Variable Neutral Density Filter

Variable Neutral Density Filters are one of my favorite new photography tools. Just like a traditional Neutral Density (ND) filter these filters let you restrict the amount of light entering your lens, which is important if you are shooting on a bright sunny day or looking to have an extra long exposure. But, as the name implies, a 'Variable' Neutral Density Filter lets you block differing amounts of light.

Before Variable Neutral Density filters came along you had to carry around a number of different grade ND Filters which each blocked out a specific amount of light. However, a single Variable ND filter can replace an entire set of old Neutral Density Filters.

Variable ND Filters give you more than just convenience and a lighter camera bag. With a set of old ND filters you can only block out light at specific steps, while a new Variable ND filter lets you block out light at amounts in between these steps. This is like using a camera that lets you only set the aperture at each of the f-stops versus one that lets you set the aperture at each 1/3 of an f-stop.

Variable Neutral Density filters are circular glass filters which consist of two lenses, a back lens which is fixed and a front lens which can be rotated. As you rotate the front lens the alignment between the two lenses changes blocking more or less light.

You can see the same effect by staking two polarizing filters on top of each other rotating one of the lenses.

While this trick can work in a pinch, it is not very practical as you will get vignetting around the edges of your photograph from stacking the two filters.

As with all filters it is important to get the highest quality that your budget can afford. It makes no sense to put a cheap filter on an expensive lens as your optics are only as good as its weakest link.

This is no different when purchasing a Variable Neutral Density Filter. Lower quality Variable ND filters will not evenly block light throughout the light spectrum. This result in photographs with a particular color tint to them, which will get worse when the amount of light blocked is increased. With a cheaper Variable Density filter photos taken with minimal light blocked may be fine, but ones taken closer to the maximum may be unusable.