Quick Tip: Three Handy Uses for Neutral Density Filters
If you haven't had experience using a neutral density filter, you might wonder about the usefulness of a dark piece of glass that attaches to the front of your lens. Neutral density filters are a unique accessory that may seem strange at first sight. However, in today's quick tip, we'll take a look at three photographic situations where using a neutral density filter can change your photographs for the better.
What is a neutral density filter?
The first time I saw a neutral density filter, I was having a hard time understanding their usefulness. I had tried to get fast lenses with wide apertures and cameras with good high ISO performance, so my gear was all about making the use of the least light available.
Neutral density filters, or ND filters, are designed to reduce the amount of light that reaches the camera's sensor.
This is a neutral density, or ND filter.
ND filters, which attach to the front of your lens, are labeled by the amount of light they reduce, in 1/3rd steps. For instance, an 0.3 ND filter reduces one stop of light. That's equivalent to reducing the ISO from 200 to 100, or the shutter speed from 1/500th of a second to 1/250th of a second.
When can I use a neutral density filter?
Although it may not be obvious when an ND filter can be handy, let's look at three situations where they are certainly game changers.
Long Exposure Photos
If you are interested in shooting very long exposure photographs, ND filters are often the best way to achieve these exposures. Even if our settings are set to allow the least possible amount of light through, it's sometimes not enough.
Often times, photographers shooting long exposure photos want the absolute longest exposures possible. Let's say that you're in a situation when a one minute exposure is allowing too much light through. That 60 second exposure is blurring the action just as we want it, but an overexposed photo is far from our desired outcome.
In this situation, attaching an ND filter helps us keep our 60 second exposure and cuts the light reaching the sensor, balancing our exposure nicely.
In this long exposure photo by Flickr user Steve-H, the photographer used an ND filter to achieve a long exposure even in sunlight.
Shallow Depth of Field Portraits With Flash
One issue about shooting photos with flash is a technical limitation known as the flash sync speed. This is the shutter speed that a camera and flash unit can stay in sync. Usually, this sync speed is somewhere in the neighborhood of 1/250th of a second. To reliably fire the flash in sync with the shutter, your shutter speed must be at this speed or slower.
On bright sunny days, we may want to shoot a portrait outdoors that uses flash. We've set our ISO low, and set our shutter speed to the maximum sync speed. However, there is one setting we've had an issue with: aperture. We want to keep our aperture wide at something like f/2 in order to preserve shallow depth of field. The issue here is that this aperture is allowing too much light through, and thus we have an overexposed photo.
Again, enter the ND filter. We can balance our exposure by using the filter to reduce the amount of light entering the equation. We've set our ISO as low as possible, our shutter speed as fast as possible, and our ISO at a desirable setting. Then, we threw the ND filter into the equation and got it all in balance.
Keep in mind that your flash will need to be at a high power in order to balance with the other settings. You'll may even need to switch your flash to manual in order to get the best results.
This photo illustrates perfectly the concept of using a neutral density filter with flash; the photo is designed to preserve shallow depth of field and still use flash on a sunny day. Photo by Ernst Vikne
Landscapes: The Graduated Neutral Density
Finally, a special type of neutral density filter that has been the staple landscape photographers' work can be used to perfectly balance nature scenes. Graduated neutral density filters, or GND filters, are used to balance the varying exposure areas within a photo.
The classic example of this is balancing the exposure of the sky with the foreground of the photo. In most landscapes, the sky is going to be the brightest portion of the image, while the foreground will be darker by comparison. Often times, we struggle to replicate the "blueness" of the sky because it's overexposed. Being overexposed makes the sky appear a light blue, or even white, and we lose the effect we are looking for.
A graduated neutral density filter is partially shaded to darken some parts of the photo, while leaving the rest untouched.
The GND filter helps to fix this scenario. Looking at a GND filter, you'll notice that the top of it is darker than the rest. Those areas look to control the sky, for example, and leave the exposure of the foreground untouched.
This photo by Flickr user Kain Kalju is a great visualization of the effects of graduated neutral density filters. We see the effect that the shaded part of the region has on the sky, while the clear part doesn't impact the foreground of the image.
Neutral density filters are unique tools that are useful beyond what you may first believe. These three scenarios above are great uses for ND filters. Consider using one to adjust the photographic exposure triangle to your liking.