Photographic Filters, Part 2: Polarizers and Neutral Density Filters

We talked about filters for Black and White photographs (An Introduction to Photographic Filters). Now, let’s take a look at a few filters that can be used in both Color and Black and White photography. Unlike red, yellow, green and blue filters, which create vastly different effects in black and white than they do in color, polarizers and neutral density filters work similarly in both color and black and white photography.

Polarizing Filters

Polarization occurs when a lot of light rays vibrate along the same plane. Polarizing Filters are made of two panes of glass with tiny crystals. By rotating the filter 90 degrees, the crystals will block the polarized light that travels perpendicular to the filter plane. The effects are dramatic.

Polarizers will:
1. Deepen blue skies
2. Increase color saturation
3. Remove / Reduce glare and reflections in water and glass
4. Cut through haze
5. Increase contrast

Be aware that there is a Filter Factor with polarizers. Polarizers absorb light. In turn, that will effect the amount of light that penetrates the filter and reaches the digital sensor / film. The manufacturer will assign a Filter Factor to the filter identifying the number of f-stops necessary to correct the exposure. Also, some wide angle lenses may need thinner filters to avoid vignetting.

Circular Polarizer

No Polarizer

The effect of a polarizer can not truly be replicated post-production (yet, anyway). Yes, saturation can be increased, blues can be darkened, clouds can be lightened but removing reflections off water and glass can not be done with the same results that the filter will achieve. This is an instance where using the filter will capture more usable information and start you out on a better foot in your photo editing software.

There are two types of polarizers:
1. Linear – used with cameras that don’t have silvered mirrors (will NOT work with SLR’s)
2. Circular – works with all cameras
If you’re unsure which type of filter you need, read your camera’s manual.

Neutral Density Filters

Neutral Density filters are gray filters that block all colors of light, equally. They are used to reduce the amount of light entering the lens. Use an ND filter to prevent overexposure when you’d like to use a slower shutter speed or larger aperture in a bright scene. ND filters are available in a variety of densities, with different filter factors.

Use a Neutral Density Filter to block light in bright scenarios when you want to:
1. Slow down your shutter speed
2. Shoot at a faster f-stop

With long exposures, moving objects will disappear. In this photograph, the cars disappeared but the streaks of light from their headlights remained.

Reasons you’d want to Shoot at a Slower Shutter Speed:
1. Capture motion in waterfalls – softer water, less droplets, more streaks
2. Soften a sky – moving clouds + slower shutter speed = softer sky
3. Smooth the water of a lake or ocean – get rid of ripples and waves with a slower shutter speed.
4. Action shots – runner + slower shutter speed = streaks illustrating motion. Bird flapping wings, race car, dog running, etc.
5. Fade moving objects – With a slow enough shutter speed, moving objects will disappear.

Reason you’d want to Shoot at a Faster f-stop
1. Isolate subject with shallow Depth of Field

Using the shutter speed I wanted, without an ND filter, caused overexposure.

The Neutral Density Filter allowed me to achieve a proper exposure and still use all the settings I needed to capture motion blur

Split Neutral Density Filters also called Graduated ND Filters

Split ND Filters are half clear and half neutral density. The density lessens as it nears the clear half of the filter. This will produce a subtle blending effect. Split ND filters are especially helpful in landscape photography when the brightness of the scene is not uniform. Like regular ND filters, it is color neutral, meaning that it’ll lessen the light but not effect the colors.

These filters also come in a variety of densities. When using, rotate the filter to position the dense area of the filter over the bright area of the scene.

Use a Split Neutral Density Filter when:
1. the sky is several stops brighter than your land
2. the foreground is in shadow, and the background is brighter (or vice versa!)
3. shooting reflections in water (reflections often have a different exposure value than the rest of the scene)
4. using flash will cause your foreground to overexposure

There are two types of Split ND Filters

1. Hard step – an abrupt gradation of density to clear
2. Soft stop – a smoother gradation to clear
The scene dictates which is the best option to use. The Hard Step is nice for when shooting defined horizon lines.

No split ND Filter

Split ND Filter