The best variable ND filters are an ideal companion for videographers, filmmakers and photographers alike. Giving you incredible flexibility for controlling the amount of light that enters a lens, variable neutral density filters can be adjusted to different levels of opacity, meaning you can block a lot of light, or relatively little, all with the same filter.
A variable ND filter allows photographers can slow down their shutter speed to create amazing long exposure effects. These include creating milky seas and skies, erasing moving people from an urban scene and creating dramatic light trails.
This can be done with the best neutral density filters too, and will give you better image quality. However, these filters aren't adjustable. If you've got a 10-stop filter mounted to your lens, and you want only 8 stops of light reduction, you've no choice but to change filters (assuming you have an 8-stop one too), which takes time and necessitates carrying around a lot of fragile glass.
Variable ND filters keep your kit light, and reduce your chances of missing the shot. Variable NDs also have plenty of applications for videographers, who have fewer options for varying and controlling exposure sine they're usually using a fixed shutter speed.
1: A variable ND filter may present its density range as ‘ND2-ND400’. At ND2 you’ll get a one-stop reduction in light transfer, and at the ND400 position there’ll be an eight-stop reduction.
2: At maximum density you’ll see a cross effect that often creates an uneven exposure.
3: Variable NDs can create unwanted effects with ultra-wide lenses, so longer focal lengths are best.
4: Some filters have coatings that help improve light transmission and reduce reflections.
A variable neutral density filter is essentially two polarizers fixed together to form one screw-on filter. When the user rotates these two filters against each other, the elements restrict the amount of light that's able to pass through.
Variable ND filters re also referred to as 'faders', partly because many of them will produce a slight color cast (another reason why many photographers prefer traditional neutral density filters). It's also worth noting that if a variable ND filter is rotated too far, they will tend to produce a darkened X effect, which will appear on your image. This is often referred to as 'crossfade'. It's pretty much ubiquitous on ND filters, so is just something you need to watch for.
As long as you know what you're getting into, variable ND filters can be a tremendously useful tool. Here are, for our money, the best variable ND filters you can buy right now.
There aren't a lot of genuine surprises in the world of photographic filters, but H&Y's Revoring system is something else. This clever device is two filters in one – both a polariser and a variable ND filter, and what's more, its spring-loaded attachment mechanism means it can adapt to a huge range of filter sizes.
In use, the two filters rotate independently via small metal lugs. You rotate the rear filter and front filter together for the polarising effect, and turn the front filter relatively to the rear to apply the variable ND effect. If that sounds complicated, well, it is. But, as we discovered in our review, once you do get used to it, the system works extremely well. The top-tier quality of the glass in the filter helps too, ensuring top-notch image quality.
Not everyone will find it useful having a polariser and variable ND in the same place. But for those who do, the H&Y Revoring is a no-brainer.
With its ND2-ND400 density range, Marumi’s filter enables between one and eight stops of light reduction. Inevitably, you’ll need to stop well short of the max if you want a completely balanced exposure; we found three stops to be the maximum density with no sign of brightness inconsistency. There’s only a hint of a warm tone when shooting a neutral test surface, and no visible colour casts in real-world shooting.
Marumi’s build quality is more than acceptable for the money, with a fairly smooth rotation that has a good amount of resistance. There’s also a ridged texture around the fixed section, so it’s easy to grip while fitting and unmounting. The only minor omission is a lack of hard stops to mark each end of the density spectrum.
No mention is given of advanced coatings, but the filter does shed water quite well, and fingerprints rarely stick.
Syrp likes to do things a bit differently, and even its humble variable ND filter gets a unique treatment. It comes packaged in a classy cylindrical cardboard outer carton; the filter gets a round, leather-wrapped zippered storage pouch.
Instead of the usual range of multiple filter sizes, there are only two core versions of the Syrp filter: a 67mm and an 82mm. The former comes in the Small kit option, which includes adapter rings to mount the filter to 58mm and 52mm lenses, while the 82mm Large kit contains 77mm and 72mm adapters.
Syrp’s fancy packaging isn’t a case of style over substance, though. We found the filter neutrality to be exceptional, with no color casts evident.
The ND2-ND400 range also contains an impressive four-stop band with no visible exposure inconsistency. Factor in the water and dirt-resistant front coating, and you’ve got one fabulous filter.
This is one pricey screw-in filter – but maker Schneider Optics claims it’s a cut above the competition thanks to a Multi Resistant Coating. Where an uncoated filter can reflect around 4% of light, this one only reflects 0.5%, while also minimizing ghosting and reflections, and repelling water droplets.
The filter is 9mm deep, not including the thread, with knurling around the fixed ring that makes it a doddle to fit and unscrew. The rotating front ring has hard stops to mark the minimum and maximum filter densities, but markings in-between don’t correspond to f-stop light reduction amounts. Rotation is smooth, with pleasing resistance.
The filter is said to provide between one and five stops of light reduction, which we found to be accurate, but expect uneven light transfer beyond around three stops of reduction.
Filter neutrality is good – image quality is exceptional, with little or no color cast evident, and good tone and contrast throughout the image.
Hama’s slimline variable ND filter is well made for the price, with a smooth rotation between the two elements and just enough friction to hold its position when set.
A slight textured edge to the front element makes adjustment easy, and there are clear markings between the minimum and maximum points.
At the minimum setting the filter enables you to lengthen the exposure by one stop and influences color with a slight coolness.
We found that increasing the intensity to the maximum marked setting produces a heavy black X, but pull back a little and you can extend exposure times by almost eight stops (although images do need retouching to remove the color cast).
A setting of around five stops gives the cleanest results.
Hama claims the filter is coated, but gives little detail of the benefits. They certainly don’t include moisture or fingerprint resistance, as the filter attracts both. It’s also a pity you can’t get the Vario in an 82mm diameter.
Arriving in a quality plastic case, the Cokin ND X is an extremely slim, lightweight screw-on filter with a premium feel.
The front element rotates smoothly, with a good amount of friction holding the filter precisely where you want it to be set.
At the minimum setting you can expect an exposure reduction of one stop, and the filter to add just a touch of warmth.
Rotating to the maximum marker (eight stops) creates a dark X, but ease off and you can extend your exposure times by six stops (taking a 1/60 sec exposure up to a full second) and still get usable images.
Red and blue color casts do affect the image, but overall contrast and tone are good and the casts are easily corrected. In our tests, we found that four stops provides the optimum setting.
The Kenko is a relatively deep filter, but it has the very useful addition of an optional knob that can be screwed in to assist with the easy rotation of the front element. This is a nice design feature, particularly for video, but the rotation itself isn’t quite as smooth as with some of the other filters on test. However, the overall build quality is good.
In use the Kenko filter provides a stop of exposure extension at the minimum setting, and a blue X across the image at the maximum marked setting.
It’s possible to extend exposure times by up to around eight stops and get usable images, and color rendition, tone and contrast are all pretty good. However, the extra depth does make this filter prone to the effects of flare.
How we test filters
When we test filters, we look at both optical performance and general build quality – how robust the filter feels, how easy it is to use and how securely it attaches to the lens. We use a combination of real-world and lens testing to inform our comments in reviews and buying guides. For filters, we test light transmission levels, colour neutrality (i.e. if the filter introduces a cool or warm cast) and the impact a filter has on image quality. We also look at any specific known issues with different kinds of filters – so for variable NDs, we look out for the infamous 'crossfade' effect, which is the X-shaped pattern these filters are known to produce.
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