the star field, so some fancy processing to register and stack the stars and then separately register and stack the comet with the stars removed from the image would be required. But there doesn't seem to be too much movement/blurring of the comet in my final image - not sure if it is because the comet is now on the way out from the sun and its apparent angular motion has reduced already, or just due to the relatively short total time period during which the lights were taken.

Anyhow, I took my first astrophotograph of a comet, and the result is at least recognizeable. So I'm happy.

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