5 Reach for the skies

Serious star shots need serious kit for out-of-this world results

Winter means cold clear night skies, so it’s the perfect time to discover the joys of astro-photography. Rather than just taking shots of the moon, however, we are talking about the real deal – gloriously detailed images of distant galaxies, as taken by keen amateur photographer, Dave Watson.

Dave uses a refracting telescope that is specifically designed for astro-photography. We’re talking some impressive numbers. “The telescope has a focal length of 450mm at f/5.3, but using a reducer I have the option of a focal length of 328mm at f/3.8, which gives me a maximum field of view of 3.0 degrees x 2.4 degrees x 2.4 degrees of the sky,” he explains. Dave uses a monochrome astronomical camera capable of 16-bit resolution, and is easily controlled by a computer.

To combat noise, caused by the lack of light in the night sky, Dave takes ‘dark calibration’ images. “These are images taken at the same exposure and sensor temperature as the object image, but with the lens cap on. This records only the random noise. I take 35 of these images and combine them into a single image for later processing.”

To further reduce visual noise while boosting the signal strength, Dave has to take many images of a heavenly body before blending them together. “You simply cannot have too much data,” he explains.

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* An apochromatic (APO) refracting telescope is recommended, with a focal length of 450-600mm at f/5.6. Dave also recommends a 450mm f/5 telescope for autoguiding. * Dave recommends a good-quality German equatorial mount for stability and accurate tracking. It needs to be computer controlled. Hardware to keep the telescopes rigid is also needed, as well as a heavy-duty tripod * The ‘autoguider’ camera can be a cheap, 8-bit monochrome device with a 1,280 x 1,024 sensor, while your main SLR will work as the main imaging camera – although you will need to buy the appropriate adaptors to fit the camera to your telescope.