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.
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
Shot with a polaris
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.
Shot without a polariser
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.
Essential photography filters: 03 Straight neutral density filter
Shot with a straight neutral density filter
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.
Shot without a straight neutral density filter
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).
Essential photography filters: 04 Graduated neutral density filter
Shot with a graduated neutral density filter
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.
Shot without a graduated neutral density filter
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.
Essential photography filters: 05 Variable or strong neutral density filter
Shot with a strong ND filter
What’s it for?
Using extremely long shutter speeds or very shallow depth-of-field effects in bright conditions.
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.
Shot without a strong ND filter
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.