After you wet your feet in photography, you start exploring the other avenues that are available in photography, such as Astrophotography, Macro-Photography, Wild-Life Photography, Low-Light Photography, etc. Of this Low-Light Photography literally enthralls the viewers, with breath-taking photographs of the things, or rather how they look under night-lights.
The bridge, which looked mundane under sun-light, looks exotic, totally shining under warm glow of tungsten lights that come up when the Sun-goes down. This throws out many interesting subjects. Take for example, the lights from the automobiles, racing across the bridge, or on busy through-fare, they create spell-binding light trails which look like streaks of tungsten light and red-lights. The buildings which are firmly rooted show themselves in their shimmering glory. Any thing that is moving disappears from the view no matter how crowded the street or highway is. That is the magic of slow shutter-speed photography.
However, to create magic, shutter speed should drop to 1 second and below. This is not possible when the Sun God is shining in His blinding glory. We humans can only lessen the harshness of the light by wearing the dark Goggles. Companies like Rayban minted billions by catering to this need. So, the photographers
If you want to see the water cascading down a water-fall, look like a fluffy cloud of water coming down and falling on the rocks below, you have to get a goggle for your camera…….!! This goggle cuts the light intensity and turns day into twilight or day-break. This will fool your camera and make it slow down the shutter speed and create magic.
When you go to sea-shore you can make the water look like a super-soft shimmering satin by using the “Goggle “ for your camera ! This goggle we photographers call as Neutral Density Filter. This is supposed to be a shade of black, more dark it is, more light it will cut-off and bring down the shutter speed drastically. This ability to cut light is measured in terms of number of stops from the normal exposure. One stop less means the light is cut into half of its intensity, two stops means it is down to one fourth of the original intensity. Hence these filters are identified by the number of stops it can bring down the intensity of light.
There are some well-known companies who manufacture such filters. SRB, LEE, HOYA, FORMATT-HiTECH, COKIN,B+H are some of them. These filters should be such that they should only reduce the intensity of light and they should not introduce any extra colour into the image. These filters are available in various densities. Some cost you the earth, and some are affordable. You should go for such a filter!
We photographers are always looking for hacks and some of us use anything that can cut the light, such as welder’s glass, your dark goggles, etc. If you know photoshop then even if you use Do-It-Yourself type of “Jugad” to cut light, you can recover back!
These ND filters are classified as per its ability to cut light by number of stops, but there is one more way of measuring it and it is in terms of its optical density. For example a ND filter with optical density of 1.2 cuts light by 4 F stops ans is also numbered as ND 16. Just to confuse you further it transmits through only 6.25 % of light falling on it.
Hence whenever buying online , you may be misled by various parameters. Just to be sure, ask them by how many F stops it cuts down the light.
There is one more variety of ND filter is available and it is known as variable ND filter with this you get variable density for cutting light. This is generally made by two rotating polarizing filters put together. However purists in photography say that it is not a classical one. However when you have to choose between filters costing the earth and via-media for getting similar results, the choice is yours.