DarKnights Field Trip 2nd January 2023: Windmill Field Star Trails

Our first DarKnights field trip of 2023 was a short notice visit to Windmill Field just north of Bracknell. Gladys had spotted a potential clear skies night on the app we use, and whilst it wasn’t “perfect” in the end it was good enough. Seven hardy souls braved the mud and freezing conditions to do some more experimentation with star trails.

In her recent talk to the Club, Caroline Colegate, proffered the advice that it is important to practice taking photos. Well that’s what this trip was all about – practice and learning. Whenever I speak about my role in the Night Photography SIG I also state that I am no expert. I shall show below the wisdom of Caroline’s advice and my own self assessment!

The purpose of our evening was to take forward the learnings we had made back in December when shooting star trails at Cabbage Hill. In this instance we wanted to add some simple foreground interest and for this the very nicely shaped oak tree in the middle of Windmill Field served its purpose.

My goals

I had two personal learning goals. I felt that I had been underexposing my Astro shots for most of last year and as a result when I started to increase exposure or shadows in post processing I was introducing a lot of noise. In addition probably my skies were a very uninteresting and “muddy” black. So I was determined to let more light into my camera (which in fact was helped by a half moon illuminating our foreground subject quite well). Secondly I wanted to see how far I could push the interval between images so as to minimise the number of photos I would need to process and stack later.

I therefore commenced with my usual set up routine:
• Compose the shot: in this case it was easy, oak tree dead centre and pole star (the centre of the rotation) above it – I missed slightly by the way!
• Next focus. The lens I use has a massive depth of field so it is relatively easy to focus on the brightest stars and get a foreground object 20 yards away in focus to
• Then exposure: I followed my normal practice starting with f2.8, about 5 seconds exposure and a relatively high iso. But this time I followed my own advice and looked at the histogram/believed myself that the image on the back of the camera was brighter in the dark than it would appear at home and produced an exposure (with test shots) which almost looked “over exposed”. I then recalculated the ISO based on a shutter speed of 15 seconds which was the maximum I wanted to go to. Thus I was shooting at ISO 640 – it was quite bright because of the moon – I did hear it mentioned that someone even used ISO100 and Steve Buesden used 50 (see below)

I’m quite satisfied with this workflow and the end result for the single shot shown below:

However, I discovered that I had extended the interval between my shots too much. I was allowing 25 seconds between the shutter closing and then opening again. This has resulted in the star trail being too “gappy” giving it a juddery appearance (you can actually correct that in post, but that’s more complication). In addition because in the end there were some mid- to high- level clouds on the evening which were actually blowing across quite quickly, you can see that I actually have a “banding” appearance as they moved between frames.
The first photograph below is using the first 70 images I took all compiled in PhotoShop. I left all the plane trails in too, which actually I quite like in this instance. But I think it looks awful with the clouds.

This second photograph has eliminated the layers containing most of the planes and tried to eliminate the impact of the moving clouds…but note now that my star trails really are not very epic.

Just out of interest I did stack all 70 frames in one go in PhotoShop (from Lightroom) and my mid-range MacBook Pro coped well with processing them (nearly 10GB file) in about a minute. I was impressed.

Steve Buesden’s image

Several participants have shared their images on the private club Facebook group  but I would like to use Steve Buesden’s composite image to contrast the learning from my own. Steve tells me this is his first attempt at this type of image so nice one! This image was from a total of 170 frames taken at 30s but crucially with only 1 second between shots- I have to say this gives a much smoother star trail, has (in my opinion) smoothed out the cloud flow and allowed him more room to clone out the planes. For perspective he also was able to shoot at ISO 50.

Conclusions

Steve and I were on the location for roughly the same length of time but he has at least twice as many images as me. This was my final learning of the evening. We all realised that our lenses were misting over – actually icing over. I proudly produced my newly purchased lens warmer and fitted to my kit. This worked well and I had no misting or icing (unlike my tripod!) – but what I failed to notice is that I had moved the focus ring ever so slightly and ended up with 70 out of focus shots. Very annoying, but a good learning to put that on at the start and NOT to touch the camera again!

So there we go. I’m no expert and Caroline is right – keep practicing. Talking of which, everybody seemed to enjoy the evening I would propose to keep running some very local and last minute, weather-dependent field trips like this so we can continue to refine our skills.

I have a couple of ideas for field trips to further afield (such as the one to Wilton Windmill that we had to cancel due to bad weather). These will be announced to all Club members so everyone can join in with the DarKnights!

Gareth Fish
DarKnights SIG leader