Top 5 essential photography filters (and why you can't live without them!)

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Even though you can achieve many effects in Photoshop , here are five photography filters that no photographer should be without...

It's all too easy to think that filters are old-fashioned and unnecessary, but there's a lot to be said for still using traditional filter effects.

Some photography filters, such as polarisers and strong neutral density filters, can produce effects that are time-consuming or even impossible to replicate digitally, while others, like the humble skylight filter, enable you to shoot in conditions that could otherwise damage your lens.

So, don't rely on Photoshop for all your effects; get out there and have fun the traditional way with the five filters that every photographer should own. They will literally transform your images overnight...

Round or square filters? 
There are two basic types of filter design - round ones that screw directly into the thread on the front of a lens, and square ones, which slot into a filter holder that you need to attach to the lens via an adapter ring (which is again screwed into the front of a lens).

Round, screw-in filters are ideal if you only want to use the filter on one lens, or lenses with the same size thread, but if you have lenses with different thread sizes you'll need different filters for each one.

With the square filter system you only need to buy one set of filters, as these can then be attached to the lens using adaptors of different sizes.

Which type you should choose also depends on the type of filters that you want to use, as some filters are only really useable screwed directly to the lens or in a square filter system.

Skylight filters, for example, are best suited to the round screw-in design, but filters such as neutral density grads are easiest to use in a square filter system.

Essential photography filters: 01 Skylight filter

What's it for? 
Protecting the front element of your lens from damage or dirt

What's the technique? 
A skylight or ultraviolet filter is mainly used to protect the front of your lens from potential damage, and prevent you getting dirt, dust or water on the (harder to replace) front element of the lens.

All you need to do is keep the filter attached to your lens whenever you are using the camera. This is particularly important when shooting in wet, muddy or dusty conditions.

UV and skylight filters also filter out some ultraviolet light, which has the effect of reducing haze. Unlike a UV filter, a skylight filter has a very subtle pink cast to it.

This was originally designed to reduce the slightly blue cast of colour film, but with digital cameras this isn't really an issue.

Even though this filter will prevent the worst of the dust, dirt and water reaching the front of the lens, you may still need to clean the filter to prevent this dirt affecting your images.

For dust and dirt it's best to use a brush or air blower to remove this without damaging the filter.

If you try to wipe the filter clean there's a risk that you'll scratch the surface. Wiping the filter to remove water drops needs to be done extremely carefully, as it's likely that there will also be some dirt or dust that can become embedded in the cloth or tissue, and scratch the filter.

Round or square? 
Because they are primarily for keeping attached to your lens for protecting the front element, round, screw-in skylight or UV filters are the best option.

Essential photography filters: 02 Polarising filter

[caption id="attachment_553710" align="aligncenter" width="610"]Shot with a polariser[/caption]

What's it for? 
Increasing colour saturation and reducing reflections in non-metallic objects

What's the technique? 
Polarising filters come in a rotating mount, as their effect varies as you turn the filter. So, once you've attached the polariser, and framed your shot, you need to slowly rotate the filter while watching the effect through the viewfinder or in Live View.

You will see reflections in non-metallic objects such as water or glass appear and disappear as you rotate the filter.

The filter will also increase the colour saturation, and darken blue skies, giving greater contrast between any sky and clouds.

This isn't always immediately obvious, especially through the viewfinder, so you might need to rotate the filter more than once to judge the best orientation for the effect that you want.

[caption id="attachment_553708" align="aligncenter" width="610"]Shot without a polariser[/caption]

The effect is usually at its most obvious when you're shooting at right angles to the sun, rather than with the sun behind or in front of you.

When using a polariser on a wide-angle lens, particularly if you're shooting blue skies, you need to watch-out for darker 'bands' appearing in the sky due to the polariser darkening the sky unevenly.

If this occurs you should rotate the filter until this disappears, or even consider removing the filter altogether.

Round or square? 
As you need to rotate the filter to adjust the effect, polarisers are most commonly found in the round, screw-in design, which is why they're often referred to as circular polarisers, or CPLs.

They're available for some square filter systems, such as the Cokin P series, though. There are also polarisers available for systems such as the Lee 100mm system, either as a standard square version or a 105mm round filter that fits on a circular mounting ring in front of the holder.

The latter are perfect for using with graduated neutral density filters (see filter 04), but they're very expensive.

Essential photography filters: 03 Straight neutral density filter

[caption id="attachment_553712" align="aligncenter" width="610"]Shot with a straight neutral density filter[/caption]

What's it for? 
Allowing you to use longer shutter speeds or wider apertures than would otherwise be available in the prevailing lighting conditions

What's the technique? 
A straight neutral density, or ND, filter is essentially a 'darkened' sheet of glass or resin that reduces the amount if light entering a lens, and therefore reaching the sensor.

Think of it as a pair of sunglasses for your camera! Crucially, it reduces the amount of light reaching the sensor without affecting the colours, hence the term 'neutral'.

Using straight neutral density filters is easy as you don't have to worry about positioning the filter, and in most lighting conditions you can still use the metering and focusing systems in your camera.

[caption id="attachment_553707" align="aligncenter" width="610"]Shot without a straight neutral density filter[/caption]

First, with your camera set to its lowest ISO, you need to frame your shot, and then select the shutter speed and/or aperture to give the creative effect that you want (such as a slow shutter speed in the case of blurring movement).

So, for example, you might want to blur a waterfall by setting a shutter speed of 2 secs, and keep everything sharp from front to back by setting an aperture of f/16.

In bright sunlight (or even in overcast conditions) these settings would result in a badly over-exposed image, because a two-second exposure would simply let too much light through to the sensor.

Setting a much faster shutter speed would help, but then the waterfall wouldn't be blurred. Reducing the aperture would help, too, but even f/22 or f/29 wouldn't be small enough for a correct exposure when the shutter speed is so slow, and f/29 is as small as many lenses go.

The other way to darken exposures is to make the sensor less sensitive by decreasing the ISO, but if you've already set ISO100, you can't go any lower (some cameras will go as low as ISO50, but again, this wouldn't be low enough in our example).

This is where a straight ND filter comes in: NDs come in different strengths or densities, most commonly reducing the light by one to three stops.

For most lighting conditions, a three-stop filter, also known as a 0.9 or ND8, is suitable, though in very bright conditions, you may need an eight- or even a ten-stop filter, such as Lee's Big Stopper.

In our example, a waterfall in bright sunlight would need a shutter speed of 1/125 sec at f/16 and ISO100 for a correct exposure. To use a shutter speed as slow as 2 secs, you would need to reduce the amount of light reaching the sensor by eight full stops (i.e. 1/125 sec > 1/60 sec > 1/30 sec > 1/15 sec > 1/8 sec > ¼ sec > ½ sec > 1 sec > 2 secs).

Round or square? 
Because you don't need to change the position or orientation of straight ND filters they are available in both round and square designs.

If you don't want to use them with other filters the round, screw-in designs are perfect, but if you want to use graduated neutral density filters at the same time it's better to go for filters that fit the same holder as the grads.

Essential photography filters: 04 Graduated neutral density filter

[caption id="attachment_553705" align="aligncenter" width="610"]Shot with a graduated neutral density filter[/caption]

What's it for? 
Balancing the exposure between a bright sky and a darker foreground, particularly in landscapes and sunrise/sunset shots.

What's the technique? 
To use our previous analogy, a graduated neutral density filter, or ND grad, is like a pair of sunglasses with dark glass at the top and clear glass at the bottom.

By placing the dark part of the glass over a sky that's much brighter than the scenery below, and lining the transition up with the horizon, you can ensure a balanced exposure.

ND grads come in several different strengths, and with different transitions between the dark and clear areas.

For most uses a two-stop grad, also known as a 0.6 or ND4 grad, is a good option, but for shooting sunrises or sunsets with the sun in the frame, you may need an even stronger filter, such as a three-stop (0.9 or ND8) grad, to give a more balanced exposure.

[caption id="attachment_553706" align="aligncenter" width="610"]Shot without a graduated neutral density filter[/caption]

There are two main types of transition between the dark and clear areas: hard or soft. Hard grads go from clear to dark very suddenly, so are best for subjects with a clear, uncluttered horizon, such as seascapes.

Soft grads feature a much more gradual change from clear to dark, and are suitable for landscapes where there are trees, mountains or buildings above the horizon.

Once you have attached the filter holder to your lens via the lens thread, you simply slide the ND grad into the slot closest to the lens. You then have to move the filter down while looking through the viewfinder (or at the LCD in Live View) until you see the whole sky darken.

The critical area is just around the horizon - you'll need to fine-tune the position of the filter so that the transition between the clear and dark areas lines up with the horizon, otherwise you'll end up with a very bright strip of sky or a very dark strip of land near the horizon.

Round or square? 
Because you need to move the filter up and down, the square filter system is the only option for ND grads.

Essential photography filters: 05 Variable or strong neutral density filter

[caption id="attachment_553714" align="aligncenter" width="610"]Shot with a strong ND filter[/caption]

What's it for? 
Using extremely long shutter speeds or very shallow depth-of-field effects in bright conditions.

What's the technique? 
A variable ND filter is similar to a straight ND filter, but as the name suggests, with a variable filter you can vary the strength or 'density' of the filter by rotating the filter elements.

While the effect of using a variable ND filter at the higher strengths are the same as using a strong plain ND filter, you use them in slightly different ways.

[caption id="attachment_553709" align="aligncenter" width="610"]Shot without a strong ND filter[/caption]

With a variable ND filter, you can attach the filter before you frame the shot, focus and set the exposure.

This is because you can adjust the filter to its lowest strength to start with, allowing you to see clearly through the viewfinder to focus and compose your shot.

Once you have set-up the camera you can then adjust the filter to a higher strength before you take a shot.

A very strong ND filter, by contrast, is so dark that it's almost impossible to see through once it's in place, so you will need to set the camera up before attaching the filter.

With either type of filter you will need to set the camera to manual exposure and manual focus, and if you are using long shutter speeds, you will also need to fix the camera to a tripod to avoid camera shake.

SEE MORE: 10 common landscape photography mistakes every photographer makes

Round or square? 
Variable ND filters are usually round filters that you screw on, while strong, single-strength ND filters are available in both round and square formats.

When using single-strength filters, however, you'll find that it's quicker and easier to remove and replace the filter when framing, focusing and metering if you're using a square filter system.

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