If you're an experienced photographer, the chances are you have a collection of filters for your camera, to extend your shooting options. Although you can create all manner of photographic effects using image editing applications nowadays, some can't be replicated using software alone, or at least not as well. The same is true of camcorders. For this reason, virtually all camcorders have a lens screw for fitting a filter, although the thread diameter will vary from model to model. Any photographic filter can be used with a camcorder as well, so long as the thread diameter matches. But only a few filters are actually worth adding to your arsenal.
The most useful filter of all for a camcorder is Neutral Density (ND). This simply reduces the amount of light entering the lens equally across the spectrum, a bit like giving your camcorder dark glasses. This may seem like a strange thing to do, but it has an important knock-on effect. When shooting in bright conditions, if you leave your camcorder to configure exposure automatically, it will generally use the minimum aperture and a high shutter speed. Even in manual mode, you will be forced to choose between a very high shutter speed, or minimal aperture - and you may have to use both.
So if you want a soft motion blur look, rather than pin-sharp frames, this won't be possible in very bright light. Even with the minimum aperture setting a lower shutter will cause overexposure. Conversely, even the camcorder's top shutter speed might not allow an aperture much larger than the minimum. The smaller the aperture, the larger the depth of field, so a greater range in front and behind your subject will be in focus. In other words, shooting in bright conditions will leave you stuck with sharp images from the fast shutter, and more of the background in focus, which can lead to a rather flat look.
This is where the ND filter comes in. By reducing the amount of light entering your camcorder's lens, it will allow you to reduce shutter or aperture, for greater shooting flexibility. This is such an essential function that most professional camcorders have a Neutral Density filter built in, so you can simply pull a lever to apply two or more levels. But consumer camcorders don't, so you will have to buy a separate filter and attach it yourself.
The strength of a Neutral Density filter is usually expressed by its Attenuation factor, with common values ranging from 2 to 64. A 2x ND filter will reduce the effective F-stop by 1, cutting out 50 per cent of the light entering the lens. A 64x ND filter is 32 times stronger, and therefore reduces light transmission to around 1.5 per cent, or 6 F-stops. It's not a particularly expensive item to add to your arsenal. You can pick up a 4x Neutral Density filter from Keene Electronics for just £9.99, with most popular thread diameters represented. Jessops has a wider range of options, but these are generally more expensive.