Photography News issue 25

Technique 32

Photography News Issue 25 absolutephoto.com

equipment suppliers like Orion (SkyGlow and UltraBlock filters), Astronomik (CLS filter), Lumicon (Deep-Sky filter), and IDAS (P2 Light Pollution Suppression Filter), the latter costing about £250 for a 72mmversion. Nothing really beats a dark-sky site however, as found in uninhabited areas, so you may need to travel for the best results, but your efforts will pay off through improved image quality and reduced exposure times or the ability to work at smaller apertures and lower ISO settings. You’ll also need to guard against light pollution caused by yourself. For instance, once your eyes have accustomed to the dark, it’s easy to blind yourself with a regular torch, so invest in a red- beamversionwhenworking in the dark. Taking it further The possibilities of shooting astronomical objects increase when using a camera that’s attached to a telescope, so how do you go about doing that? Well it’s actually quite simple, and while the subject of setting up a telescope itself isn’t something we’ve space to go into here (there’s plenty of great information on the subject in Chris’s book – see panel), the benefits of a telescope’s magnification will very quickly become obvious as, depending on the model, it’ll take you way beyond what’s offered by a telephoto lens. Unlike the photography industry, says Chris, “where we put up with the myriad camera Raw file formats, battery shapes and continual updating of software to keep pace withnewdevelopments, the folkswho designed telescopes and their software collaborated on some standards. One of those standards is the T-thread coupling. Virtually every telescope can be converted to have a T-thread on its end and with the help of a suitable bayonet to T-thread adapter to put on your camera, this allows direct connection.” A quick Internet search will show you that adapters exist for any mount, and they’re not expensive, often costing under £10. “I have adapters for Micro Four Thirds, Fuji X and Canon EOS, says Chris “I used my Fuji X-T1 to shoot colour pictures of the lunar eclipse last month, through a 916mm f/7 refractor.” After focusing the telescope itself, youneed to do the same on the attached camera, and this is best done inmanual focusmode,whileusing the screen as a guide. Zoom in to check sharpness before you get too far into the process. If you’re able to tether your camera to a laptop or tablet, even better as you’ll get a larger view allowing you to achieve critical focus (and possibly be able to sit indoors while you shoot). Tethered shooting also allows remote firing of the shutter, but even if you’re not tethered, a remote release is vital in not jogging the camera and tripod during the exposure. Finishing touches Finally, there’s plenty you can do to improve shots in processing. “Image acquisition is only half of the fun,” beams Chris, and a big part of astrophotography is to do with stacking separate night-sky exposures in software, which, when properly blended, allow you to Nothing really beats a dark-sky site however, as found in uninhabited areas, so you may need to travel for the best results, but your efforts will pay off...

Above Chris’s latest image of Andromeda, taken three years after the first (left). This is the product of about 20-hours exposure time across 100s of different images. Left Chris’s very first image of the huge Andromeda Galaxy – taken with Canon EOS 40D, fitted with a 300mm f/4 L lens.

Learnmore

You can read more on the subject of astrophotography in Chris’s book The Astrophotography Manual , (£31.99) which takes astrophotographers with a basic knowledge onto greater things. The book covers choosing and using dedicated astro equipment and software in a technical yet down-to-earth manner, helping you create the very best quality images since, as things become more sophisticated, the practical and technical challenges multiply too. For more info visit focalpress.com.

create brighter pictures, freer of noise. “Great images are the outcome of patience more than luck. Mine typically comprise about 150-200 separate exposures of between five and 20 minutes each and the same again for sensor calibration. It sometimes takes months to find enoughclearnights tobuildupall the exposures for a single image! Separate exposures are carefully combined, aligned and then averaged, in a way that makes airplane trails, cosmic ray hits andmeteors simply disappear.” Fortunately, many objects in the sky can be captured over an extended period because they simply don’t change, being so far from us that the perspective remains the same. Planets, though, will move, just like the moon. Of course you can do it with fewer exposures, and still feel the benefit, as according to Chris, “every time one doubles the exposure time, or doubles the number of averaged exposures, the relative noise level reduces by 40%.”

Although many people do use Photoshop for image processing, there are packages more specifically engineered to astrophotography processing which you should consider, such as DeepSkyStacker (deepskystacker.free.fr) and Registax (www.astronomie.be/registax), both of which are free. Photoshop, says Chris, “is not the best tool for the job (rather like a Swiss Army knife, it does a lot of things but a dedicated tool is better). Editing programs that are purpose-built for astrophotography deserve a little perseverance to get the very best from your endeavours. The very best quality images use 32- or even 64-bit depth files to preserve the finest graduations during image processing.” And, says Chris, while the outcome of these stacks is still a mostly dark image with a few stars visible, it’s when you start brightening the picture using curves that “the faint details emerge from the gloomand really lift your spirits.”