The Ultimate Guide To Landscape Filters: Neutral Density Filters

Sarah Howard, from Image Seen, has put together a comprehensive guide on filters landscape photographers should have in their camera bag and in part four, ND Grads are Sarah's focus. Take a look at the previous instalments to see what you've missed so far:

• UV And Skylight Filters
• The Polarising Filter
• The Neutral Density Graduated Filter

Keep checking FilterZone for the next instalment which will look at Ten Stop ND filters. 

Neutral Density Filters

One of the lesser known and underappreciated filters; neutral density filters have great creative potential. Semi, opaque, they are used to reduce the amount of light entering the lens, thereby prolonging exposure times, and making them useful aids when photographing water, clouds, or indeed anything moving when the intention is to convey movement rather than freeze it.

The beauty of ND filters is that they allow you to set the aperture and shutter speed you want, rather than that which the conditions dictate. Although they obstruct incoming light, they do so uniformly across the entire frame, therefore neither image colour nor contrast is affected. The effect of the ND filter cannot easily be reproduced digitally.

Types of ND Filters

There are several types of ND available - screw in ones which come in various filter threads and square or rectangular slot in ones which fit into a holder that attaches onto the front of the lens. The screw in type is the simplest to use but the slot in variety, can be used in conjunction with other filters in the same holder. There is also a variable ND filter available, which is screw in, but comes with an adjustable outer ring that you rotate to adjust the density, dependent on the light conditions and the effect you want.

ND filters are available in different strengths, the stronger the filter the more light it absorbs and the darker it appears, for example;

• 0.3/2x - one stop reduction in light
• 0.6/4x - two stops reduction in light
• 0.9/8x - three stops reduction in light
• ‘Big Stopper’/1000x - ten stops reduction in light

So for example, an ND4 will reduce the amount of light entering the lens by two stops. A ten-stop filter will produce an extreme increase in exposure time even in broad daylight making for some interesting creative effects.

The use of an ND filter has smoothed away any texture in the water giving it a glassy finish.

When To Use Them

Water

Using an ND will allow you to capture the flow of water. On waterfalls they prove useful in showing movement of the water to produce a silky effect. This can also be used on seascapes, with crashing waves for example, to produce more of a misty look. The speed at which the water is moving as well as the light conditions at the time will dictate the filter you choose, along with your own personal preference of course.

People

ND filters can be used very effectively to get rid of unwanted people in the frame, for example when shooting in popular tourist spots. As long as they are moving if the shutter speed is slow enough it will ensure they are blurred are not visible in the image. An exposure of a few seconds is needed to achieve this.

To retain aperture

If shooting in bright conditions, it can occasionally be impossible to take a photograph at the aperture and depth of field you desire. For example, if you want to capture a flower and throw the background out of focus, you’ll need a wide aperture, however your camera may well be suggesting something along the lines of F16 or 22 which isn’t going to give you the depth of field you require. Using an ND filter will reduce the amount of light entering the lens, prolonging the exposure, and allowing you to select a wider aperture to give you the result you want.

The use of an ND and polariser filters has brought out the green of the vegetation and given the waterfall a silky look.

What To Watch

1) Choose with care - as with most things you get what you pay for. Polyester is the cheapest material but gives poorer results, often producing a colour cast, although this can be removed in post processing. Glass is prone to breaking, so the ideal choice is resin.

2) Circular filters are limiting in that they only fit a specific diameter lens, unless you buy step up rings, meaning you may have to buy more than one.

3) Vignetting – stacking of filters can lead to vignetting issues, particularly with wide-angle lenses. Make sure if using a slot-in filter holder, that you buy a wide-angle adapter ring.