Photography News issue 25

Photography News Issue 25 absolutephoto.com

Technique

Shooting themoon with a telephoto zoom

Shooting the moon is how most of us cut our teeth in astrophotography, and quickly find out that it’s not as easy as first thought (though a good deal easier than shooting smaller, dimmer objects). But in a few simple steps you can get excellent lunar images. As Chris says: “a sturdy tripod and a telephoto lens with a teleconverter will deliver good results. The trick is to take a few dozen images and ruthlessly discard those blurred by atmospheric turbulence”. You can even shoot it in the daytime or low-light for a different look.

First though you’ll need a lens with a long focal length, because although the moon can look large to the naked eye, it’s actually pretty small – about the width of your little finger when held at arm’s length. Shoot it at the long end of your 18-55mm and it’ll still be tiny in the frame, but a lens like the Tamron 150-

600mm, at around £800, will get you nice and close. You can also increase focal length with a teleconverter (see this month’s Buyers’ guide), or simply shoot with something like a 70-300mm lens and crop the pic in Photoshop. If you’re handholding, switch any image stabilisation on to avoid camera shake. Exposure is the next hurdle; the moon is actually surprisingly bright (it’s a very efficient reflector), and, as it won’t fill much of your viewfinder, multi-zone metering will average out the scene and turn the moon into a glaring, featureless beacon. Therefore you need to switch to manual mode. Of course, the actual brightness depends on the phase of the moon (how much of it is out of the Earth’s shadow and reflecting the sun), but kick off with something like 1/200sec at f/5.6, ISO 200. The moon is also surprisingly fast – when zoomed right in, it’ll appear to sprint across a locked-off frame, so you’ll need to recompose often. Once you’re comfortable with the basics, shoot the moon in different phases – at its half and crescent stages it’s often much more interesting than full, because like terrestrial landscapes, when the sun strikes the moon at a more oblique angle, the detail of its surface is more prominent.

Above Another subject in the night sky that many take using a DSLR and a telephoto lens, Chris’s image of the Horsehead nebula was shot “with a short focal length telescope and a lot of patience.” Due to very different light levels, the nebula and stars were captured in different exposures and combined later on.

Above This image of the Heart nebula is an example of something you can move onto as your astro skills grow. Chris employed a narrowband imaging technique, using filters to pick out the ionised oxygen, sulfur and hydrogen gases in the nebula – a bit like using an IR filter to shoot just that part of the spectrum.

Not so happy trails When it comes to shutter speed, you’ll need exposures of many seconds or oftenminutes for the fainter objects, and this is where tracking comes into play. When shooting from a regular tripod in a locked-off position, you’ll pick up unwanted movement in the stars’ paths; the longer the focal length of the lens you’re using, and therefore the more cropped your view of the sky, the more exaggerated this will be as the movement of the Earth is picked up, turning the stars into streaks of light. In fact, movement is one of the biggest challenges in astrophotography – movement combined with the lengths of exposure needed to pick the dimmer and more interesting objects in the night sky. But as Chris says, “the technical challenges really only start when you try to increase the image magnification and the length of the exposure to capture small and dark objects. That’s when you need a mount to track starmovement.” That means, of course, that you can shoot shorter exposures atwider focal lengths and still enjoy the night sky, as youwon’t be pickingup so

Aside from the technical challenges of shooting the night sky and the pleasure of overcoming them, astrophotography can also offer up more aesthetic struggles, because, as Chris elaborates, “you can often tell if an astrophotographer is already a photographer, just from their images. Rather like the early days of digital photography, some beginners get carried away with the effects and lose sight of finesse! A good image has colourful, small and round stars, as well as subtle detail in the galaxy or nebula, without any obvious digital noise.” One small step So how do you get started? Well, for detailed shots of the night sky, all you really need is a telephoto lens (possibly with a teleconverter attached), a sturdy tripod and a means of tracking the stars’ movement through the sky; used in the right way, these will be enough to get good astro photos and if you enjoy what you’re doing and want to get more magnification, you can take it further by investing in more specialised kit. What that means is that you’ve probably got most of the kit you need already.

light. Therefore, switch to manual mode and dial in a wide aperture to let lots of light in. Telescopes are designed to only operate at full aperture (about f/5.6 to f/10) but with a camera lens you might want to stop down to improve optical quality across the entire image. As Chris says, “although stars are a simple subject, they are the most demanding subject to photograph, so much so that star images are used for testing optics”. Because many of the more interesting astronomical objects are very dim and faint, be prepared to use high ISO sensitivities, too. This will introduce more digital noise into your shots, but that’s a small price to pay for more detail and with the right software you can filter it out. Focusing can also be tricky in the dark, so it can be a good idea to focus on a distant object in daylight, then leave the lens set there and switch to manual so it doesn’t wander when you come to start shooting. Alternatively, if your lens has a focus distance window, manually set it to infinity, but check the results on screen to make sure you’re getting the stars pin-sharp – and don’t turn the focus ring past the infinity marker, whichmost rings will do.

“There’s often amisconception” says Chris, “that youneeda long telescope; butmost ofmy images are taken with lenses of 400mm focal length or shorter.” Indeed, with the right settings andwith the right weather and atmospheric conditions you can shoot objects you’d think were taken using much more sophisticated gear. “The Andromeda Galaxy is a favourite, also given the catalog name M31,” enthuses Chris “It is BIG, about6xwiderthanthemoonatitsfullestextent, and relatively bright. My first photographs used an APS-C DSLR, fitted with a 300mm lens and a 1.4x teleconverter. That’s all youneed to deliver your first ‘wow’ moment.” But before you head out, remember that shooting at night can get chilly even in the summermonths,sowrapupagainstthecoldand also give your camera and lens time to adjust to the change in temperature; putting them in your bag and standing it in a cool spot for an hour or so before venturing out is a good idea. Get sensitive Before we come to tracking, the camera still needs to be set up so that it’s very sensitive to