Using ND, ND Grad and Polariser filters
Often dismissed as either unnecessary or gimmicky, filters can be the most important and useful creative tools in your camera bag. But which types of filters are actually going to enhance your images, and how do you choose between the different filter systems? Here we show you how ND filters, ND grads and polarisers can transform the look of your images.
Best photography accessories for under £100: neutral density filters
ND filters reduce the amount of light entering the lens. While the technology is simple, the effect on your images can be amazing.
ND filters can be divided into two main types according to the strength of the filter. The cheapest and most common filters reduce the light levels by one, two or three stops, and are useful for subtle effects.
In recent years some much stronger filters have become readily available that will reduce the light by up to ten stops, making extremely slow shutter speeds possible even in the brightest conditions.
One of the most popular uses for this filter is to achieve the classic milky water and blurred cloud effect without having to wait until after dark.
But it can also be useful when shooting in situations where you want to remove people or traffic moving across the scene.
Standard one-, two- and three-stop ND filters are much easier to use than stronger ND filters because you can still meter, compose and focus with the filter in place in bright conditions.
They are useful when you want to use wide apertures in bright conditions for shallow depth-of-field effects, or for extending the shutter speed around dusk where a stronger filter would give an exposure time of several minutes.
How to use a strong neutral density filter
1 Compose your shot
With the filter on you won’t be able to see through it to compose your image, so you need to set up your shot beforehand. With the camera on a tripod, compose your image, then lock down the tripod, and adjust settings as appropriate.
2 Set manual exposure and focus
In many conditions the metering in the camera won’t be able to measure the exposure once the filter is attached, so you’ll need to work out the exposure manually. Switch to manual exposure mode and meter for the scene.
3 Attach the filter
Attach the filter and adjust the shutter speed to suit the new exposure needed. This can get pretty complicated – for each stop you need to double the exposure time. Using a nine-stop filter like the Light Craft Workshop ND500MC, you need to multiply the original exposure time by 512 to get the correct exposure.
ND numbers explained
Filter systems explained
ND filters are available in either round or square designs. The round filters simply screw onto the front of your lens, while the square type need a holder and an adapter ring to attach them.
Choosing between the two systems depends on the type and number of filters you’re likely to use, and also the lenses you’ll want to use them with.
Round filters are ideal for using individually, and if all your lenses have the same filter thread size.
Square filters are better suited for using more than one filter at a time, or if you own a range of lenses with different thread sizes.
Buying the whole system for square filters can be very expensive, but as a stopgap you could consider simply holding the filters in front of the lens.
You need steady hands and the camera on a tripod for this to work, and it won’t be easy to hold the filter still for exposures of a second or more.
Another solution is to use a tiny amount of Blu-Tac to help keep the filter in position while you hold it.
Square filter systems
There are three main systems, and they all comprise three main components: the filter, a filter-holder, and screw-in adapters of different sizes to fit different-sized lens threads. Some are interchangeable, so a Cokin Z-Pro filter will slot into a Lee holder, but the adapters are specific to each holder.
These 85mm filters offer a good value route into square filter systems, but the size limits their use. The filters are too small to use successfully on many wide-angle lenses, or even large-diameter lenses, without causing vignetting in the corners of the frame.
The 100mm filters of the Cokin Z-Pro system make them a much better option than the P-series if you use (or are thinking of buying) a wide-angle lens. The filter holder is modular to vary the number of filter slots, which is particularly useful for avoiding vignetting on wide-angle lenses.
These are a popular option among pros due to their quality and consistency. Like the Z-Pro system, the filters are 100mm wide, and the holder is modular, allowing you to vary the number of filter slots, but the range of accessories you can attach to the Lee holder is greater.
Best photography accessories under £100: ND grad filters
alancing the exposure between a bright sky and a landscape is often impossible. Expose for the sky and the landscape will end up almost black; expose for the landscape and the sky will be far too bright. This is where ND grad filters come in.
These filters are half clear and half dark to enable you to reduce the light levels over part of a scene while leaving other areas unaffected.
ND grads come in several different types to suit different shooting conditions. The two main variables are the strength, which determines how much light the dark half blocks out (this is commonly measured in one, two, or three stops); and the so-called step, which determines the softness or hardness of the transition from clear to dark.
Hard-step ND grads change from clear to dark very abruptly. They are ideal for shooting subjects with a clear, straight horizon, or any other straight change from dark to light areas.
Any darker areas in the scene such as cliffs, trees or buildings that cross the horizon will be darkened by the filter. In these situations it would be better to use a soft-step ND grad.
With these filters the change from clear to dark is much more gradual. This means that they won’t darken objects above the horizon as much as the hard-edged versions, making them better for keeping detail in objects that are above the horizon or don’t have a well-defined transition between the lightest and darkest areas.
The effect of the transition is also affected by the aperture and focal length used; the narrower the aperture and the shorter the focal length, the harder the transition will be.
If you can only afford one ND grad and you shoot a range of subjects, go for a 0.6 (two-stop) soft-step filter.
How to use ND grad filters
Getting the most from ND grad filters takes a little practice…
1 Compose your scene
Before you go near the filter you need to finalise the composition of the scene, ideally with the camera on a tripod to make sure that it stays in this exact position.
2 Position the filter
This is where you need to take time to make sure that the dark area of the filter only just covers the bright area without affecting other areas of the scene. It’s sometimes impossible to avoid darkening areas such as cliffs, trees or buildings that cross the horizon.
3 Check the exposure
With the camera in manual exposure mode and the metering set to evaluative or matrix, take a test shot. Check the histogram to see whether the shot’s too dark (the histogram is shifted to the left) or too light (shifted to the right). Then adjust the exposure to retain the maximum tonal detail possible.
Best photography accessories under £100: Polarisers
Polarising filters are used to reduce reflections on non-metallic subjects, increase colour saturation and darken blue skies. Every outdoor or landscape photographer should consider having one of these filters in their bag.
When it comes to choosing one, make sure you get a circular polariser rather than a linear type, otherwise your SLR’s metering and autofocus systems won’t work.
Also, polarisers for the Cokin or Lee 100mm square systems are very expensive, so even if you have these systems it’s worth considering buying a screw-in polariser for your main lens.
The key to using a polariser is that the effect varies as you rotate the filter, so you’ll need to look through the viewfinder while rotating the filter to see how the image changes.
When you want to use a polariser to darken blue skies and make clouds look crisp and white, the effect will be at its most dramatic when you’re shooting at right angles to the sun.
When it comes to shooting water, you’ll see reflections in the surface appear and disappear as you move the filter, and you need to stop when the effect looks best.
This can take a little practice because the changes can be subtle, so take your time when rotating the filter.
One final consideration is that polarisers can reduce the exposure by up to two stops, so it can have a similar effect to an ND filter, allowing you to use slower shutter speeds than without the filter attached.
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Common problems caused by filters
The most common issues that can affect your images when using filters, and how to solve them
Vignettes are darkened corners in an image. They’re usually produced when using filters with wide-angle lenses, especially at wide apertures, because the wider field of view means the filter the holder is included in the image.
The best way to overcome this is to zoom in slightly until the edge of the holder is no longer in frame, or to decrease the aperture. If you’re using multiple filters you may need to remove some of them.
Flare can either be circles of light on your image or an overall lack of contrast. It’s most often caused by a dirty or damaged filter, and is usually produced when you’re shooting into the light, although it can occur at almost any time.
The solution is to simply clean the filter if it’s dirty, but if it’s damaged then replacing it is the only real answer. If you’re shooting with the main light source just outside the frame, you can minimise the effect by shielding the filter.
With screw-in filters you can use a lens hood to do this, but you can also use your hand or a small piece of black card. You need to be careful not to include this in the image, though.
This occurs mainly when shooting with a polariser on a wide-angle lens. It’s visible as a dark band of blue across one section of the sky. The only solution is to avoid using the polariser if you need to use an extreme wide-angle lens for your shot.
The best ND grads for under £100
Lee 0.6 Neutral Density Graduated Soft £80
SRB P-size ND Grad Kit £46
The best polarisers for under £100
Hoya Pro1 Digital Circular Polariser From £50
Kood Circular Polariser From £15
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