Photography Filters

Posted by Alan Tunnicliffe

Filter Type	Primary Use	Common Subject Matter
Linear & Circular Polarisers	Reduce Glare Improve Saturation	Sky / Water / Foliage in Landscape Photography
Neutral Density (ND)	Extend Exposure	Time, Waterfalls, Rivers under bright light
Graduated Neutral Density (GND)	Control Strong Light Gradients Reduce Vignetting	Dramatically Lit Landscapes
UV / Haze	Improve Clarity. Provide Lens Protection	Any
Warming / Cooling	Change White Balance	Landscapes, Underwater, Special Lighting

 

Polarising filters are perhaps the most important of any filter for landscape photography. They work by reducing the amount of reflected light that passes to your camera’s sensor. Polarisers will make skies appear deeper blue, will reduce glare and reflections off water and other surfaces and will reduce the contrast between land and sky.

The intensity of the polarising effect can be varied by slowly rotating your polarising filter, although no more than 180° of rotation is needed, beyond this the possible intensities repeat. Use your camera’s viewfinder (or rear LCD screen) to view the effect as you rotate the polarising filter.

The polarising effect may also increase or decrease substantially depending on the direction your camera is pointed and the position of the sun in the sky. The effect is strongest when your camera is aimed in a direction which is perpendicular (at 90 degrees) to the direction of the sun’s incoming light. This means that if the sun is directly overhead, the polarising effect will be greatest near the horizon in all directions. If the sun is directly to your right or directly to your left the polarising effect will be greatest directly in front of you.

Polarising filters should be used with caution because they may adversely affect the photo due to camera shake. Polarisers dramatically reduce the amount of light reaching the camera’s sensor—often by 2-3 f-stops (1/4 to 1/8 the amount of light). This means that there is a greater risk of blurred handheld shots.

Additionally, using a polariser on a wide angle lens can produce an uneven or unrealistic looking sky which visibly darkens. The sky could be considered unusually uneven and too dark at the top.

Linear vs. Circular Polarising Filters: The circular polarising variety is designed so that the camera’s metering and autofocus systems can still function and is almost certainly the filter you should purchase. Linear polarisers are much less expensive, but cannot be used with cameras that have through-the-lens (TTL) metering and autofocus.

Neutral Density filters – (ND) filters uniformly reduce the amount of light reaching the camera’s sensor. This is useful when a sufficiently long exposure time is not otherwise attainable within the available apertures even if you use the lowest ISO setting.

Situations where ND filters are particularly useful include:

• Smoothing water movement in waterfalls, rivers, oceans, etc.
• Achieving a shallower depth of field in very bright light
• Making moving objects less apparent or not visible (such as people or cars)
• Introducing blur to convey motion with moving subjects

Only use ND filters when absolutely necessary to obtain the effect you want. By reducing the light, you will risk more camera shake by using slower shutter speeds.

Understanding how much light a given ND filter blocks can sometimes be difficult. Manufacturers list this in many different forms:

Amount of Light Reduction
f-stops	Fraction	Hoya, B+W and Cokin
1	1/2	ND2, ND2X
2	1/4	ND4, ND4X
3	1/8	ND8, ND8X
4	1/16	ND16, ND16X
5	1/32	ND32, ND32X
6	1/64	ND64, ND64X

Generally no more than a few f-stops are needed for most waterfall scenarios. Extreme light reduction can enable very long exposures even during broad daylight.

Graduated neutral density (GND) filters restrict the amount of light across an image in a smooth geometric pattern. These are sometimes also called “split filters”. Scenes which are ideally suited for GND filters are those with simple lighting, such as the linear blend from dark to light commonly found in landscape and seascape photography.

GND filters come in many varieties. The first important setting is how quickly the filter blends from light to dark, which is usually termed “soft edge” or “hard edge” for gradual and more abrupt blends, respectively. These are chosen based on how quickly the light changes across the scene, where a sharp division between dark land and bright sky would necessitate a harder edge GND filter, for example. The standard soft edge is almost certainly the filter you would use.

Haze & UV filters – Nowadays 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. Digital camera sensors are nowhere near as sensitive to UV light as film, therefore UV filtration is no longer necessary.

For digital cameras, questions are asked if the advantage of a UV filter (protection) outweighs the potential reduction in image quality. For very expensive lenses, the increased protection is often the determining factor, since it is much easier to replace a filter than to replace or repair a lens.

Cooling or warming filters change the white balance of light reaching the camera’s sensor. This can be used to either correct an unrealistic colour cast, or to add one, e.g. adding warmth to a cloudy day to make it appear more like during sunset, although this effect can also be produced in most DSLR cameras and in editing software.

These filters have become much less important with digital cameras since most automatically adjust for white balance, and this can be adjusted afterwards when taking photos with the RAW file format. Some situations still need colour filters, such as situations with unusual lighting or underwater photography. This is because there may be so much monochromatic light that no amount of white balance can restore full colour.

Special effects filters – There is a massive selection of special effect filters on the market as well, including star filters (Star filters are simply designed to produce stars on your images from points of light sources), fog filter (When shooting real fog you will notice that the fog blurs the light source(s) in your image. The fog filter attempts to recreate that same effect), centre spot filters (The idea of a centre spot filter is that the centre of the image will stay nice and sharp while the rest of the image is diffused and the detail in the background is blurred), Enhancing Filters (also known as Intensifying and Didymium filters, are designed to increase the intensity and saturation of red objects. They are all designed to provide better colour saturation and contrast on the red, brown and orange colours without effecting the cooler range of colours), graduated colour filters, prism and close up, and probably many more.

So, do you need a special effects filter? An alternative is to shoot RAW and edit the colours afterwards – it’s easier and cheaper. If you shoot JPEG Photoshop contains a handy warming (and cooling) filter built into the program.

Problems with lens filters – Filters should only be used when necessary because they can hugely alter the image by introducing an additional piece of glass between your cameras sensor and the subject, this means they have the potential to reduce image quality. This usually comes in the form of either a slight colour tint, a reduction in local or overall image contrast, or ghosting and increased lens flare caused by light inadvertently reflecting off the inside of the filter.

Filters may also introduce physical vignetting (light fall-off or blackening at the edges of the image) if their opaque edge gets in the way of light entering the lens. Stacking filters therefore has the potential to make the above problem much worse especially on wide angle shots.

Notes on choosing a filter – Lens filters generally come in two varieties: screw-on and front filters. Front filters are more flexible because they can be used on virtually any lens diameter. Screw-on filters can provide an air-tight seal when needed for protection, and cannot accidentally move relative to the lens during composure. The main disadvantage is that a given screw-on filter will only work with a specific lens size. Also in the case of graduated, some lens rotate during focus which then misaligns the filter.

The size of a screw-on filter is expressed in terms of its diameter, which corresponds to the diameter usually listed on the top or front of your camera lens. This diameter is listed in millimetres and usually ranges from about 46 to 82 mm for digital SLR cameras. Step-up or step-down adapters are available so a filter can be used on a lens with a smaller or larger diameter. Care must be taken if using these, step-down filter adapters may introduce unwanted vignetting (since the filter may block light at the edges of the lens).