While somewhat useful to stills photographers, variable ND filters are an indispensable tool for filmmakers. This filter allows quick and easy manipulation of the exposure in order to achieve the desired aperture and shutter speed when there is too much light.
Variable ND filters are made by mounting two polarisers facing each other and when turned, they progressively cut out more and more light. This can achieve an exposure reduction ranging from 1.5-10x stops, so why is this filter limited to a maximum of 5x stops exposure reduction? The problem with the double-polariser approach is that beyond a certain range, the darkening becomes very uneven across the frame, resulting in what is known as the x-effect - see image x. This is why most commercial film productions still make use of conventional ND filter sets.
A Variable ND filter does however still have a great place in the world if used within the limits of the x-effect, which is why NiSi have limited their offering from a 1.5x - 5.0x stop range. Compared to a conventional cinema ND filter set and matte box with filter trays, this filter costs about 5% of the price. It also offers instant manipulation of the exposure reduction by simply turning the filter and thanks to its compact size it is much more friendly to DSLR and mirrorless filmmakers.
This filter features NiSi's renowned scratch-resistant and hydrophobic nano-coating, which ensures that it lasts and makes it quick and easy to clean. It also features a pin on the side that makes it easy to rotate from behind the camera.
Is there any X-effect at 5 stops?
If you set out to look for it, you will encounter a hint of the X-effect at 5 stops...if you use an ultra-wide lens and you shoot against a clean background. Our staff have used this filter for countless video productions and we have been selling it for a year, without noticing the X-effect in any of our videos or receiving one complaint about it from a customer. So while you might find it if you really look for it, it simply doesn't show up in practical use.