What You Need to Know About Neutral Density Filters

Picture a fantastic scene by the beach. The sun is about the rise while the waves seem to be floating around water. Wouldn’t it be great to capture it in a photograph? However, the camera’s settings might not be enough to duplicate the drama of the view. To preserve or even enhance the image, you will need neutral density filters.

What is a Neutral Density filter?

It is a semi-transparent glass that can either be placed or screwed in front of the lens to obstruct a portion of incoming light but without affecting image contrast and sharpness. It comes in different sizes that fit various camera lens diameters. Although the image will look grey through the viewfinder, the output is impressive. Because of the reduced light, neutral density filters can trigger longer exposure times for dramatic effects such as softer water flow and emphasis on movement.

Aside from long exposure times, neutral density filters also account for a shallower depth of field which contributes to sharper subjects on the foreground and blurred but effective backgrounds. ND filters can also add saturation to the image’s colours for stunning accents. The filter’s intensity is based on how grey the circular part of the filter is. They can reduce the aperture from anywhere to 2 to 13 stops which come in handy during various shooting situations.

Take note that a “stop” means that the light that usually passes without a filter is halved. Therefore, a three-stop ND filter will only allow 1/8 (1/2x2x2) of the incoming light to pass. Thus, filters that can reduce light for one to two stops are used for intermediate increases in exposure time especially when taking pictures of water. Meanwhile, neutral density filters that have reductions of 10 to 20 stops are often for extreme exposure that works best for blurring subjects in daylight.

Types of Neutral Density Filter

There are three types of neutral density filters: basic, variable and graduated. Basic ND filters are the ones that evenly diffuse light throughout the image. Because of the equal shade, you can mount it to the lens any way you want.  Meanwhile, variable neutral density filters change in shade as you turn the front part of the filter. Use this filter to experiment on the limitless effects that it can bring to the photo.

Finally, graduated neutral density filters feature two levels of light obstruction. This works best during landscape photography especially because the shade of the sky is often different than the ground. Graduated filters bring a positive effect to the camera’s dynamic range which translates to improved image brightness. It also improves image detail and colour by decreasing the photo contrast. Graduated filters come in two types: soft-edge and hard-edge. The latter shows a clear division between the two shades while the former presents a gradual transition.

What to look for in a Neutral Density Filter?

In looking for the right basic neutral density filter, two things must be considered. First, the filter must fit the lens diameter for it to function very well. Second, you must consider the intensity of light refraction that you need. For this, you have to take note of the natural light available and adjust accordingly. If readily available light is intense, then you might need a filter that allows more f-stops.

It’s even trickier when you are in the hunt for a graduated neutral filter. Aside from the filter’s strength, you should also take notice of the filter’s placement in relation to the frame’s horizon. Ideally, the demarcation of the two filter shades is aimed just below the horizon for a smoother and more natural rate of transition.

Filters are classified differently by various brands. Leica quantifies f-stops using legends like 1x, 4x, 8x and so on. Lee and Tiffen categorizes from ND0.3 and it goes up with increments of 0.3 (0.6, 0.9, 1.2, etc.). Finally, B+W, Cokin and Hoya tag their filters with ND2x, ND4x and so on. Each legend corresponds to a certain number of aperture reductions from 1 to 16 2/3. These translate to light transmission rates from 50% to 0.001%.

When to use and not to use a Neutral Density filter

Neutral Density filters are ideal for landscape photography, especially with shots that involve bodies of water. Scenic views can be made more stunning granted that there are no obstructions to the view. That being said, it won’t be wise to use one if any object cuts through the horizon. Otherwise, that item will incur different shades that don’t look natural. Finally, an ND filter saves you post-processing time. Without it, you can still get the desired effects but you would have to digitally combine several shots with various exposures to cover the entire dynamic range.

How to set up the Neutral Density filter with a camera

Before placing the filter, it helps to mount the camera into a tripod first. Place the cable release too before fixing the filter. After doing so, you must set the camera’s exposure settings to the lowest ISO and smallest aperture possible. This will buy you exposure time in terms of shutting speed.

Then, you can then attach the ND filter. If you have a circular filter, you can easily screw it to the lens. But if you have a rectangular filter, you will need a filter holder that is usually attached to an adaptor ring. When the filter is in place, you can try taking a shot to see its effect.