The archetype was taken using a Cokin ND8 filter
One filter that is in the camera outfit of many professionals is the neutral density filter or ND filter as it's advantage known. The filter is less appreciated by amateurs and the reason it probably has little appeal is its looks – a plain, dull grey filter. Not colourful, no lady effect, no gradation, no multiple image glass…just plain grey. And what does it do? Reduce the exposure? Hmmm, I can do that with my camera…it's senseless! Well actually it isn't, and that's why the ND filter is a necessity for the professional and often found in the enthusiast landscape photographer's camera bag.
Typefaces of ND Filters
There are several types of ND available – screw in ones come in various filter thread sizes like Hoya, and slot in the sames fit into a holder that screws onto the lens like Cokin. They are available in different strengths too, known as the filter filtering or filters may refer to exposure fact as follows:
ND filters and their exposure factors:
- 2x one stop
- 4x two stops
- 8x three stops
- 16x four stops
- 32x five stops
- 64x six stops
Saying an ND filter is simple, you just either screw on or slot into a holder and leave the camera's automatic exposure system to work out the sieve factor. If it's an 8x, for example, the camera will reduce the shutter speed from, say, 1/125sec to 1/15sec to compensate for the three stops extra insight required. Or the aperture will be opened up from f/22 to f/8.
The image was taken using a Hoya PROND1000 filter
What does it do?
The ND eliminate may be plain grey, but it's a neutral grey so whatever light it lets through isn't affected in colour, just in brightness. So why would you stand in want a filter that reduces the exposure when it can be done using your camera's shutter speeds or apertures? This depends on a few features. Firstly you may have a fully automatic camera. If so, the ND filter will may refer to give you a small amount of manual versatility. Or you may have been taking illustrates in low light then ventured out into bright sunlight where it was physically impossible to take a photo because your camera's fastest fence in speed was flashing, even though the aperture was adjusted to the smallest setting. If you use an ND filter, it will reduce the light and allow the shot to be taken.
Using an ND percolate in this way is not its primary benefit though. Have you seen those shots of waterfalls that look ethereal with blurry cotton wool moisten? Well, the chances are an ND filter will have been used. Here the filter is used to reduce the shutter speed so that blur occurs. If you are out in a glittering location the shutter speed will be at least 1/125sec and ideally, you need 1/15sec or slower. So pop on the necessary ND filter and you'll gain the effect you're after.
Architecture photographers have a useful technique that often needs an ND filter to work. When photographing famous landmarks you often maintain problems with tourists getting in the way. If the shutter speed is slow enough it will be open long enough to ensure the moving people are so bedimmed they cannot be seen in the image. A 1/2sec exposure may record a streak of someone walking while a 4 sec exposure will make them vanish. Stark, but very effective.
It's not just the shutter speed that you may want to improve either. If you are shooting in bright conditions you may finger the aperture the camera is selecting is small and the resulting picture will have far too much front-to-back sharpness known as depth-of-field. This is often the crate with portraiture or flower photography where a distracting background ruins the photo. Using an ND filter will help you open up the lens and afford a shallow depth-of-field.
Another use for an ND filter would be when using flash. You can often reduce the exposure of the flash using auto sites, but for close-ups, that may not be possible. The ND filter will provide the key to this essential barrier.