Discover the Secrets of Astrophotography

Tuesday 18th September 2012

For our monthly lecture we were pleased to welcome Philip Perkins who is an experienced astrophotographer. In his talk "Imaging the Cosmos" he showcased some of the images that appear on his website (www.astrocruise.com) and gave us the benefit of his many years of experience in his efforts to capture the natural wonder that is the night sky.

He began by explaining that he became interested in astronomy from an early age but it was not until 1988 that it developed into something of a more serious hobby. Nowadays he takes most of his images from the south of France and his telescope and equipment travel with him about four times a year from his home in Wiltshire.

He mentioned that he is often asked what drives his passion for astrophotography and replies that it makes the invisible visible and it is an exploration of our greater natural world. He added that the whole process of capturing an image and then processing it to bring out its inherent beauty gives him great pleasure.

He then went on to say that a typical DSLR can take very good astrophotographs. However, some models are better than others as they usually have a built-in infrared filter which does block some of the light from astronomical objects. Good subjects for such a camera would be the planets, the Moon, planetary alignments, lunar eclipses, aurorae, cometary trails or just simply wide-angle shots of the constellations. These are all inherently bright objects and so only need the camera to be on a tripod or solid base using relatively short exposures.

However, to produce pictures of fainter objects means longer exposure times and with a fixed camera the stars would soon begin to leave trails due the Earth's rotation. So, the next step for any budding astrophotographer is to invest in some sort of mounting that can compensate for the Earth spinning on its axis.

For those who do not own a telescope and are practically inclined there are designs on the web for making a "barn door mount". This is a small wooden structure that sits on a tripod and when attached to the camera allows it to follow the arc of the stars as they sweep across the night sky. It usually has a manual device that the photographer has to turn at a certain rate to match the apparent motion of the sky. Of course if you can afford it you can just buy an autoguider that does the tracking for you.

For those with a telescope a computer-driven equatorial mount is needed to follow the drifting night sky. In this case pictures can be taken either through the telescope itself or with a camera bolted on to it or even using a computer webcam in the telescope's eyepiece. Philip strongly recommends spending just as much on a mount as on the telescope and pointed out that an astrophotographer may upgrade their telescope repeatedly but will only invest in a quality mount once in their lifetime.

This article was written for the club news column of the Stratford Herald. The actual lecture explained the subject at a deeper level.