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Photographing the night sky

  • Written by  Keith Wilson
  • Published in Geophoto
Photographing the night sky
07 Feb
2019
Few sights are more dramatic than a star-filled sky at night. But to capture it in all its glory, you need to get far, far away, says Keith Wilson

The long nights of winter are the best time of the year for observing the stars and constellations and particularly the band of subtle starlight that constitutes the Milky Way. But it requires more than a clear, moonless night to observe this celestial phenomenon, let alone embark upon any attempt to photograph it.

Unfortunately, light pollution from street lamps, floodlights, motorway illuminations and other artificial sources make it extremely difficult for any urban dweller to see more than the light of the moon or our neighbouring planets of Mars and Venus. But our chances improve dramatically when we head out of the cities to unlit areas of countryside, or better still, to the open waters of the sea. The best evenings are those that are free of cloud and as far as possible from the date of a full moon, as the bigger and brighter the moon, the fewer stars you will be able to see. Check the lunar calendar in advance and the latest weather forecast to improve your chances.

DARK SKY SITES

The British Isles are home to three large dark sky areas (DSA) designated by the International Dark-Sky Association (IDA), where light pollution levels are deemed sufficiently low to enable ideal viewing of exceptionally starry skies. These are the Galloway Forest Park in southwest Scotland, Exmoor National Park in Devon and Somerset, and the Channel Island of Sark. By attaining DSA status, these three locations have become favourites for photographers specialising in spectacular nocturnal landscapes. At 780 square kilometres, Galloway is home to the UK’s largest forest park with a variety of scenery including heather-clad hills, lochs and mountain slopes, as well as forest plantations to frame the night sky. The moorland and ancient monuments of Exmoor provide a dramatic foreground for the stars, while Sark offers unblemished views over its rugged coastline.

In addition, there are 17 Dark Sky Discovery Sites in the UK, including locations within the Brecon Beacons, Snowdonia, South Downs and North York Moors national parks, as well as the Elan Valley in mid-Wales, Kielder Water in Northumberland and the Isle of Coll. Astronomers have capitalised on these conditions by erecting a number of observatories, most notably at Dalby Forest in the North York Moors and Kielder Observatory in Northumberland. Designated dark sky sites are spurring greater interest in astrophotography. In September 2018, Exmoor-based company, Dark Sky Destinations, launched its first ‘nightscape astrophotography’ course designed primarily for those attempting this type of photography for the first time.

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EQUIPMENT ESSENTIALS

Once you have chosen your dark sky area (a full list of designated areas can be found at www.darksky.org) and a suitable date with favourable weather conditions, all you need for your astrophotography venture is a DSLR or mirrorless camera with a wide-angle lens, a tripod and a compass, which will help you to orientate. An alternative is to use a compass app on a smartphone, but looking at bright screens hampers your night vision and it can take up to 20 minutes for your eyes to fully adjust.

Of course, stars in the northern hemisphere skies are visible all year, but some clusters and constellations are easier to recognise at particular months. The Geminid meteor shower is more visible during winter, spring is better for viewing the planets and autumn is prime time for observing the Orionid meteor shower. Although the Milky Way is huge, it isn’t always visible to the naked eye and it is necessary to first establish in which direction to point your lens. The easiest way is to use another smart phone app such as Star Walk 2 (www.vitotechnology.com). This can pinpoint the galactic position in real-time or for a future date. 

A WIDE VIEW

Having worked out the direction, a wide-angle lens is the best choice to capture the vast expanse of the Milky Way and to let in as much light as possible. Focal lengths of between 20mm and 28mm are ideal for this purpose, with the aperture at its widest setting – typically f/2.8 with these lenses. The camera and lens need to be secured to a tripod, with the legs firmly in place – push down gently on the tripod to check this as it’s essential that there’s no hint of vibration or movement during the long exposure time that is to follow.  Your chances will be further improved if you have picked a still night.

When composing the picture, it may be tempting to fill the frame with only the night sky, but a more pleasing image is usually achieved by adding context to the scene through the inclusion of an interesting foreground. Because many dark sky areas are situated in photogenic locations such as hilltops, national parks, high moors and lake shores, finding a suitable foreground needn’t be a difficult exercise. A horizontal aspect with a foreground that fills the bottom quarter or third of the frame will provide a pleasing counterbalance to the starry sky above. If your aspect of the Milky Way includes a lake, mountain tarn or the sea in the foreground, then there is the potential to include a reflection of the starry sky on the surface water below.

Although most photography is done with autofocus, this is one occasion when it needs to be switched off. When it comes to far-off constellations and galaxies, we are focusing, to borrow a phrase, ‘to infinity and beyond’! In this case, the focus distance of your lens will remain set on infinity.

OPEN SHUTTERS

The most critical part of a night sky exposure is to have the shutter open for long enough to render the Milky Way and other stars within your frame in all their spectacular brilliance. There are key settings to follow to achieve this: setting the exposure mode to aperture priority, choosing the widest lens aperture value – typically f/2.8 – and cranking up the ISO setting as far as it goes – say ISO 25,600 or higher. This will ensure your camera shutter remains open for as long as possible. Always treat the first exposure as a test shot to check the overall exposure and resulting noise levels, as well as the composition.

You should expect long exposures of 15 seconds or more using this technique, in which case you need to use a remote shutter release to fire the camera shutter, or select the camera’s self-timer or exposure delay mode. In practice, exposures longer than 30 seconds will begin to render the stars as elongated lines due to the Earth’s rotation. Of course, if you want to emphasise this effect, then try a number of frames at ever-increasing exposures of several minutes or more. Remember though to reduce the ISO setting accordingly for every stop increase in shutter speed.

It is worth bearing in mind that the longer the exposure time, the greater the chance for a single line of light from the passing trajectory of a satellite, or the blinking lights of a passenger plane entering your frame. Also worth noting is that during long exposures it is possible for stray light to enter the viewfinder and ‘leak’ into your shot. This can be avoided by flipping down the built-in viewfinder blind (should your camera have such a facility), or by simply attaching the eyepiece cover.

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BACKGROUND OPTION

While the Milky Way has been observed here as a subject in itself, some photographers take a different approach by featuring it as a backdrop to another subject of their choosing. Landscape photographers are utilising the vastly improved image resolution obtainable at very high ISO settings to photograph prominent landmarks such as desert arches and mesas, canyons and gorges at night. The combination of a high ISO setting and long exposure has enabled the iconic landscape vista of daylight hours to be viewed in its nocturnal guise, but with the startling addition of a background sky filled by the Milky Way. 

Even wildlife photographers are using the same technique to add a new perspective to well-known species, but this time with the addition of flash fired remotely (or with an infrared trigger), when the intended subject wanders into frame. The shutter continues to remain open to record the ambient light of the background stars and galaxies. 

At this time of year, the high ISO, long exposure technique can also be applied to another celestial subject that has become more popular in recent years – the aurora borealis, also known as the northern lights. Auroras are caused by solar storms when clouds of fast moving, highly charged ions are trapped by the Earth’s magnetic field and forced down into the atmosphere. When the ions collide with atmospheric gases, they start to glow and produce these extraordinary light shows.

The best time to photograph the aurora borealis is in March and April, as it isn’t as cold as the midwinter months but still provides plenty of hours of darkness for photography. The part of the northern hemisphere where the northern lights are most visible is known as the ‘auroral oval’, which extends over northern Scandinavia, Alaska, Siberia and the whole of Canada. Sometimes, aurora sightings extend further south to the northeast United States and even into central Europe. If you master your technique for photographing the Milky Way this winter, then you should be ready for the aurora borealis come March.

This was published in the February 2019  edition of Geographical magazine

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EQUIPMENT SELECTORS

ZPR NIKON Z6 FRONT 24 70

CAMERA: High ISO models
The recently launched Z6 is the second in Nikon’s new Z-series range of mirrorless interchangeable-lens cameras (£2,100 body only). Its more expensive brother, the Z7, may have the larger sensor, but at 24.5 megapixels, the Z6 is no slouch. Furthermore, the Z6 has a higher ISO range of 100-51,200, expandable to an incredible ISO 204,800, which makes it the better choice for shooting the night sky. Added to this is a tilting, touchscreen LCD monitor, convenient when used in a fixed position on a tripod for long exposures.
www.nikon.co.uk

sigma 24mm f 1 4 dg hsm 1120085

LENS: Fast wide-angle

A high quality wide-angle lens with an extra wide ‘fast’ maximum aperture is the ideal lens for photographing the Milky Way. Fixed focal length prime lenses are desirable because they have a larger maximum aperture than their zoom lens equivalents. The Sigma 24mm f/1.4 DG HSM Art lens (£620) is a perfect example. At f/1.4, that maximum aperture is a mighty stop and a half greater than many cheaper f/2.8 wide-angles, which means it can gather more light from the starlit skies. It costs more than many other 24mm lenses, but the optical quality is hard to match.
www.sigma-imaging-uk.com

manfrotto mt055cxpro3 carbon fiber tripod 1034140

ACCESSORY: Robust tripod

A carbon fibre tripod is less conductive to the cold while still as lightweight as aluminium. The Manfrotto MT055CX PRO3 (£320), is a prime example that uses clip-locks for adjusting. There is a 90° pivot system for the centre column, which is ideal for use with wide-angle lenses.
www.manfrotto.co.uk

DO’S & DON’TS

Do...

• Choose a recognised dark sky area. Choose a date away from a full moon and listen to the weather forecast, looking out for a clear, still and cloud-free night.

• Fix the camera securely to a tripod and ensure the standing surface is as stable as possible. If your lens or camera has an image stabilisation or vibration reduction facility, switch it off.

• Use a wide-angle lens to capture the vast expanse of the Milky Way and to let in as much light as possible. Focal lengths of between 20mm and 28mm are ideal for this purpose.

DON’T..
• Use autofocus. After all, the camera-to-subject distance for stars is infinity, so switch off the AF to stop your lens from ‘hunting’ in and out of focus and instead turn the manual focus setting to infinity.

• Press the shutter button with your finger. Instead, use a dedicated remote release or the camera’s exposure delay mode to fire the shutter.

• Make exposures longer than 30 seconds. Keeping the shutter open longer than this will begin to render the stars as elongated lines due to the Earth’s rotation.

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University of Winchester

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