Photography News Issue 30

Photography News Issue 30 absolutephoto.com

Technique 56

Picking a neutral density filter

Long exposures can happen quite naturally – all you have to do is hang around until your location has spun sufficiently away from the sun. But while patience is a virtue, neutral density (ND) and long exposure (LE) filters give you flexibility, the latter allowing very slow shutter speeds even in broad daylight. ND and LE filters block light from entering the camera, and their strength (how much they reduce the light) is measured in ‘stops’; a stop being a doubling or halving of an exposure value. A one-stop ND cuts the amount of light in half; meaning that a 1sec exposure becomes 2secs. Commonly, NDs come in strengths up to three stops and having a range of them is a good idea as it will allow you to get just the shutter speed you want. For example, although a strongish, three-stop filter might seem a good idea, it can block too much; get a one-, two- and three-stop filter and you can stack them to combine the strengths (though this risks vignette on screw-in versions). All filter companies offer a range of NDs, so there’s lots of choice. You can get screw-on NDs like a Hoya 77mm ND 0.6 (two-stop) filter for just £59 or, if you prefer using slot-in filters and a holder, try Cokin’s P-Series Full ND Kit, which fit DSLRs with APS-C sized sensors and includes three resin filters covering one, two and three stops, plus a holder for only £50. Both need matching to your filter size and the Cokin needs an adapter ring, but that’s only a few pounds. Then there’s LE filters, so called because they make no claims about leaving the colours in the pic neutral and often add a slightly warm or cool cast. There’s the famously brilliant Lee Big Stopper at around £100, which fits into the Lee Filter Holder Foundation Kit (£55). Or try Hoya’s screw-in 77mm Pro ND 1000 at £60. Both offer ten stops of light reduction. Finally there are variable filters which allow a range of light-absorbing strengths to be set; for example, check out Vü Filters 77mm Sion Variable ND which covers one to seven stops, adjusted by turning the bezel.

So, once you’ve decided that your composition needs a long exposure, what speed should you use? As mentioned earlier, this depends on the speed of movement in the scene and the amount of blur that you want to produce. Say for example you’re shooting at the coast and you want the viewer to feel the motion of the tide. That’s likely to need a shutter speedof two to five seconds, depending on the speed of the waves, which will produce pleasing streaks of surf. Use a shorter speed and there will be too much texture; longer and the tide will mist to the point of being invisible, or you may get the water coming in and out, which lacks direction. If, on the other hand you want the water to form a mist, making clear islands out of whatever’s in it – a sea defence, harbour wall or the end of a groyne – you’ll need a lot longer. Empty or still? Long exposures can cause problems with composition as well as adding to a scene; it all comes down to whether the blur makes large areas of a scene look empty or vacant in a bad way – or if that blur adds something to the arrangement you’ve created. Take a river for example: at a relatively normal shutter speed of 1/60sec or 1/125sec, the water will be textured; but slow this to a few seconds and the smoothness produced can make the water into a cleaner, simpler, more obvious lead-in, taking your eye to whatever’s in the distance.

Conversely, open tracts of blurred water can unbalance a picture, so unless the image is meant to convey a feeling of emptiness, it might be better to avoid a long exposure, or reframe so that there’s more ‘going on’. This is why very long exposures where most of the scene is blurred often work with central or symmetrical compositions; emptiness forces the eye onto the subject, and if it’s off centre that can sometimes look awkward. Try to work slower and visualise how the scene might lookwith its motion blur, because you’ll never get those three minutes back (and it’s six minutes with in-camera long-exposure noise reduction). On the subject of which… Noise in the nothing Very long exposures cause a build-up of digital noise in pictures, which is different from the grain produced by using high ISO settings alone; it comes from the sensor heating up during the exposure and leaves speckles (hot pixels) and casts, especially around the edges of the frame. To combat this, cameras have a long-exposure noise reduction feature, which is usually turned on by default when the shutter speed goes over a certain time, like 2secs. In this process, at the end of the exposure, the camera creates another of an identical length without actually opening the shutter. This is then compared to the first exposure, allowing the interference to be filtered out automatically.

The only problem here is that if you’re creating exposures of a few minutes, you’ll be doing a lot of waiting around on top of the shooting time. What’s more modern DSLRs don’t shower the image with noise like older models, so you may not need it at all if you’re only shooting for 30secs to a minute or thereabouts, so seek out the function in the menu and turn it off. Raw power When it comes to finishing off your long exposures in post-processing, the use of Raw format is a big advantage. This means that slightly over or underexposed pictures are easier to tweak during processing in Adobe Photoshop or Lightroom. Using the Exposure, Whites, Highlights, Blacks and Shadows sliders means you fine-tune an picture’s density and contrast while any minor colour shifts in the image can be resolved with the Temp and Tint sliders. But the advantages don’t end there. Using the HSL/Grayscale tabs let you apply a simple monochrome finish, which always suits the other-worldly look of long exposures. And if you want a subtle wash of colour, there’s the Split Toning tab right next to it. To create uniformity in your long exposures, you can also try toning them all the same way and also using the same Crop tool settings, applying either a square or a 5:4 crop, so that a harmonious series is created.