In this comprehensive guide, I’ll be answering all of your burning questions about neutral density filters. You’ll learn what ND filters are, how these filters work, which ones to buy, and when to use them. If you’re a photographer looking to push your creative boundaries and improve your photography skills, keep reading all about neutral density filters.
What Does a Neutral Density Filter Do?
Neutral density filters block light from coming into your camera’s lens and on to your camera sensor similar to a pair of sunglasses. This is done without changing the color of the light, which is why they have the word neutral in the name. And don’t fall into the trap of mistakenly saying natural density filter.
When to Use a Neutral Density Filter
There are a few reasons why a photographer may decide to use a neutral density filter. Let’s take a look at a few of them:
First, reducing the amount of light that enters the lens and hits the sensor means the camera’s shutter needs to stay open longer for the image to reach the proper exposure.
The longer the shutter stays open, the more motion blur is achieved from anything that isn’t static—as long as the camera remains still on a tripod or surface.
You’ve probably seen plenty of images throughout your lifetime that have been taken while using a neutral density filter and you didn’t even know it.
One common example are photos of waterfalls where the water looks silky smooth and brighter than it would if you were standing in front of the falls themselves. This is because a longer shutter speed was used to blur the moving water, oftentimes with an ND filter attached to the lens to combat bright daylight.
Another common reason photographers use ND filters is to shoot with a wider aperture in brightly-lit conditions thanks to the light reduction you get from them.
Let’s say you wanted to shoot a portrait of your friend on a sunny afternoon while maintaining a shallow depth of field with plenty of bokeh.
Since it is daytime, you’ll first want your ISO to be as low as possible.
Next you’d want your aperture wide to obtain the shallow depth of field.
This means the only thing left in the exposure triangle to adjust to get a perfect exposure is your shutter speed.
Even with an electronic shutter option on your camera, you’ll probably find your shutter speed won’t be fast enough and your image will be overexposed as too much light enters the lens.
In this case, a neutral density filter comes in very handy to reduce your shutter speed enough to nail your exposure.
Since this portrait effect is hard to replicate without an ND filter, your friends will be impressed with the quality of the results.
Get a Balanced Exposure
A final reason why photographers use ND filters applies mostly to landscape photographers.
Many landscape photographers capture most of their images during the golden or blue hours due to the incredible quality of light. Even as the sun sets, there is a stark contrast between the brightness of the sky and darkness of the ground.
Landscape photographers often use something called a graduated ND filter to improve their photos in-camera to spend less time on post-production.
A graduated ND filter has a gradient starting from clear at one end and dark at the other.
The transition from clear to dark can take place gradually with three standard strengths—soft, medium, or hard. A soft gradient eases into the ND filter, the hard has an immediate switch, and medium lies somewhere between the two.
Landscape photographers can align the gradient on a graduated filter with the horizon to reduce the exposure of a brighter sky while maintaining detail on the ground for a balanced image.
How Many Stops for a Neutral Density Filter
Neutral density filters are measured by the stops of light that are blocked. ND filters come in a variety of stop levels, typically ranging from 1 to 16 stops, with a 16 stop filter blocking 16 stops of light.
You’ll often see other measurements on ND filter packaging or product listings like optical density or ND factors. To get started, I encourage you to focus primarily on the stop levels to make things easier for yourself.
The number of stops highly depends on the type of photo you’re looking to take and the amount of light in the scene.
For landscape shots with blurred water and clouds, you’ll probably want to go for something in the 6 to 10 stop region depending on the time of day.
For shots where you just need to lower your shutter speed slightly, you could get away with using a 2 to 4 stop ND filter.
For extremely long exposure shots lasting hours, you’d be heading into the 11 to 16 stop range.
There are charts available online like this one that help you calculate what shutter speed times match up with various ND filter stops.
What Neutral Density Filter to Buy
Neutral Density Filter Types
If you’re looking to buy a neutral density filter to purchase, you’ll first want to be aware of the different ways they attach to your camera’s lens.
Screw-On ND Filters
The most common type of ND filter is the screw-on. These neutral density filters simply screw onto the filter thread of your lens. You’ll want to check the correct filter thread size in your lens manual or by finding the label on the physical lens when using fixed ND filters.
ND Filter Holder Systems
The second way to attach an ND filter to your lens is by using a holder system. These are usually more expensive, but allow you to quickly swap and/or combine various filters.
These holder systems usually come with adapter rings so you can add them to any lens filter thread size. The filters placed in these systems are not circular like screw-on filters, but resemble glass panes.
You can slide the filter panes into the holder and stack them to block more stops of light or combine with other filter types like a polarizer.
Graduated ND Filters
We’ve already touched on graduated ND filters above, but as a refresher, these ND filters are not a solid neutral density filter. They have a soft, medium, or hard gradient so you can use the filter to target only the brighter parts of your composition.
Variable ND Filters
Variable neutral density filters allow you to adjust the amount of stops. This is typically done by layering two polarizers where the first rotates to allow or restrict the amount of light that can pass through.
Variable ND filters are useful if you are limited on space and time, but often produce some color casting. If you want the best image quality, you’d be better suited using a normal neutral density filter. However, variable ND filters also have the benefit of letting you quickly adjust to changing light—making them a popular option for videographers that are restricted to a specific shutter speed.
Neutral Density Filter Brands
As you may have guessed, there are a lot of filter brands on the market. In many ways, you get what you pay for with lens filters. There are more affordable options, but you may notice vignetting, poor neutrality, or color casting with these filters.
If you’re serious about photography, a good set of filters should last you for years if you take care of them, so the high-end ones are worth the investment.
Here are a few ND filter brands I recommend doing your research on:
Best Neutral Density Filters
It is hard for me to recommend the best neutral density filters without knowing what type you’re after, how many stops you’ll need, and your budget. My best advice is to review highly-rated ND filters on Amazon and use the filters to narrow it down to those that fit your camera, needs, and budget.