A stack of stars

An ambition of mine for a few years so has been to have a go at doing some astrophotography.

Our holiday flat in Finisterre had a balcony with good views of the sky. I had all me gear with me, including tripod, Pentax K-70 DSLR with its moving sensor and 'Astrotracer' feature, the Pentax O-GPS1 hot-shoe mounting gps unit and a remote shutter release.

The only problems were that Finisterre seems to be the most fog / sea-mist prone place I've known, and secondly the totally inexperienced klutz operating the equipment.

Because the stars move, relative to the Earth, exposures have to be short if stars are to be points of light and not streaks. Because stars are relatively dim however, a short exposure won't catch much starlight. So the stacking technique involves taking quite a few shots of the same piece of sky, then using software to stack them on top of each other. The light from each star, which will appear in all or most of the exposures, is mutiplied. Meanwhile any random noise appearing in single exposure is diluted. An exposure with the lens-cap on is also included in the set for processing. Any spots of light appearing in that one are considered to be sensor  generated and are removed from the final image by the stacking software.

The Pentax is particularly suited to astrophotography because the moving sensor which, together with its astrotracing feature, means the sensor will track the stars for a short while, allowing for a exposures several times longer than with other cameras.

Given the mist I didn't have many clear skies. When I did have them I had difficulty figuring out how get the camera's timer to work as I needed it to. Often, just as I thought I was all set, I'd find clouds had rolled in. Eventually think I managed to take a couple of series of 45 second exposures, only to discover that the for the first series I had the camera set to JPG only instead of RAW, hence losing a lot of detail. The second time, I thought I had a good set, until I realised I'd forgotten to set the camera focus to infinity. I think it was quite an achievement that I managed to remember take the lens-cap off!

When I got home from the holidays however, going through my photos, I discovered that I did have a decent set after all. I think it must have been a quick practice that I had forgotten about.

So then I had to do some boning up on stacking software. I plumped for the free 'Sequator' software. After a bit of trial and error I managed to get this result from stacking, albeit with quite a bit of background noise which I was easily able reduce using Affinity Photo.

Towards the bottom of the image, just left of centre, is part of the constellation Cassiopeia.

I hope to do some more astrophotography my main problem is living in the city with it's light pollution. I still need to find an accessible location away from the city lights, but not too far away to be able to get to quickly when the sky is clear.

Thanks to blipper RainerSheinp who has recently posted his first stacked star image. It prompted me to get mine blipped as well.