Limerick Astronomy Club: Snaps that are out of this world

by Frank Ryan (Chairman Limerick Astronomy Club)

In the last few years there has been an explosion in the popularity of Astrophotography. Caused by digital SLR cameras and telescopes, generally becoming cheaper to own. Where once you only had a roll of film and had to wait to have it developed; you can now shoot hundreds of images a night at zero cost.

While modern cameras have amazing automatic features, these are more of a hinderance when it comes to shooting the nights sky. For that reason, it’s good practice to know how to use your camera in ‘Manual’ mode. A basic understanding of Shutter Speed, f Stop, ISO and lenses will certainly help. Astrophotography has many areas: One of the easiest to do that will give you great results is Wide Field long exposure.

The trick to getting a good result is a dark sky. Even suburban skies, that may seem dark to your eye will overexpose the image. In fact, almost any nearby bright light in the direction you are shooting will spell disaster. So, Let’s assume you have a dark sky, a tripod and a digital camera, what then? Well you’ll need to point it at something interesting. At this time of year, the constellation of Orion is well positioned in the South at around 9PM. ‘The Hunter’ is a good subject for a few reasons. Firstly, it contains some of the brightest stars in the sky. It also has the ‘Great Orion Nebula’ just beneath the 3 belt stars and best of all, The Milky Way runs diagonally down it’s left side. What’s not to like?

To capture a usable image, you’ll need to set your camera to manual (‘M’). The ‘Shutter Speed’ or exposure time set to 30 seconds. ISO (the sensitivity to light) should be as high as it can go. Turn auto focus off and manually focus as best you can on a bright star or distant light. You can zoom in to a star to focus by don’t forget to zoom back out or else you will get star-trailing.

Once your happy your subject in in frame use a shutter release cable if you have one to take the shot. If you don’t set the timer to take one. The reason for this is you don’t what to shake the camera while clicking the button, although for wide field long exposures this won’t be too much of a problem. Once your shot is taken, have a look at the result on the screen and make sure you are in focus.

Limerick Astronomy Club email limerickastronomyclub @gmail.com