Starlight Exposure

I’ve always loved starlight photography but haven’t had that much opportunity to play with it- usually a combination of always having poor camera gear when I’ve been among great starscapes, versus living in the suburbs with my high-quality gear. Marrying my good camera equipment with a nice clear starry night has proven to be a challenge.

I got a couple of good nights however recently down on Victoria’s Great Ocean Road, where the Split Point lighthouse at Airey’s Inlet sat beneath the spectacular Milky Way on a couple of moonless nights.

There are a couple of approaches you can take to starlight photography. Stars move- quite quickly in fact. Well, they move in all sorts of directions, some of them at ridiculously high velocities, and on average, away from us here on earth. However they are so infintessimally small in our night sky, and the distances so huge, that we certainly won’t be able to record this without scientific aid. However, because the earth is spinning in space, relative to use the stars appear to move through the night sky, spinning about a notional pole which is directly above our axis of rotation at the north and south poles.

But relative to us, the motion of stars can be seen in as little as ten or fifteen seconds on a long-exposure photograph. The effect, as many of you will have seen (and which I’ve put up a couple of here and here) is an apparent streaking of the stars in a radial motion- quite dizzying in fact. Leaving a shutter open for ten minutes or so can produce this motion, although with the right equipment and conditions you can leave a shutter open for far longer- even hours.

Taking a long-exposure shot of this kind requires (as a minimum) a tripod and a remote shutter-release mechanism (to avoid your fingers making the camera shake when you click to start the photo running). Windy nights aren’t much fun as they will make the camera shake unless you have a rock-solid tripod and leave you with some blurriness. The effect works best when there’s a static object in the frame as a contrast, giving an otherworldly image that is very eye-catching. In doing so, however, you have to also think about how the exposure will balance on this other object as well as the stars- in effect, balancing for two different light sources of differing intensity. Moonlight nights, for example, will rapidly overcome the sensor and leave you with a white image. Well balanced, the effect can be spectacular as the moon (reflecting the same light as the sun but at a lower intensity) gives the scene the same colour-pallete as broad daylight, but with a trail of stars left in the sky instead.

In the shot above I’ve not done anything particularly clever, just left the shutter open for a while at a slightly lower aperture and sensitivity so as not to overexpose the lamplight from the lighthouse beacon. I esimated this taking a short frame at maximum sensitivity, getting the right exposure, then reducing the exposure arithmetically and increasing the shutter speed by the corresponding factor (translation: If I get good exposure with ISO 1600 for 1 minute, I will get the same exposure with ISO 100 for 16 minutes) (note: this last is not entirely true as by reducing the sensitivity, because the stars are moving they may not imprint as brightly on the sensor so their trails may be dimmer).

Another option (demonstrated in this second shot) is to try and capture the stars themselves as pinpricks. This is far more difficult as you realistically need both an incredibly clear and light-pollution-free night (away from city lights, artificial lights and moonlight), and a pretty high-quality camera and lens. Clarity is essential- desert skies- notorious for beautiful starscapes- are often difficult to shoot in due to haze, for example. In the case of this next photograph, I am using my Canon EOS 5D (a very good quality piece of kit) at maximum sensitivity (at ISO 1600 the shots can be a little noisy but are still usable much of the time), and my Canon EF 16-35mm f/2.8 L USM lens. Translated, the lens is massively wide- a vast field of glass that sucks light out of places you wouldn’t expect to find any. To the naked eye, the night was not nearly as bright or star-filled as the camera was able to pick up, which I find quite amazing, and which is one of the reasons why this lens is one of my absolute favourites. I actually discovered this trait of the lens almost by accident taking some ‘short’ long-exposures in Western Australia last year, expecting to find only a few points of starlight and instead finding the whole Milky Way on my sensor. It was an exciting moment. The combination of sensitive sensor and massively light-accomodating lens means that by exposing for just a few seconds (15-30) I can ‘freeze’ the moving stars behind my main subject before they deteriorate into star-trails, giving a totally different effect (and one which I have decided I quite prefer). Even a 20-second exposure has some blurring of the stars- they move that quickly- but at screen resolution this motion is hard to pick out.

Starlight photography remains something I enjoy, although something which I need to practice a little more and which I am looking forward to increasingly adding to my portfolio. I hope you’ve enjoyed it thus far as well.

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