2017 07 07 -Just One Click – Botallack Star Trails pt1 - Adam Sherratt

2017 07 07 -Just One Click – Botallack Star Trails pt1

Welcome to the first of what will become a series of articles where I take you behind the camera and into the making of the photograph. I will share with you my thought process behind the framing and composition, the elements that I was looking for to tell a good story. We’ll look at some of the processing techniques that I use to bring the photograph from the RAW file to the finished article, from simple masking through to luminosity masks and some of the more advanced techniques.

In this first article I wanted to take you through the making of this “Star Trails” or “Star Stack” photograph, taken at Botallack Mine in Cornwall, from how I selected the location, to the camera set up, all the way through to the creating of the final photograph that you see below. The shot is made up of hundreds of photographs, each stacked on top of each other and blended in Adobe Photoshop. What you are seeing is the rotation of the Earth relative to the stars in the sky, as the earth spins on its axis. In part one of this article I will talk you through how to select the location and set up your camera. In part two, I will show you how to process the photographs that you have taken.


A star trails photograph of the Botallack Mine in Cornwall. This location features in the BBC TV series Poldark

On Location

For star trails shots to work, the photographer needs to give an “under the stars” feeling to the viewer. By this I mean that there needs to be a clean, simple foreground that the viewer can instantly relate to. Why is this important? The star trails in these shots are very dominant, so vibrant and unusual meaning the viewer will clearly focus on this area of the photograph. Therefore we need to make the foreground simple, less complicated, and easy for their eye to access.

Your location needs a clear line of sight to the North Star. In the Northern Hemisphere the North Star is a fixed point in the sky. As the earth spins on its axis, that star remains fixed in the sky, while all of the other stars change position (well, they don’t, we do!), giving the twist effect that is the key to the star trails photograph. So you should take up a position where you can frame your choice of foreground, looking North, with the camera angled in such a way that the North Star is in the shot. You can choose to have it offset, or perhaps directly above your foreground main element, depending on whether you want the stars to spin in the corner, or almost around the object.

The next thing to consider is your safety. You will be on site after dark for several hours. You need to select a site where there isn’t going to be much light interference (cars headlights, boats, planes) so you are likely to be in a remote area. You will need to plan your route home, making sure you have a torch, but also plan to be on site for several hours as the temperature drops. A flask, a good coat and a chair are recommended!

The images below show you how to find the North Star in the sky, as well as a quick diagram showing the elements discussed above against my Botallack Mine shot.


Follow the imaginary line from the two stars in Ursa Major to get to the North Star

To find the North Star, Polaris, first find the constellation Ursa Major (The Big Dipper or the Plough) and then draw an imaginary line from the last two stars in the “Bucket” through to the brightest star in the sky, this is the North Star.


This image shows the various elements of the Botallack Mine photograph

You can hopefully see the story behind my shot. The Botallack Mines are part of the UNESCO World Heritage Site covering the Cornish and Devon mining industrial sites. The mines here are from the 1800’s however mining at this site is thought to date back to the Romans, and possibly beyond into the Bronze Age. I wanted to show the passage of time against the ancient mine head buildings, standing under the stars for hundreds of years, constantly under attack from the sea and the weather.

The main difficulty with this composition is that it is impossible to frame the mine buildings against a clear background because of the cliffs behind, but I knew I could make them more prominent in post processing. I wanted to show the sea, but didn’t want to much as it would be very dark, dead space in the image, so opted to frame just the area where the sea crashes against the rocks. I also wanted to give stars space in the frame to give lots of movement.

So, in summary, when choosing your location you should:

*Select a simple but strong foreground element

*Accept and plan for the fact that the stars will dominate the image

*Select a north facing view point

*Identify and frame the North Star

*Plan for a long, cold night!

*Stay safe!

The Shoot

There are two methods for shooting star trails. The first is to take one incredibly long exposure, minutes, if not hours, long. The earth rotates, the stars “spin”, and you have your shot. However this method while simple gives worse results. The sensor in the camera heats up, causing noise which will ruin the shot. You also have the problem of balancing the exposure for the foreground and then the sky.

The second, more reliable and successful method is to stack a series of photographs, little slices of time that when overlaid and laminated together give the whole story. This is the method that I will discuss below.

Equipment

*Camera Sturdy

*Tripod

*A compass/Star finding application (e.g. Stellarium)

*A timed remote shutter trigger (Intervalometer) or in camera timer. My Sony A7Rii has a built in app for taking time lapses, which works perfectly for this.

*Wide angle lens – 16mm f2.8 if you have one. If not, as wide as possible with as large an aperture as possible.

*Advanced- Dew Heaters

*Advanced – external power supply

You will need to check the weather forecast. You need a night where there is to be no cloud (or very little cloud cover). It needs to be dry, and preferably a slight wind (to prevent dew building up on your equipment). If your forecast app is accurate and detailed enough, check the dew point temperature, and compare that to the likely air temperature at your location. So long as the air temperature is above the dew point you will be ok.

Method

The shoot comes in two parts, however you will only use one framing, it being essential that the camera doesn’t move throughout the shoot. You will need to be on location around sunset so that you can set up safely and be ready to take your foreground shot while there is still some light around. This gives you the problem that you can’t see the stars, which is where a compass or star finding app for your phone comes in very handy. I use Stellarium, which shows you where the stars will be at a certain time of night, so you can plan ahead. Stellarium is available on the PC, iPhone and Android.

Set up

*Set up your camera on a very sturdy tripod, framing the foreground as you want it, ensuring the North Star is in the shot with room to spin.

*Set the lens wide – wide field of view, and wide open aperture.

*Set the camera to manual focus. This is important as you don’t want it to be focus hunting in the dark every time you try to take a shot.

*Turn off the long exposure noise reduction. This is very important, else for each 25 second shot, your camera will take another 25 second “dark” shot, giving you half the number of exposures, and potentially gaps in the star trails.

*Attach your intervalometer. This is a remote control for your camera that plugs into your remote input port (or is wireless). It basically acts as a timer, asking the camera to take a photograph at a certain time interval. You don’t need it for this next stage, but you’ll probably want to get it ready for later on. Set the interval to be 30 seconds, so that it triggers the camera once every 30 seconds.

*You preferably should be shooting in RAW mode to give the best results.

*Advanced: If you are using Dew heaters (strips of fabric with a built in heater to prevent the build up of dew on the lens element), attach them now. Also, if your battery life isn’t great, you may want to attach an external power supply to your camera. You don’t want to be changing batteries half way through a shoot. I use an Anker 25000 mah USB charger for my camera, which will power it for days!

Shoot the Foreground

After the sun sets and the day begins to turn to night, we being to take our foreground shot. I choose to shoot several shots at this time because there is still enough ambient light for there to be contrast in the foreground, which is important for the definition of the objects. You will need to focus on your foreground at this point, so carefully adjust the lens ensuring that you don’t move the framing. You can adjust the aperture for a sharper foreground if there is enough light, but ensure that the exposure doesn’t need to be too long (it is dark afterall) as you will get noise and potentially unwanted movement in your foreground. If your tripod is sturdy enough that you can be sure that you won’t move it by playing with your camera settings, it is worth taking shots at various exposure lengths and apertures. We’ll select the best shot in post process. You are looking for a shot that is dark enough that it won’t look odd against a dark sky, but light enough that the foreground is visible. Its a fine balance!

Shooting for the stars

Once you have your foreground shot, you need to set up your camera ready for the star shots. Set the aperture to as wide as it will go (f2.8 if you can) so that you get as much light in as possible. Set the ISO to the maximum that experience tells you your camera can shoot without too much noise, for me this is generally around ISO 3200. Then set up for 25 second exposures. These are generally the settings that I use, to maximise the light (and so the stars) while maintaining minimal unwanted noise. The 25 seconds is well within the intervalometers 30 second interval so there is no danger of missing a shot. Adjust the focus to infinity. This is generally marked on the the lens, with some lenses offering a “hard stop” on the focus ring at infinity. If yours doesn’t have these marks, just focus on something very far away! You can now sit back and relax for a while, until it gets properly dark.. Not the blue hour dark, but black dark. If you start shooting too early, you will get a lot of blues in the sky, which will add a colour cast to your trails when you stack them later. See the image below that demonstrate the differences in the light, taken just half an hour apart.


There is a 30 minute difference between these two photographs, showing the importance of waiting for true darkness So now that it is dark, you can start the star trails shoot. To recap, you have;

*Focussed on the stars

*Set the camera to f2.8, ISO 3200 and 25 seconds exposures

*Your intevalometer is ready to go

*You have switched off Long Exposure Noise Reduction

*You have attached your Dew Heater and external power supply.

Start the intervalometer running, and your camera will begin taking 25 seconds long shots of the stars. One will finish, the next will begin. You will need to shoot for as long as you, your camera, and the weather can sustain. The minimum number of photographs that you should take is 100, but aim for around 300. If you are up for it, shoot all night! The more shots you take, the more movement you will see. Its as simple as that. 300 shots will be 2.5 hours of photography.

Start the shoot going, and settle back. Keep light pollution from torches and mobile phones to a minimum, even behind the camera, and take care not to knock the tripod. Enjoy the night sounds, and the steady repetitive click of your camera. Make a mental note of the position of the stars as you start to shoot, relative to your foreground. You will clearly see them move over the time you shoot. This movement is what is making your star trails.

While taking the sequence, have a periodic check for dew building up. If you lens gets a coating of dew you may as well give up. Wiping it won’t make any difference, it will be back within minutes. Your shoot is, unfortunately, over.

Once you have taken your shots (2 – 300), you can pack up. Have a good scout around for equipment that has wondered off in the night! Go home and go to bed!

The morning after the night before

Your next job will be to process the photographs that you took. This isn’t a difficult process, but will require some knowledge of Adobe Photoshop and a fairly hefty computer. This process is discussed in part two of this article.


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