Variable ND filters are an essential accessory for videographers. Variable neutral density filter (variable NDs) are adjustable filters allow you to regulate the amount of late entering the lens.
With video, you are usually shooting at a fixed shutter speed, so an ND filter becomes essential if you are to be able to freely adjust the aperture – and therefore control depth of field. A variable ND filter gives you this flexibility. You choose the aperture and shutter speed you want, and then adjust the ISO and the filter to get the right exposure for your shot.
For photographers, a variable ND filter can be used to allow you to get longer shutter speeds to increase motion blur. In urban settings, moving people and vehicles can be blurred or even made to disappear. These filters also appeal to portrait photographers, as they enable them to set wide apertures (and so blur our backgrounds) even in very bright conditions.
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.
Traditional neutral density filters for photographers have a fixed effect, reducing the amount of light reaching the sensor by a fixed amount. But a variable ND filter – these are basically two polarizers fixed together to form one screw-on filter. As they’re rotated, the elements restrict the amount of light that is able to pass through them, and therefore extend the exposure time.
Despite the ND title, many are simply known as faders, as they do produce slight color casts (so aren’t strictly ‘neutral’), and if they’re rotated too far, almost all will reveal a darkened X, which will appear on your image.
Here we take a look at six variable ND filters and discuss how they perform.
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.
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