Variable ND Filters: What are you Paying For?

Independent filmmakers working with DSLRs and mirrorless cameras should all have one critical accessory in the bag: a variable neutral density filter. This nifty little tool can change the way you shoot by allowing you to follow the 180-degree shutter rule more easily, or simply use wider apertures for shallow depth of field. It is also quite affordable. However, if you go shopping you may notice there is a dramatic range of prices for variable NDs, so we brought some samples out to see how radically they differ.

To avoid going overboard, we chose one filter to be representative of each price range, one on the ultra-affordable end and another in the medium-high range. We will refer to the affordable option as “Filter A” and the high-end sample as “Filter B.” Also, all the images were edited with the same settings to keep conditions consistent.

Build Quality

The first indication of the difference in price is obvious when you open the package. Filter B rotated more smoothly and screws on cleanly to the lens, whereas Filter A had a little bit of a gritty feel in both aspects. While in many cases, this isn’t the end of the world, it makes a difference if this is a tool you will be relying on for much of your shooting. I will admit, it is the first place I would start cutting corners if were looking to save some money.

From a usability standpoint, the pricier Filter B also had a larger area with which to adjust density, while keeping a relatively slim form that shouldn’t interfere with your images. Filter A had such a small grip for adjustments that it was tough to make quick adjustments because I had to be mindful of where I positioned my fingers to avoid leaving fingerprints on the filter. Overall, build quality was an easy winner in the upper-end Filter B.

Density

Now let us look at image quality. To pull off this test, I went out to capture two city scenes, one at a wide 24mm and another at 135mm. This let us see how each filter reacted to working at different focal lengths, especially since wide-angle lenses tend to push the limits of these adjustable filters. Part of the selection process involved making sure we had filters that offered the same range; in this case it was 2-8 stops.

Filter A came close to the stated range, though, surprisingly, Filter B seemed to be about a stop lighter on both ends, which may have been a way to maintain overall quality. The reason for this is extremely clear once you look at the darkest end of Filter A, where there is an extremely noticeable X effect when it’s on the 24mm lens. Filter B also has a slight X effect occurring at its densest setting, though it is much less noticeable, and the color shift at the darkest points is nowhere near as dramatic. So, while the affordable Filter A achieved a greater and more true density consistent with the stated figures, in practice you wouldn’t be able to use it at these settings.

Sharpness

When you add anything to the lens, even seemingly clear glass, you will always lose something when it comes to ideal image quality. With variable ND filters, this can be even more pronounced because it features two pieces of glass. At lower densities, the ND filters both performed admirably, with only a minor loss in details compared to the no-filter image. Once we kicked it up to the other end, things became dramatically worse. Filter B was noticeably better that Filter A in this regard—the greater the density, the more detail was lost. This was apparent even at mid-range settings like the examples below. So, if sharpness is critical, go for something like Filter B.

Color

One thing you may have noticed already is that the filters tend to impart a distinct color cast to images. I noticed that at the wider end, they tended to skew slightly yellow and, at the darkest side, they went blueish. I want to look at the telephoto shots because that is where the difference is most obvious.

Here it is clear that the pricier Filter B is going to be a better choice, since it is a lot closer to the original, though it is still off. Filter A appears to take on both a blue and magenta tint, while Filter B appears to be more blue with a slight green tint. This is arguably one of the most important aspects to compare—if you are filtering out certain colors, you may never be able to get the proper colors during editing because they were lost during capture. If you intend to use both the very dark and very light ends of the scale, then it would probably be wise to look at more advanced offerings.

Conclusion

So, can you get away with a less expensive filter? This was just a quick overview but the answer is: absolutely, yes—once you understand the specific limitations and oddities of the model you purchase. However, going up in price will generally result in improved overall image quality and less time in the editing stage. The more expensive filter showed not only better build quality and usability but, in some cases, vastly improved IQ. This comparison does remind me a bit of lenses, where the difference in price between an f/1.8 and an f/1.4 lens can be vast, even with the difference being less than a stop. It will be up to you to determine whether the added performance is worth it.

Are you a fan of variable ND filters? Are there any you would recommend? Let us know in the Comments section, below!