The Freewell Versatile Magnetic Variable ND filter system is the most innovative approach to building a filter I’ve seen. Not only clever, it works too. Optical filters are one of a few categories of photo/video equipment, perhaps along with tripods, and fluid heads that are not normally considered ripe for innovation. We rely on these foundational pieces of image making tech just about every time we take out a camera, yet they don’t change in principle design very often.
“If it ain’t broke, don’t fix it” definitely comes to mind when I think of optical filters. Something so complex in terms of materials, the ultra high quality optical glass, and sophisticated coatings, yet simple in design and function seems so ideally optimized already. Any likely change would certainly detract in some way from either form or function, right?
Freewell, already a top three favorite of mine with their magnetic variable ND filters, have not redefined what a variable ND filter is, or even the principles on which it functions, but the Freewell Versatile Magnetic VND definitely expands versatility, as the name suggests, and function, without compromising performance or ease of use.
Introducing the Freewell Versatile VND Filter System
The Freewell Versatile Variable ND Filter is a modular magnetic filter system which can be quickly and easily configured to perform multiple functions.
These functions are:
The system separates the two polarizing elements that are normally permanently stacked in any one piece VND filter, making it modular. By swapping the combination of these two optical elements, you can change the optical function.
The system is magnetic, comprising a base ring which threads onto any lens, plus an interchangeable base filter, and then an interchangeable second filter element which snaps into place magnetically over the base filter.
If you haven’t been directed here from my YouTube video, or haven’t seen the video. I encourage you to watch it. It introduces the Freewell Versatile VND Filter, all of its components, and how to use each of its functions.
Freewell Versatile Magnetic VND Filter Optical Performance
The most important thing to me with any filter, is how it affects color in my image. An ND filter, or variable ND filter, polarizer, or diffusion filter should all be spectrally neutral. This means it should affect all wavelengths (colors) of light passing through it equally.
The fact is, no filters are perfect, and filters which don’t cause noticeable color shifts in your image are in my experience always the most expensive. This is no different with the Freewell Versatile Magnetic VND filter. It does introduce color shifts, and moreso than the best VND filters I use but less than many filters costing more.
However, this color shift is easily corrected in post production if you shoot a simple color chart, such as the X-Rite Colorchecker, or any good video color chart.
Using a vectorscope and some simple Hue vs Hue and Hue vs Sat curve adjustments I can quickly correct the shifts in hue and saturation in DaVinci Resolve. Below you will find test examples before and after correction, showing the showing the shift on the vectorscope.
The circular polarizer is just the 2-5 Stop VND / CPL top filter, with CPL facing outwards, and no base filter installed. There is a shift in saturation towards yellow, which desaturates blue by about the same amount, and shifts the hue of red, magenta and cyan. Green is almost untouched. White, which is indicated by the central dot is not significantly shifted off center.
2-5 Stop Variable ND
The 2-5 stop VND comprises the VND base filter plus the 2-5 Stop/CPL top filter, with 2-5 Stop facing outward. There is a more pronounced increase in yellow saturation, with blue desaturated by about half as much as yellow saturation is increased. A more or less even shift in hue can be observed in all the other color chips, including green. Cyan, however is shifted more than the others and desaturated. White, which is indicated by the central dot is shifted very slightly off center towards yellow.
6-9 Stop Variable ND
The 6-9 stop VND comprises the VND base filter plus the 6-9 Stop/ND32 CPL top filter, with 6-9 Stop facing outward. The color shift follows almost identically to the 2-5 Stop VND, only in this case with stronger shifts in both green and cyan. White, which is indicated by the central dot is shifted very slightly off center towards yellow.
ND32 Circular Polarizer
The ND32 CPL is just the 6-9 Stop / ND32 CPL top filter with ND32 CPL facing outwards, and no base filter installed. The expected increase in yellow saturation, decrease in blue saturation is clear, and a more or less even shift of the other hues. White, which is indicated by the central dot is not significantly shifted off center.
The mist base filter alone shows the desaturating effect of a diffusion filter, affecting all hues almost equally, with the exception of blue, which is desaturated more than the others. There are small hue shifts in red, magenta and blue also. White, which is indicated by the central dot is shifted a bit more off center towards yellow.
Mist (Diffusion) 2-5 Stop VND Filter
The Mist 2-5 stop VND comprises the Mist VND base filter plus the 2-5 Stop/CPL top filter, with 2-5 Stop facing outward. This combination seems to produce some interesting color shifts. The increased yellow saturation from the 2-5 Stop top filter is just about cancelled out by the desaturating effect of the Mist VND base, but all the other hues are desaturated and shifted significantly. White, is shifted significantly off center towards yellow.
Mist (Diffusion) 6-9 Stop VND Filter
The Mist 6-9 stop VND comprises the Mist VND base filter plus the 6-9 Stop/ND32 CPL top filter, with 6-9 Stop facing outward. This combination produces the largest color shift of all, with significant shifts saturation and in hue of all the color chips except yellow. White, is shifted significantly off center towards yellow.
All things considered, this is a great filter system for anyone looking to get a lot of functionality out of minimal gear. I won’t hesitate to take this with me on most shoots, and especially when travelling and keeping my bag lightweight. I will however, always take my color chart with me too.
All variable ND filters introduce color shifts that need to be corrected. The commonly employed, simple color temperature correction is not able to correct the shifts to specific wavelengths of light. The only way to accurately correct your images when using any variable ND filter is to shoot a reference chart and correct hue and saturation in post for each color chip.
The Freewell Versatile Magnetic VND filter is not especially bad, I would place it in the middle average of mid-priced VND filters. The color shifts are easily correctable if you shoot a reference chart.
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