Understanding Variable ND Filters & How to Select the Best One

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Are you struggling to understand variable ND filters and how to select the best variable ND filter?

Then you’ve come to the right place.

Because in this article, I’m going to tell you everything you need to know about these filters and their effects.

Now, variable ND filters may seem complicated, but they don’t have to be. The concept is fairly simple.

With a normal ND filter, you can minimize the amount of light that reaches your camera sensor (like putting sunglasses over your lens).

But with a variable ND filter, you get to decide how strong you want the darkening effect to be. You can adjust the filter to give you an ultra-strong effect, or you turn the filter to achieve a relatively weak effect.

Let’s take a closer look:

What is a Variable ND Filter?

A variable ND filter is designed to reduce the light hitting your camera sensor without altering the color. By turning the variable ND filter, you can alter its effects–giving you the option of working with a weak ND filter or a strong ND filter, depending on your needs.

How Variable ND Filters Work

While there are a number of ways to create variable ND filters, the simplest involves placing two polarizing filters together.

If you arrange the polarizers so that they work in opposition to one another, you don’t get a polarization effect. Instead, the polarizers simply block out light–with the strength of the light-blocking effect dependent upon the way the polarizers are arranged.

As you turn the outer polarizer, the light-blocking effect increases or decreases its strength.

This is ideal for photographers looking for a flexible way to reduce light levels. For instance, if you’re photographing running water in the middle of the day, you’ll find that a variable ND filter will let you reduce your shutter speed significantly, so that you can create a beautiful blur effect.

Then, as the light changes, you can increase or decrease the ND filter effect, in order to maintain the same shutter speed. You can also use a variable ND filter to use several different shutter speeds for the same shot (even with a constant aperture and ISO).

Do Variable ND Filters Produce Polarizing Effects?

No, variable ND filters do not produce a polarizing effect.

While variable ND filters are constructed using polarizers, they do not actually work as polarizers.

If you need a polarization effect, you must use a true polarizing filter.

But if you want to simply reduce light levels, then an ND filter is the way to go.

Variable ND Filters vs Fixed

While variable ND filters are one way to reduce light transmission, you also have another option:

Fixed ND filters, which also mount in front of your lens, and offer a fixed amount of light reduction.

Now, fixed ND filters are far less flexible than variable ND filters. While a variable ND filter allows you to adjust the amount of light hitting the sensor, a fixed ND filter stays constant. This means that you will need to carry multiple fixed ND filters if you want to match the effects of a variable ND filter.

However, fixed ND filters come with a big benefit:

Quality.

Fixed ND filters are, on average, higher quality than their variable ND counterparts. They produce less vignetting, give sharper images, and have no cross-pattern effect. They’re also a lot cheaper.

Really, it’s a lot like the question of prime versus zoom lenses:

Do you want the quality of primes, or the convenience of zooms?

It all depends on your needs and what you’re willing to sacrifice. If convenience is of key importance to you, then go with a variable ND filter. But if you require the absolute best quality, then a fixed ND filter is the better option.

Do Variable ND Filters Affect Image Quality?

Technically speaking, all filters affect image quality–though some filter types are much worse than others.

Related: Best Lens Filter Brands

Variable ND filters do cause a number of optical problems you have to watch out for, especially if you purchase poor-quality glass.

Vignetting

First, some variable ND filters cause vignetting. This can be taken care of pretty easily in post-processing, but if you like to minimize your time spent behind a computer, you’ll want to purchase the highest-quality variable ND filter you can afford.

Color Shifts

Second, lower-quality variable ND filters cause color shifts. This manifests as a tint across the entire image.

Like vignetting, this is an effect that you can remove in post-processing, so it may be something you’re willing to tolerate.

Cross-Pattern

Third, all variable ND filters cause an unpleasant cross-pattern effect at full strength.

A large ‘X’ appears across the center of the image, and is extremely difficult to remove in post-processing.

In fact, this is one of the biggest drawbacks to variable ND filters, and you cannot prevent it by purchasing a higher-quality filter. So you always have to be on the lookout for the cross-pattern effect when shooting.

General Softness

High-quality filters won’t cause much, if any, softness.

But if you purchase low-quality filters, the kind that cost just ten or twenty dollars, you’re going to end up with very soft images.

That’s why I recommend purchasing the best filter you can afford.

Best Variable ND Filter Models

Now let’s take a look at the best variable ND filters you can buy, no matter your budget:

01. Heliopan Variable ND

Heliopan 67mm Variable Gray Neutral Density Filter (706790) with specialty Schott glass in floating brass ring
Heliopan Variable Gray Neutral Density Filter

Heliopan is known for their high-quality filters, and this variable ND option is no exception. You get a 1-6 stop variable ND effect, allowing you significant flexibility in choosing your shutter speed. The filter itself uses high quality materials: brass, for an extra-durable ring, and Schott glass, for the highest-possible image quality. Unfortunately, the Heliopan Variable ND isn’t cheap–but if you’re looking for the absolute best quality, this filter is the way to go.

02. Tiffen Variable Neutral Density Filter

Tiffen 77mm Variable Neutral Density Filter 77VND for Camera lenses,black
Tiffen Variable Neutral Density Filter

While the Tiffen Variable ND filter comes in at one-third the cost of the Heliopan Variable ND, its performance is surprisingly strong. The Tiffen Variable ND features top-notch image quality with limited loss of sharpness, as well as solid construction for long-term use. You also get a broader ND effect compared to the Heliopan, from 2 to 8 stops light reduction. The Tiffen Variable ND filter is a great choice for anyone looking to spend less but achieve an image quality that rivals more expensive options.

03. B+W XS-Pro Digital ND Vario MRC Nano

B+W 77mm XS-Pro Digital Vario ND with Multi-Resistant Nano Coating
B+W XS-Pro Digital Vario ND with Multi-Resistant Nano Coating

The B+W XS-Pro Digital ND Vario MRC Nano filter is neither the cheapest nor the most expensive filter on this list, but it delivers in all the key ways. The filter features excellent ergonomics, allowing you to smoothly move throughout the range of ND effects. You get between 1-5 stops of light reduction with minimal vignetting and strong image quality; you also get a high-quality brass ring to increase durability.

04. NiSi Variable ND Filter

NiSi NIR-VND-77 Variable ND 1.5-5 Stop Filter, 77mm from Ikan, Black
NiSi NIR-VND Variable ND 1.5-5 Stop Filter

The Nisi Variable ND filter isn’t the most popular option on the market, but it’s a solid one, combining a reasonable price with good performance. The filter offers a 1.5 to 5 stop light-reduction effect, and uses nano-coated glass to minimize flare. The NiSi Variable ND filter also includes an easy-to-use design, with dots indicating the strength of the ND effect as you rotate the filter. While the NiSi Variable ND filter doesn’t exactly come cheap, it’s what you pay for a high-quality ND filter like this one.

05. PolarPro Variable ND Peter McKinnon Edition

PolarPro 82mm Variable ND Filter (2 to 5 Stop) - Peter McKinnon Edition
PolarPro 82mm Variable ND Filter (2 to 5 Stop) - Peter McKinnon Edition

This PolarPro Variable ND comes at a premium price, but offers quite a lot for the serious photographer or videographer. You get a suave design, including an aluminum ring (painted gold around the side). You also get high-quality quartz glass for a minimal vignetting effect. Aside from its price, the main drawback of the PolarPro Variable ND filter is its range: The standard filter offers only 2-5 stops of light reduction–though you do have the option to purchase the (more expensive) 6-9 stop version.

Conclusion

Now that you’ve finished this article, you should know all about variable ND filters:

What they are.

How they work.

And which one is best for your needs.

Variable ND filters are a fantastic way to increase your flexibility in the field, especially for landscape photographers, portrait photographers, and videographers.

So if any of the filters we’ve listed appeal to you, go ahead and grab one!

Amazing images await.

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