Wide field astrophotography

By definition, ‘wide field astrophotography’ simply means capturing a lot of the sky in the frame, usually with a wide-angle lens. Small wonder it’s the most popular type of astrophotography with everyday photographers and is one area in which a regular camera and standard to wide-angle lenses come into their own. You can even use a smartphone camera in some situations.

This wide-angle shot of the Milky Way reflected in water provides a great example of the ‘scenic’ potential of wide field astrophotography. Captured with a Nikon D5 camera and a 20mm lens at its maximum f/1.4 aperture and multi-pattern metering, it was a 1/30 second exposure at ISO 3200. (© Andrew Murrell; source: Camera House.)

Equipment
To get started you need a camera and a tripod. If you use a smartphone, you’ll need some way to attach it to your tripod. Plenty of options are available, with prices ranging from less than $10 to almost $50. Many smartphone cameras include night modes that allow you to adjust exposure times and most can be triggered with self-timers.

Smartphone mounts are available for attaching your phone to the eyepiece of a telescope so you can record images with the phone’s camera. (Source: Camera House.)

Some cameras include dedicated ‘Star Trails’ modes, which work by compositing frames (see the Live Composite box on page ??). Some let you adjust ISO sensitivity and exposure times and for those that don’t, camera apps like Camera+ 2 for Apple and Camera FV-5 for Android give you some manual controls and allow you to save images as raw files (usually the ‘universal’ DNG format, which is widely supported in image editors).

This illustration shows a typical enthusiast’s set-up with a camera mounted on the eyepiece of a reflector telescope. Note the drive mechanism on the top of the tripod that keeps the field of view constant by counteracting the Earth’s rotation when tracking objects in the sky. (Source: Camera House.)

If you can piggyback your camera on a tracking platform – either as a separate tripod attachment or as part of a telescope – and if its resolution is 20-megapixels or more you’ll be able to record high quality images. Equipment like this is used regularly to monitor (and also discover) variable stars, novas, supernovas and exoplanets.

Because the Earth rotates, if you want the stars in the sky to appear sharp, exposures should be less than about 30 seconds. A star tracker moves your camera in sync with the Earth’s rotation and supports longer exposures.

Most trackers are driven by smartphone apps, which are usually available for Android and iOS operating systems. Some use AA batteries; others built-in rechargeable batteries, most of which support USB charging. Your local camera shop can show you what’s available and provide advice on which products are best suited to your requirements and equipment.

As far as lenses are concerned, your choice will be dictated by how much of the sky you’d like to cover in the frame and how long the exposures will be. Kit zoom lenses with focal lengths between 24mm and 70mm are adequate for starters, although they’re slower than equivalent prime lenses.

This single 15 minute exposure was captured with a camera that has an APS-C sized sensor, using the kit zoom lens at f/5.6 with a focal length equivalent to 16mm and ISO 100 sensitivity to minimise image noise.

Prime lenses are usually faster and are often cheaper because they use fewer elements in their construction. There’s a wide range of focal lengths to choose from and you can often find affordable prime lenses with much wider angles of view if you opt for manual focus lenses.

You seldom need autofocusing for wide field astrophotography since most images will be captured at infinity focus. Chinese manufacturers like Laowa, Meike and Samyang cater for all popular camera mounts and offer products designed to be ‘distortion-free’, an important feature to consider. They also make ultra-wide ‘fish-eye’ lenses with both rectangular and circular fields of view.

A head torch with a red light mode helps you see what you are doing in the dark. Red light is easier to dark adapt to than white light and also better for your night vision.

In really cold weather, you may need a hand warmer to keep your camera and lens warm enough to prevent moisture from condensing on the front element and blurring images. Hand warmers can also keep your fingers nimble when it’s cold.

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This article by Margaret Brown is an excerpt from Astrophotography pocket guide – click here to order print or ebook edition.

Pocket guide Partner: Camera House