Photography News issue 25

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Photography News Issue 25 absolutephoto.com

Technique

ASTRONOMICALLYGOOD PICTURES

For an extra dollop of inspiration in your night-sky photography, the winners of 2015’s Astronomy Photographer of the Year were recently announced. Included in this year’s winners was David Tolliday’s shot of a stellar nursery that is in the Orion Nebula lying 1300 light years away and the Running Man nebula another 200 light years away, captured from the Elan Valley in Wales. It was David’s first attempt at astrophotography and earnt him the Sir Patrick Moore prize for Best Newcomer. All the winning and shortlisted images can be seen in exhibition at the Royal Observatory Greenwich now, so for more info and to see how you can enter next year’s competition, head over to rmg.co.uk/astrophoto.

Above This is a shot of the recent lunar eclipse, taken half way through with a Fujifilm X-T1 fitted to a 916mm focal length telescope. Here, two exposures were combined to show the light and dark sides without losing detail to the highlights or shadows; one taken at 1/1000sec, the other at 1/4sec. Because the moon is so bright, you can also easily shoot it with a telephoto lens and teleconverter.

muchmovement, and this is a good introduction if you’re not using a tracker. Tracking your quarry Physically tracking the movement of the stars with your camera is something you’ll need to do if you’re using the very long exposures vital for picking up faint objects. Thismeans the stars will stay in the same position on the sensor and won’t blur, as the twomove inunison. “The stars wheel around Polaris (the Pole or North Star) at the rate of 1° every four minutes”, explains Chris “and that’s a moon-width every two minutes.” You can also visualise that distance by holding up your little finger at arm’s length – the width is about 1° of the sky. Of course, objects further from Polaris, will appear to move faster than those closer to it, just like the centre of a wheel moves less than the rim. Unfortunately, tracking the stars isn’t something you can do by hand, like a panning shot. Astrophotographers use motorised equatorial mounts to do it, but these can be anything from DIY barn door models to affordable off-the-shelf versions, while there are also more complicated models that use a second tiny camera to feed back guiding corrections. This, according to Chris, “ensures the imaging camera follows the star to within fractions of a pixel, over the entire exposure. It sounds complicated, but folks all around the world are doing it every night, with all manner of ingenuity and patience.” The right atmosphere The objects you’re trying to image can also be disruptedbyatmosphericconditionsandbylight pollution. Although by no means the only time you can shoot, cold, clear nights, such as those Physically tracking the movement of the stars with your camera is something you’ll need to do if you’re using very long exposures

found in autumn and winter are a great time to do it, as the lower temperatures cut out any heat haze that can blur the subject. Subjects that are higher in the sky, ie. further from the horizon, can also be clearer because you’re viewing them through less of the Earth’s atmosphere; when you see a star twinkling that interference caused bymoving pockets of air, so the less air the better (that’s why the best telescopes are in space). “Autumn is a favourite time for me,” says Chris “but each season brings its unique rewards and even in the height of summer, it is possible to image the moon, bright clusters and star-fields.” And despite what youmight think, “some of the best imaging conditions are immediately after a shower,whereas anti-cyclones [as found inhigh- pressure, fine weather], often cause high-level mist and dust to accumulate in the atmosphere, whichmakes observation poorer.” The spill of light from our over-illuminated towns and cities also means that observing and recording the night sky becomes more difficult, but, says Chris, you shouldn’t let an urban location put you off from having a go: “Light pollution appears like a nicotine haze, but it’s possible to reduce its effects during editing. Better still, is to use a filter which selectively blocks the commoncolours fromstreet lighting.” Generically, these are called broadband light- pollution filters and they’re made by astronomy Above This image of Jupiter is the result of Chris’s first attempt using awebcam mounted onto a longish telescope and also fittedwith a teleconverter. He shot a 90 second video then used Registax software to align and process the 1000s frames into a final image.

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