Lens filters are some of the most useful photographic accessories, yet their importance is often overlooked in the world of digital photography. With so much post-production and retouching software available to us, it is easy to adopt the mentality of ‘fixing it later in Photoshop.’ But lens filters are a valuable tool that every photographer should try using at least once.
Lens filters are small circular pieces of glass or plastic that screw onto the end of a lens. There are many different types of filters, all with their own characteristics and purposes. Some are used for protection, some for altering colour, and others for darkening particular areas of an image. Let’s have a look at some common filters, and find out what they are used for.
A UV filter is often the first type of filter that new photographers encounter. It is essentially a clear piece of coated glass, and is mostly used for lens protection. The name of this filter comes from its original purpose, which was to block ultraviolet (UV) light. Early photographic film was very sensitive to this type of light. It caused undesirable effects, such as haziness in black and white film, and a blue tinge in colour film. As a result, using UV filters was standard practice.
However, digital cameras and modern film are not sensitive to UV light, so this type of filter is now most commonly used as a protective device. Because the filter is clear, it does not affect the exposure of images, and so is a perfect shield from dust and scratches. It’s much more affordable to crack a $30 filter than a $3,000 lens!
Although UV filters are the cheapest types of filters, it is important to invest in a quality one. A good UV filter will protect your lens without affecting your images; poor quality UV filters could introduce lens flare and alter the contrast in your shots, making them look washed out.
A polarising filter is also sometimes referred to as a ‘polariser.’ This type of filter reduces the amount of reflected light entering your camera, and is commonly used for landscape photography. Most noticeably, polarisers reduce glare, and help to lessen the intensity of reflections from water and other shiny surfaces (glass, sweaty skin, etc.)
The sun through the trees has been captured in this image without washing out the entire scene, because the light is passing through the filter first instead of hitting the lens directly.
Polarising filters are special because they can be rotated to allow or block polarised light through the lens. Allowing polarised light to pass will enhance reflections, and blocking it will diminish them. For example, say we are photographing a house from the outside, looking in, and the house has large glass windows. Rotating the filter to allow polarised light to pass will cause our image to show reflections of the outdoors in the windows. But rotating the filter the other way, to block polarised light, will block those reflections, allowing us to see into the house.
The same goes with taking a photograph of a water surface such as a pond. With no filter, we would see the sky reflected in the water but using a polarising filter will remove this reflection, and allow us to see under the water.
Neutral Density Filter
Neutral density filters (commonly referred to as ‘ND filters’) are like sunglasses for your lenses. They evenly reduce the amount of light entering the lens, thus resulting in a darker image. In doing so, ND filters allow us to use a combination of ISO, aperture, and shutter speed that would usually result in an overexposed image.
ND filters are graded according to their optical density, or the equivalent number of f.stops they reduce. For example, a 2-stop ND filter will reduce the same amount of light as closing the aperture by 2 stops.
Say we wanted to capture this waterfall with a slow shutter speed, to blur the movement of the water and make it appear milky and smooth. We would probably need to use a very slow shutter speed – leaving the shutter open for a couple of seconds (such as 1/3) at least! But doing so will cause too much light to enter the camera, and our image would look far too bright. In this instance, we can use an ND filter to block light, thus darkening the overall image, and allowing us to use the desired slow shutter speed.
ND filters are also very handy when taking photographs in strong sun with wide-open apertures. Let’s say you have to have to shoot in the midday sun, but you also want to use a wide-open aperture to create a shallow depth of field. Using a wide aperture will let a lot of light into the camera, but by using the ND filter the photo won't be overexposed (although you'll have to watch how your shadows and highlights are falling on your subject even when using a filter).
Graduated Neutral Density Filters
A graduated neutral density filter works in the same way as a regular neutral density filter, except that the light being blocked from entering the lens is not uniform. Whilst a regular ND filter blocks light evenly across the whole image, a graduated ND filter only blocks light from part of the image (usually the top.) This is useful for images which are bright in only one area — such as an open sky.
There are two main types of graduated ND filters; hard edge, and soft edge. The hard edge kind has a strong division between the part which blocks light, and the part allowing light to pass. On the other hand, the soft edge kind has a gentle gradient between the blocking and passing areas of the filter. Graduated ND filters are very useful when capturing landscapes, as they can help to balance out the range between highlights and shadows within a scene. If you’ve ever tried to capture a landscape during the day, you may notice that your foreground (grass, hills, and other elements) may be correctly exposed, but your sky is far too bright, or even blown out. Adding a graduated ND filter will retain the same exposure in the foreground but darken the sky off, so your landscape looks more balanced and even.
The highlights in the sunset in this photo are balanced with the lowlights because of the use of a graduated ND filter. Image taken by Greg Mullins.
The purpose of warming and cooling filters is to alter the colour temperature of an image. A warming filter appears orange or amber, and a cooling filter looks blue. These filters can be used to correct colour casts, or to add a particular colour temperature to enhance the mood of the scene. These filters were used a lot during the days of colour film, to get the colours looking correct. However, they are rarely used in digital photography, as we are able to set our white balance in camera, and can alter it easily in post-production, using programs such as Adobe Photoshop or Lightroom.
How To Choose A Filter
Filters come in different sizes, and you will need to select the correct size to fit your lens. The size refers to the diameter of both the filter and the lens. Because the filter screws on to the end of a lens, it is important to get one that fits properly. A filter that is one size too big or too small won’t be able to attach to the lens, so make sure to get the correct size.
Choosing what kind of filter you need is a totally personal choice. Prices for filters can range from $15-$100 depending on the quality so the decision of how much to spend depends on how useful a lens filter will be to your photography. Consider what you like shooting, and how filters could enhance that particular subject.
For example, if you like to capture long exposures, then an ND filter may be for you.
Keen on landscapes? A polarising filter could be beneficial.
Just want to protect your lens in case you drop it? A UV filter would be perfect.
Or choose a filter you would never think of using, and give it a try. On some cameras several types of filters can all be used at the same time. Start with one and experiment. You might find it opens your eyes to a whole new style of photography.