Something a Little Different

Following on from my last post, I made the most of the clear weather that we had last week. Again, it was a little jaunt out with some of my fellow WolvAS members at our society observatory.

This time, it wasn’t with my scope, but just with my camera and tripod. Fortunately, we have a large oak tree directly north of our site, which made a nice foreground object for some star trail photography. It also makes it really easy to find polaris when I am with my telescope!

I originally started out with the 50mm F/1.8 ‘nifty-fifty’ Canon prime lens attached to my camera, which was great for the low F ratio, but not so good for the tight field of view. On my canon APS-C sensor, it’s more like an 80mm lens; great for portraits, not so much for wide angle landscapes. Regrettably, I had no choice but to swap to the kit 18-55mm lens. As the optics of the lens aren’t the best, I stopped it down to F/5.6 from the wide open F/3.5 to help tighten up the stars and reduce vignetting at the edges of the image.

To start off, I first focused the lens on the very bright Jupiter in the south. Any other bright star would do, but it was easily found in the viewfinder. Once the pin-point light was as small as I could make it in the live view screen, I carefully re-framed the camera using the ball-head on the tripod. To make sure I didn’t knock the focus position, I put the lens back into AF while moving about, making sure I flip it back to MF before I pressed the shutter. It was difficult to see my framing in both the viewfinder and in live view, so I ended up taking short, high-ISO test exposures to fine tune my composition.

Once I was happy, I started off with a higher ISO, but found the resulting images to be too noisy. Therefore, I dropped the ISO by half and doubled the exposure to compensate. I finally settled on ISO800 with an exposure length of 60-seconds, which gave decent amount of star trails, while still revealing some detail in the foreground. In the process though, I did take a series of 5-minute exposures that I could use as a replacement for the foreground. Became invaluable in the editing process!

One thing I did not anticipate though was the ferocity of the dewing problem, and throughout the night I had to wipe the lens multiple times. This made me disregard 36 exposures, meaning I could only stack 24-minutes in StarStax. I’ll need to invest in a dew heater if I wish to do Milky Way photography next year!

The stacking process caused the foreground in the exported image to be slightly blurred and duplicated in various places, most notably the tree in the middle. So within photoshop, I managed to layer the 5-minute exposure on top of the star-stack. Using the new 2022 version of photoshop, it was an easy process to remove the sky in the foreground layer. This allowed me to have a crisp foreground, as if the scene were taken on a full moon evening, instead of a moonless sky. It’s just a shame about the sky glow from Wolverhampton and the numerous planes dotting across the scene. I did try to remove the latter, but could never get it right without it noticeably leaving artefacts in the star trails, so just reduced them as much as could.

The resulting images is, in my opinion, a really good first attempt at trying star trails. I would like to re-try it again at some point with more exposures and a slightly different composition, putting the north celestial pole in the top left corner of the frame.

Till next time, wherever you are in the world, clear skies!

24-Minute Star Trails

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