When it comes to taking photos and recording videos, there is one filter that you must have in your camera bag. And that is the neutral density filter. In this guide, we will cover all you need to know about the ND filter.
ND Filters Explained
Neutral density filters reduce the amount of light that hits your camera sensor. The filter comes in two types. The first type is a fixed one. This means that it can reduce the amount of light by a certain fixed stop number. For instance, by 2 or 3 stops. A stop refers to a doubling or halving of the amount of light that passes through your lens.
The second type is the variable neutral density filter. As the name suggests, you can choose light reduction within a certain stop range. For instance, it can be from 2 to 8 stops.
Why Do You Need An ND Filter?
We use our neutral density filter primarily in the following situations.
1. Long Exposure Effect
The first scenario is when we take long exposure shots of moving objects. Long exposure means a slow shutter speed in the realm of 1 to 30 seconds. For instance, here is a long exposure image of Elakala waterfall in Blackwater State Park of West Virginia.
There is a swirl of water that Elakala waterfall is famous for. To capture this swirl, a slow shutter speed of at least 5-6 seconds is a must. Also, the long exposure setting would create silky smooth beautiful water effect of the falls as well.
It was daylight at that time. Even if I cranked up my f-stop to the max, I would still not have gotten this shot. The water flow would have been too sharp with droplets visible all over the place. Instead, I used my ND filter with several stops down to produce this shot.
2. Recording Videos with an ND Filter
The second scenario where you need a neutral density filter is when recording a video at bright daylight. We produce and license stock videos for a living. Take a look at our tutorial on how to start with stock videos. The stock video market is growing faster compared to the stock photo market. This is where we are putting our current effort into.
Anyhow, we often find ourselves recording videos at bright daylight. In fact, it is so bright outside that the max f-stop setting still does not produce the correct exposure.
As you may know, recording footage requires a fixed shutter speed. This shutter speed setting must be equal to the double of the frame rate per second. For instance, we record 24-frame per second footage. Thus, our shutter speed must be 1/48.
To compensate for such a low shutter speed, we must increase the f-stop setting. And yet, it is still easy to exceed the min aperture setting and have incorrect exposure at daylight. Again, the neutral density filter comes to the rescue and saves the day for videos.
3. Shallow Depth of Field for Videos
Also, if you are going for a shallow depth of field effect in videos, you need to use a fast aperture of at most f/2.8. At bright daylight, this is only possible with the neutral density filter. Otherwise, you will be forced to use a high f-stop setting. Doing so will render almost everything in focus without blurry background.
ND Filter vs. Max F-Stop Setting
Having the max f-stop setting (typically f/22 or more) is not always optimal. Recall, the smaller the f-stop is, the larger the aperture gets. Aperture refers to how large of an opening your lens has. Thus, larger apertures are associated with a small f-stop setting and vice versa. By increasing the f-stop, you are narrowing the lens’ opening and increase the distance in focus.
Paradoxically, the sharpness of a frame degrades as f-stop setting increases (or as aperture gets smaller). Moreover, a high f-stop setting can make dust specks on your image sensor visible. It is not a problem for a photo, as it takes a second to remove a dust spot. But, it is a completely different matter for a video. It may take much more resources to remove even one dust spot.
How to Choose ND Filter Size?
Lens filters come in different diameters for different lens sizes. The size of a lens is indicated on its body, often at the bottom.
Most of our lenses have 77mm diameters. Thus, we bought a neutral density filter that is also 77mm. But, what if you have a smaller lens? For example, we have a 35mm lens with a 67mm diameter. In this case, there is no need for a second filter. Instead, you can use a step-up ring adapter. Adapters allow you to attach a filter to a lens with a smaller diameter. These adapters are inexpensive at a price of under $10. We use the step-up ring adapters by Altura.
Which ND Filter is Best?
If you are thinking of buying a neutral density filter, we recommend the variable filter. Why? Because you won’t have to buy many neutral density filters for all light situations. We hate carrying around excessive loads in our camera bags. Thus, a variable neutral density filter can be perfect for a minimalist travel photographer.
The variable neutral density filter we use is made by Tiffen. It allows us to have continuous control over the amount of light hitting the lens from 2 (ND 0.6) to 8 (ND 2.4) stops.
Disadvantages of ND Filters
Filters come with their own shortcomings. Not all, but some neutral density filters may give photos a slight color distortion. But, it is relatively easy to correct this color cast through white balance settings in post-processing.
Also, as always, putting more glass in front of your lens will affect the sharpness of the end-product. There is nothing you can do other than to choose a high-quality filter. In our experience, Tiffen ND filters provides an excellent balance between price and quality.
That will be it for this tutorial. I hope you learned something new today and you will look into neutral density filters.