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Filters and Digital Photography

Black-and-white photographers may still use round glass contrast filters, especially if they stick to a small number of lenses (film camera makers often standardised on a single filter size across a number of lenses in the range for this reason). Colour photographers may still use UV or Skylight filters. In the past, these helped cut haze in distant landscapes, but digital sensors seem less prone to this than film, and nowadays most people use them simply as lens protection. It’s a lot cheaper to replace a filter than it is a lens. You can still get colour-correction filters in glass, too. Hoya still makes and distributes round filters, and there’s a wide range available from B&W, a division of Schneider Kreuznach in Germany. They may be less versatile than square filters, but don’t rule them out. These days, though, square filter systems are far more popular. The filters are made of plastic rather than glass, but it’s rare to be able to see any obvious effect on image quality. The sheer versatility of these filter systems is likely to outweigh any theoretical optical compromises you might be making. Square filter systems are based around a filter holder of a fixed size. These are attached to the lens via adaptor rings. All you have to do is simply buy an adaptor ring to fit the lens’s filter thread. If you use more than one lens, you get an additional adaptor ring for each lens. The square filters that slide into the filter holder are a fixed size, too. This ensures complete compatibility across the range. The only thing you need to make sure of is that these filters are large enough to cover the lens and its angle of view without any corner shading or vignetting. This can be an issue with SLR kit zooms at their widest setting, particularly those with large front elements. It’s even more important with superwide zooms, and it may be necessary to test a filter system before you invest.

The main manufacturers of square filter systems are Cokin and Lee. Lee concentrates on the professional end of the market, while Cokin has traditionally been popular among amateurs and enthusiasts. Cokin filter systems come in four sizes: A, P, Z and X. Users of digital SLRs need to check out the P system – the A size is too small for wide-angle lenses. Using a square filter system is straightforward. Filters are slotted into the grooves in the holder and can be used individually or in combination to create different finishes. For example, you might want to control a bright sky in a landscape shot and warm up the colours too – an ND grad and a warmup filter used together will do the job. This also cuts down on the number of filters you need to take with you when shooting. Different skies need different degrees of darkening, but with just two ND grads (2x and 4x), you can do without a third (an 8x) for those rare occasions where a two-stop reduction in sky brightness isn’t enough.

Filters can also be moved up and down in the holder, and in this way it’s possible to place the transition of a graduated filter on the horizon. If the horizon slopes, rotate the filter slightly – though take care here because a sky that darkens at an angle can look plain wrong. Although square filter systems are very versatile, they don’t suit each and every lens. That’s because many cheaper lenses rotate the front element (where the filter thread is) during focusing. This isn’t a problem during normal (unfiltered) photography, but obviously it becomes a problem if you’re using a polariser or a grad, both of which rely on precise rotation to work. One solution is to hold the filter holder with one hand while the camera focuses, but this only works if the filter holder rotates freely and/or if the camera’s AF motors are powerful. The alternative is to focus manually, though this will rotate the front element, so you’ll still have to grip the filter holder during focusing and the focus ring may not be too easy to get to during this process. Those who use filters a great deal should look out for higher-quality lenses since these seldom have rotating front elements.

The other issue with square filters is that they can be tricky to handle and they’re easily damaged. It’s not always easy to get them out of a bag and slide them into the holder without leaving fingerprints on them, and even a slight brush against a greasy or sharp surface can leave them marked. Square filters are best treated as semi-disposable items. With care they may last you many years, but at the same time you should expect to have to replace them periodically if they’re used often. Not every digital photographer will see the need for filters or want to use them, but we hope we’ve demonstrated that many filter types still have a place in digital photography. Some (polarisers and grads) achieve effects you can’t readily duplicate in Photoshop. Some (colour-correction filters) help you achieve consistent, predictable colour and others (effects filters) can achieve in just a few moments what it might take you several minutes to achieve in Photoshop. The point that’s seldom made about filters is that they offer a different way to take photographs. It’s an opportunity to finish the shot in the camera, rather than just delaying the process until later on. They don’t just help you take better pictures, but they can help you visualise them more effectively as well.

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