long exposure photography Photography Articles

A Quick Primer on How Variable ND Filters Work

what is a variable nd filter

Not all that long ago, I used a complete ND filter kit - I had five rectangular ND filters and a filter holder to carry around.

I’m not knocking the performance of that filter kit because it was great. But eventually I got tired of having all that stuff in my camera bag. I also got tired of constantly attaching the filter holder, unattaching it, inserting filters, swapping filters out, and so forth.

That’s when I decided a variable ND filter was the way to go.

In this article, learn what a variable ND filter is and how variable ND filters work. 

What is a Variable ND Filter?

best variable nd filter

As you might have surmised already, a variable ND filter is like a bunch of ND filters in one, thus the “variable” part of its name. Like traditional ND filters, variable ND filters block out different levels of light. 

Rather than having a big filter kit with various filters, each with a different degree of filtering power, a variable ND filter simply screws onto the end of your lens.

In that regard, it’s much more user-friendly, both from the standpoint of having less stuff in your bag and not having to fool around with multiple filters every time you want to take a shot.

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How Variable ND Filters Work 

why variable nd filters are better than fixed nd filter

The premise of how variable ND filters work is quite straightforward.

It’s able to block out light because of the manner in which it’s constructed - there’s two layers of polarized glass positioned opposite one another. The inner layer of glass is what attaches to the lens, and is fixed in place. The outer layer of glass is housed in a ring that allows the filter to rotate.


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Since it’s fixed in position, the inner layer of glass reduces light on a single plane. The outer layer, however, can reduce light to a varying degree because it can rotate. That is, the further the outer layer is rotated, the more light-reducing power it has. 

In other words, as the outer layer of glass approaches a 90-degree angle to the inner layer of glass, the maximum light-reducing power is achieved.

Why Variable ND Filters are Beneficial

how to use a variable nd filter

As noted above, variable ND filters are simply easier to use than a traditional ND filter setup.

Rather than inserting individual ND filters in to a housing, you can simply rotate the outermost layer of glass of a variable ND filter to get the desired effect.

What’s nice about this is that you can fine-tune the filtering power to a precise degree to get the exact outcome you want. That is, where a fixed ND filter has a set amount of light-stopping power, a variable ND filter gives you a range from which to choose, usually from about 1-stop to 8-stops.

As you can see above, the lens housing has markings that indicate which way to turn the filter to increase or decrease its effects.

Another benefit of good variable ND filters is that they don’t display the dreaded X-pattern that you often find in bargain variable ND filters. See how this can be accomplished in the video above by Kenko Global

This X-pattern occurs when you push the filter too far to its minimum or maximum range, at which point the two filter elements begin to interfere with one another. This pattern can also emerge on very long exposure.

Photographers like variable ND filters because they make composing images much easier than standard ND filters do. By that, I mean that you can rotate the filter to a minimal degree of filtration, compose the shot, and then adjust the filtration to the desired level.

why variable nd filters are beneficial

photo by RobChristiaans via iStock 

This is particularly handy when you needa lotof filtering power, like 10 stops, to create dreamy scenes like the one above. If you use a fixed ND filter, all that light-stopping power makes it virtually impossible to see the scene through the viewfinder. Granted, you can compose the shot ahead of time and then add a fixed filter, but simply being able to turn a variable ND filter to adjust it is much more convenient.

Of course, like fixed ND filters, variable ND filters offer the benefit of allowing you to slow down the shutter speed to blur motion or open up the aperture to reduce the depth of field.

These are important factors that can be used for all kinds of photography, from portraits to landscapes, street photography to action photography.

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Invest in a Good Variable ND Filter 

benefits of variable nd filters

As noted above, good variable ND filters minimize the X-pattern you find in cheaper versions. With improved optics and build quality, higher-end variable ND filters will also last you a lot longer than some cheap thing you pick up on Amazon.

I use the Kenko Variable NDX filter, and it has been a joy, to say the least.

Like any good filter, it offers hyper-neutral results with no color casting. That’s thanks in large part to its Japanense Asahi Optical Glass and match polarization foils.

how variable nd filters work

 photo by miroslav_1 via iStock

I also like the fact that there’s so much variability with this filter - from 1.5 stops up to 10 stops. From slight motion blur in a waterfall to ethereal landscapes in which the rolling tide is rendered beautifully smooth, this filter can do it all!

And since it has such a wide range of filtering power, there’s no need to stack filters, and that means less vignetting for a cleaner, crisper shot from edge to edge.

Give the Kenko Variable NDX filter a try, and you’ll see that it is well worth the investment!


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A Step-by-Step Guideline for Long Exposure Landscape Photography

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When you see a long exposure image like the one above, what first comes to mind is probably how beautiful it is. Unlike a traditional image, a long exposure is much more dynamic; rather than capturing a split second in time, it gives us a view of what a landscape looks like over seconds, minutes, or even hours.

After pondering the image’s beauty, you might have thoughts about how complicated it must be to create images like that. After all, what you see in the landscape as you’re creating the image isn’t what you end up with in the final photograph. That must be hard to do, right?

Not so! To think that long exposure photos are overly difficult or time-consuming is a misnomer. All it really takes is good planning, practice, patience, and the right gear - things that any good photograph requires. See what I mean in my video above!

Let’s review the essential steps you need to take to create compelling long exposure images of landscapes.

Step 1: It’s All About Location

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The first step in creating a gorgeous long exposure image is choosing a landscape that is conducive to this kind of photography. Long exposures are ideal for conveying movement, so whatever landscape you choose, ensure that there is something in the scene that will indicate the passage of time - a river, a waterfall, waves crashing on the beach, or passing clouds come immediately to mind as ideal subjects.

Once you’ve identified a location, think about ways that you can incorporate static objects into the shot to give the moving element a greater feeling of motion. Boulders in a stream, for example, create a nice juxtaposition with the movement of the water as it rushes by. A building set in front of a sky full of blurred clouds works nicely as well.

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Step 2: Consider Your Timing

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Because you’ll be working with long shutter speeds, lighting is a crucial consideration for long exposures. Shooting at dawn or dusk, before the sun rises and after it sets, allows you to extend your shutter speeds to highlight the movement discussed above, but do so without overexposing the image.

Alternatively, you can use a neutral density filter to make daytime long exposures a possibility. A neutral density filter blocks out light such that you can utilize a longer shutter speed. Neutral density filters come in a variety of strengths, from those that extend the shutter speed to a few seconds to those that make hours-long shutter speeds a possibility. As a general rule of thumb, a 10-stop neutral density filter is a good starting point for daytime long exposures.

When thinking about timing, you also need to consider the best time of day or year to capture the photo you have in mind. For example, a beach shot of the waves coming in would be best at high tide, so you’d need to know the tide schedule to capitalize on that. Springtime is when most thunderstorms occur in many areas, so to get a long exposure of a passing storm, you’d need to plan to be most active during that time of year.

Step 3: Get Geared Up

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Aside from a neutral density filter, you’ll need a few more pieces of gear that are essential to a successful long exposure image:

  • A camera body with the capability of long shutter speeds, including bulb mode. A DSLR or mirrorless body is a good choice.

  • A wide-angle lens, which allows you to capture more of the scene, and thus more movement as well. This isn’t to say that you can’t create long exposures with longer lenses, but wide-angles are simply preferred.

  • A sturdy tripod that will remain absolutely still throughout the exposure. A tripod with a center column hook is a great idea because it allows you to hang a bag to add weight, thereby making the tripod more stable.

  • A remote shutter release is essential because it allows you to trip the shutter without actually touching the camera. This reduces the chance of vibrations, which can ruin a long exposure photo.

Quick tip: Remove your camera strap from the camera body before mounting it to the tripod. The camera strap can catch any breeze that’s present and cause the camera to shake during the exposure.

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Step 4: Dial in the Settings

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This is the most complicated aspect of creating a long exposure because every situation will be different. That being said, because the shutter speed is prolonged, no matter what the situation, you’ll need to adjust the aperture and ISO setting to ensure you get a well-exposed image.

Minimize ISO

Generally speaking, this means using the lowest possible ISO setting (which is usually 100 or 200). Remember that ISO determines the sensitivity of the camera sensor to light, so using the lowest value means that the sensor is minimally sensitive. Additionally, by using the lowest ISO you can will minimize digital noise in the shot, which looks like grain in a photo taken with film. The less noise there is, the higher the image quality will be.

Use the Smallest Aperture Without Sacrificing Sharpness

You’ll need to step down the aperture as well. However, don’t use the lens’ smallest aperture. As you approach a lens’ smallest aperture opening, diffraction, which causes blurriness around the edges of the frame, starts to occur. Instead, opt to shoot as near the lens’ sweet spot (it’s sharpest aperture value) as you can. This is usually in the f/8 to f/11 range, which is plenty to give you a nice depth of field while maintaining sharpness throughout the photo.

Manage Movement With Shutter Speed

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The movement indicated in the long exposures you create depends on the shutter speed. For greater indicated movement, use a longer shutter speed. For less movement, like in the image above, dial in a shorter shutter speed.

Of course, the shutter speed you use will depend on the subject as well. Very fast-moving subjects, like passing cars on a highway, might be blurred with just a one-second exposure. Conversely, a slow-moving stream might require several seconds just to get a little bit of movement.

The point here is that the shutter speed you use will require a good bit of experimentation. Each subject will be different, and your creative vision will change as well. Just be prepared to try a wide range of shutter speeds before you begin to get an idea of what will work best for the shot.

Shoot in RAW

Where a JPEG is a lossy format - that is, some of the data recorded from the sensor is thrown out to create a smaller file size - a RAW file maintains all the information collected by the camera’s sensor. By shooting in RAW, you’re doing yourself all kinds of favors when it comes to post-processing because you’ll have much more data to work with. What’s more, you can make non-destructive edits to RAW files, so no matter what you do in terms of processing, the original RAW file will be unchanged.

Better still, RAW files open up many more possibilities for processing. You can adjust white balance, levels, curves, saturation, brightness, and correct for lens distortion, among other things, right from the RAW editor.

Step 5: Mind the Composition

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Once you arrive at your selected location, take a few moments before setting up your gear to think about the composition of the shot. This involves a number of considerations:

  • Where is the movement occurring? If you’re photographing water, take a lower shooting position such that you can incorporate as much water into the shot as possible. If you’re photographing the clouds, adjust your shooting angle such that you can capitalize on the sky.

  • What elements of interest can you include? As mentioned above, adding static elements to the shot will help enhance the feeling of movement. Look for natural or manmade objects that you can incorporate into the scene to add interest, like the dock and the boat in the image above.

  • Consider the foreground. Foreground interest will help draw the viewer’s eye into the shot. Leading lines, like the dock in the image above, are especially powerful foreground elements.

Quick tip: When composing the shot, think about how you’d compose it if it were a traditional, static image. Meaning, watch your framing to ensure there aren’t any elements like tree limbs or street signs protruding into the shot. Look at the background to ensure it isn’t distracting. Examine how any shadows fall across the scene and if they enhance or detract from the shot as well.

But, also consider how movement will occur as the shutter is open. In that regard, you have to anticipate where the object will be when the exposure ends. For example, if clouds are your chosen subject, don’t just frame the shot based upon where the clouds are at the outset - think about how far the clouds might move over the course of the exposure and frame up the shot accordingly.

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Step 6: Process the Image

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Though you should strive to get everything right in-camera, a little post-processing can go a long way to enhance the look and feel of your long exposure landscape images. Consider enhancing colors by boosting saturation or vibrancy. Adjust the levels and curves to create an image with a more robust dynamic range. If you find areas of the shot are too bright or too dark, try your hand at dodging and burning to create a more well-exposed image throughout. A little sharpening might be in order as well.

Ultimately, however, what you do in post-processing will be a personal preference that is as much your own creative spin on photography as it is to compose the shot in the field. Make the adjustments that you feel are necessary and create the image that you want to create. By following the steps outlined here, you’ll be well on your way to making long exposure landscape photos that match your creative vision, whatever it might be.

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