KNOW HOW: Let There Be (Less) Light!

For the uninitiated it might seem bizarre that you would want to pay money for an accessory that actually reduces the amount of light coming into your camera, but there are indeed some very good reasons why the Neutral Density, or ND, filter has a crucial role to play in the worlds of both stills and film, and many serious operators would never leave home without one.

What are they?

It has to be said that, on first inspection, the ND filter looks like a pretty unprepossessing piece of kit. It’s a plain, dull grey piece of glass or gel, and when you look through it nothing spectacular happens: you just have a slightly dimmed down view of the world, with no effects whatsoever. But that’s actually the whole point, and what you’re paying for is the fact that there genuinely should be nothing going on apart from a precisely quantifiable amount of light that’s been held back. You don’t want a starburst or a colour cast, just a longer exposure time, and it’s actually quite a feat to produce a filter that’s capable of being so totally neutral.

What types are there?

You realise fairly early on that not all ND filters are the same. Far from it in fact, and most serious photographers and filmmakers will have a selection of them that they carry. They are offered in a variety of filter thread sizes or maybe as a sheet of gel that slots in a holder screwed into the front of the lens, and they come in a variety of strengths. A 2x ND Filter will create a one-stop drop in exposure, a 4x gives two stops, an 8x three stops and so on.
The Marumi range distributed by Kenro offers values that start at three stops and move on from there at one stop increments, up to 64x, which makes six stops of difference. That might sound like a lot, but in recent years there has been a growing demand for an even stronger effect, and Marumi has now risen to the challenge with the launch of a Super ND 500 and 1000, which reduce exposure by nine and ten stops respectively, and these come in a range of filter sizes from 49mm up to 82mm.

Making a difference

To put those figures into some sort of perspective, six stops of difference will take you from an f-stop of f/16 – really closed down, as it might be on a sunny day – through to f/2, which is as wide open as many lenses are able to go. Similarly, that kind of difference on the shutter speed front will see you go from 1/500sec – enough to freeze all but the fastest of movement – down to 1/8sec, a speed where moving subjects will be heavily blurred. Go for the full ten stops and your shutter speed will be down at two seconds, enough to allow for some really creative effects.

Specialist filters

The variety of options provided by ND filters gives a clue as to their popularity. For those that don’t want to carry a selection of filters the best choice is an ND variable filter, such as the Marumi ND2-ND400, which enables continuously variable light adjustment from one stop through to nearly nine stops, all in a single device. You simply twist the filter in the way you might do a polarising filter to increase or decrease the effect.
Marumi even produces a special DHG ND100K ND filter that’s specifically designed for taking photographs of a solar eclipse, and this is capable of reducing light values up to 1/100,000 times. Limited to use with telescopes and cameras – it’s not suitable for eye protection – you might only have cause to use it on very rare occasions, but at these times it could be the only way to achieve the images you want.

What do ND filters do?

There are a surprising number of occasions when it might be useful to be able to hold back a little, or a lot, of the light in front of your camera.
  • On a really bright day, for example, you might have areas of the scene that are ‘burning out’ or overexposing, and an ND filter will enable you to lower the overall contrast of the scene and to get the picture you want.
  • ND filters give you way more control over apertures, which is useful if you aren’t looking to produce an image where everything is in focus from the foreground through to the distant horizon. On a bright day you might be working at your smallest f-stop, in which case depth of field will be immense. Drop this back five, six, seven stops or more and suddenly you could be working at your maximum aperture, and focusing tightly to create a dramatic rim of sharpness, surrounded by glorious bokeh. 
  • Shutter speed can also be controlled by the use of ND filters. Landscape photographers are regular users of this accessory, since it allows them to heavily influence the appearance of the picture they’re taking. This is where the really strong ND filters can come into play, and a nine or ten stop difference can take you into the realm of an exposure that’s several seconds long. This is enough to turn running water into a sumptuous, milk-like blur, while static areas of the scene are rendered crisp and sharp. Think of a waterfall, for example, which can come to life in a still frame through the use of a slow shutter speed. You can also make clouds scud across a sky in the same way, the branches of trees come alive in the wind or shoot a scene at night where the lights of passing vehicles become abstract streaks of colour.
  • Say goodbye to crowds. Architectural photographers who have a mission to achieve a shot of a building without people in front of it can sometimes achieve their end by setting an exposure that’s several seconds long and then waiting for the movement of people to effectively make them disappear from the scene. You need a very steady tripod for this technique to work, but it can be surprisingly successful.

ND filters for filmmakers

The ND filter is every bit as important to filmmakers as it is to still photographers, with many of the higher end cinema cameras actually having them built in for ease of use. They do have a different job to perform, however, and in the world of filmmaking it’s all about being in control of the amount of light entering the camera to maintain the shutter speed or frames per second (fps) rate you want to be shooting at.
You could, of course, adjust the fps rate or the aperture to control the light, just as you would on a still camera, but on a movie this would be less of an option since you’re looking for consistency, and you don’t want the feel of your footage or your depth of field noticeably changing from shot to shot. So the ND filter becomes your control tool of choice, and by using this carefully you can maintain both your fps and aperture at the same level throughout your shoot, however much the light might be changing throughout the day.

So, it can be seen that this simple accessory has a very great deal more to it than might originally appear to be the case. Being such a well priced piece of kit, it’s something that pretty much every photographer or filmmaker should be looking to acquire at some point, even if it’s just to see what extra creative touches it might allow you to add to your work.

Tuesday, 30 January 2018