Out of this World

What is involved in taking images of the night sky? In the April-June 2011 issue Nick Howes showed us how simple it can be, whilst sharing some of the more advanced techniques for capturing constellations and galaxies.

You'll be glad to hear that you can use any EOS model to shoot astro images. Many budding Hubble wannabes start out on the interchangeable lens camera route, progressing through more sophisticated models until they move on to dedicated astro imaging cameras.

Take heart that with your EOS camera you already have one of the most respected products in the astro imaging domain. You can shoot some truly fantastic images with nothing more than an EOS camera on a tripod.

At the most basic level is the simple point and shoot approach. Here, in addition to the main subject, it is the composition that will differentiate a great astro image from a mediocre shot. If you are using a camera with a lens of around 50mm, even an object as large and as relatively near as the moon will only occupy a very small portion of the frame. Placing a distinctive subject, such as a tree, in the foreground will add interest.

 

After the simple point-and-shoot approach, photographing star trails requires more patience and a little more astronomical skill. Star trails form interesting arcs around the star Polaris. The closer you are to the horizon, the longer the streaks appear due to the motion being more pronounced the further away from the pole you get.

It is best to shoot star trails away from strong light pollution (typically found in busy cities or towns) as light from street lamps will swamp out the light from the stars during the 3 to 4 minute exposure. However, you can get some great results using a technique that requires little or no specialist equipment.

Above Circumpolar star trails over Castle Mountain in Banff, Alberta. Full moon light provided the foreground illumination. 160 images were taken over a two-hour period and then ‘stacked’ into a single image. EOS 7D with a 15mm lens, 25 seconds at f4, ISO 640. © Alan Dyer

Both point-and-shoot images and star trail images require nothing more than a good tripod and your existing camera. If you want to progress to taking images of galaxies and nebula you will need to invest in telescopes and mounting systems.

If you think of a telescope as nothing more than a very big lens, which can cost anything from a few tens of pounds up to a few tens of thousands, then you’re halfway to bridging the gap between traditional photography and astro imaging.

Telescopes

The choice of telescopes is as complex as the choice of camera lenses. There are essentially three different types to choose from:refractor scope – which is just like a really big lens; Newtonian telescope – which has a larger aperture than refractor scopes and a mirror system; Compound telescope – which combine mirrors and corrective front lenses to offer a long focal length.

Manual focus

When using your camera and lenses with a telescope you will lose any autofocus capability. For astro imaging you need to focus manually unless you invest in quite expensive hardware/software integrated solutions, which will robotically adjust the telescope focus based upon the width of a star point.

As you are usually focusing at infinity, it’s a matter of using your best judgment to focus on a bright star or the moon to get a handle on the focus position.

If your camera has Live View, this is a good opportunity to use it as the 10x zoom function will help you to focus accurately in the dark conditions.

Dedicated cameras

As of 2019, Canon has made three dedicated EOS cameras for astrophotography – the EOS 20Da (2005), EOS 60Da (2012) and EOS Ra (2019). In each of these cameras, modifications have been made to increase the hydrogen-alpha sensitivity of the sensor so that the camera could better record reddish diffuse nebulae and solar flares This is achieved by alterations to the infrared low pass filter, resulting in a 2.5x increase in sensitivity in the EOS 20Da, rising to 4x improvement with the EOS Ra, Canon's first full frame astrophotography model.

Capturing nebulae

Derived from the Latin word for 'cloud', a nebula is typically made up of dust, hydrogen, helium gas and plasma. The colours only show up in long exposure images and the modified infrared blocking filters in Canon's astronomical cameras help to let more of the red light through. From a dark site the outline of a nebula can be made out using binoculars.

Further reading