Dazzling deep skies
G
etting amazing images of objects in deep space isn’t down to magnification or effective focal length: in fact, there are some very good reasons to start out at lower magnifications. It’s easier to get sharp results with lower-power telescopes, and they also usually let in more light than high-powered models. The important elements in successful shots are the quality of the telescope, the smoothness of the tracking mount and accurate alignment. Here’s more on the four key areas you need to consider… figures: these refer to the magnification for viewing with an eyepiece fitted, so you can ignore the figures for photographic purposes. To find out how a telescope will work with your camera you’ll have to dig a little deeper into the specifications and find the focal length. Sometimes this is expressed as a number such as f/500, which looks like an aperture, but is actually the focal length – just the same as the focal length as a normal lens.
The most important figure for astro-photography, the effective aperture, isn’t always clearly stated in the specification. But all you need to do is divide the focal length by the diameter of the objective lens. For example, a telescope with an 80mm diameter and a focal length of 600mm will have an aperture of f/10. strengths and weaknesses. If you are just starting out in astro-photography and want to use an SLR with a telescope, the best option is a refractor telescope with ED or apochromatic elements.
You’ll also need a mount to fix your camera to the scope. These vary according to the manufacturer, but most designs replace the eyepiece with a tube assembly, onto which you can screw an adapter called a T2 mount that enables you to attach your camera body.