Lens Filters – Choosing the Right One for the Right Image
Of all the digital camera accessories lens filers are one of the best tools in a photographers camera bag. Lens filters and camera hoods should be an important part of any photographer’s camera bag whether professional or amateur. Lens filters can include polarising filters that reduce glare and improve the saturation of the shot, or simple UV/haze filters that provide extra protection for your lens. These days, the most common filters used within digital photography include polarising filters (linear/circular), UV/haze filters, neutral density filters, graduated neutral density filters and warming/cooling or colour filters.
Here are is a quick insight into the lens filters. I will go into more detail about each lens filter later in the piece.
Linear/circular polarising filters help to reduce glare and they improve the saturation of the image. They are generally used when taking pictures of the sky, water or foliage and also used to get great results in landscape photos.
A neutral density (ND), are used to extend the exposure time. These are generally good when used while taking pictures of waterfalls or rivers (moving water) under bright light. Another type of neutral density filter is a graduated neutral density (GND) filter. These filters help to reduce vignetting and help control strong light gradients. Using GND filters while photographing dramatically lit landscapes can create spectacular results.
There are also UV/Haze filters that improve the clarity with film. They also provide lens protection and can be used when taking any sort of picture. For the more advanced photographer there are warming/cooling filters. These change the white balance of an image and are best used when photographing underwater or when there is some form of special lighting.
Polarising filters
Polarising filters are perhaps the most important filter for landscape photography. This is because they work by reducing the amount of reflected light that passes in to your camera’s sensor. Working in a way similar to a pair of polarising sunglasses, polarisers will make skies appear deeper blue, they will help to reduce glare and reflections from water and other surfaces and polarisers will reduce the contrast between land and sky. If you are using a polariser you can use your camera’s viewfinder (or rear LCD screen) to sample the effect as you rotate the polarizing filter to find the right setting for that perfect image.
The polarising effect can also be increased or decreased depending on the direction that your camera is pointed and the position of the sun in the sky. The polarising effect is strongest when the camera is pointed in a direction that is perpendicular to that of the sun’s incoming light. So, if the sun is directly overhead, the polarising effect should be greatest near the horizon in all directions. Polarising filters should however be used cautiously because they may affect the photo adversely. Polarisers dramatically reduce the amount of light reaching the camera’s sensor. This means that the risk of a blurred image goes up dramatically whilst the camera is hand held. This may make some action shots prohibitive although this may be combatted by using a tripod.
Linear vs. Circular Polarising Filters
The circular polarising filter is designed so that the camera’s metering and autofocus systems can still be used. Linear polarisers are much less expensive, although, they cannot be used with cameras that have through-the-lens (TTL) metering or autofocus (nearly all digital SLR cameras).
Neutral density (ND) filters
ND filters are used to reduce the amount of light reaching the camera’s sensor. This may be useful when a sufficiently long exposure time is not otherwise attainable within a given range of possible apertures. Situations where using ND filters could be particularly useful include: smoothing water movement in waterfalls, rivers, oceans, etc. The ND filters allow a shallower depth of field in very bright light. You should only want to use ND filters when it is absolutely necessary as they effectively discard light. In addition to this effect, some ND filters can add a very slight colour cast to the image.
Graduated Neutral Density (GND) filters
GND filters restrict the amount of light that is across an image within a smooth geometric pattern. These lens filters are sometimes called “split filters”. Images that are ideally suited for GND filters are images with simple lighting geometries. These are images such as the linear blend from dark to light encountered commonly in landscape photography.
GND filters come in many varieties. The first setting is how quickly the filter blends from light to dark. This is usually termed “soft edge” or “hard edge” for gradual and more abrupt blends, respectively. The type of filter that is chosen is based on how quickly the light changes across the image. For example, a sharp division between dark land and bright sky would necessitate a harder edge GND filter.
Placing the blend should be performed very carefully and usually requires the use of a tripod. The softer edge is generally more flexible and forgiving if misplaced. On the other hand, a soft edge may produce excessive darkening/brightening where the blend occurs, this may happen if the scene’s light transitions faster than the filter. Another thing to take into account when using GND filters is being aware that when using the filters vertical objects extending across the blend may appear unrealistically dark.
The second setting is the difference between the amounts of light that is let in at one side of the blend compared to the other.
Haze and UV Filters
UV filters are primarily used to protect the front element of a camera lens since they are clear and do not noticeably affect the image. When using film cameras, UV filters aid in reducing haze and help to improve contrast by minimizing the amount of UV light that reaches the film. UV light is not visible to the human eye, but is often uniformly distributed on a hazy day. UV light therefore adversely affects the exposure by reducing contrast. Most digital camera sensors are nowhere near as sensitive to UV light as film, therefore UV filtration is no longer needed.
UV filters do have the potential to decrease image quality. This may be caused by increasing lens flare, adding a slight colour tint or reducing contrast.
Cooling or Warming filters
Cooling or warming filters help to change the white balance of light reaching the camera’s sensor. These filters can be used to either correct an unrealistic colour cast, or to add one, such as adding warmth to a cloudy day.
These types of filters have become less important with digital cameras since most automatically adjust for white balance. This can also be adjusted afterwards when taking photos with the RAW file format. Some situations may still warrant the need for colour filters, such as situations with unusual lighting or underwater photography.
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