Sometimes you have too much light, and that’s where Neutral Density (or ND) filters come in. Neutral Density filters are designed to simply reduce the amount of light that gets to your camera. They are dark filters that typically come in 1, 2 or 3 stop reduction increments, and are most often used outdoors under bright sunny conditions.

With most shooting situations (especially indoors or under low light) the issue is the opposite, so it’s hard to imagine needing less light. Typically, you need more light, faster shutter speeds, etc. That’s why ND filters are often used for landscape photography, where during a bright sunny day, light is in abundance. This may simply be because of the light amount, or because you have light hitting off a highly reflective surface such as sand, water, or snow and ice.

Left side with no ND filter, Right side with an ND4 filter.

Reduce the Light Intensity

Maybe you want to simply reduce the amount of light in the picture. All cameras have a maximum shutter speed they can attain, and every lens has a widest aperture they can open up to. If you have too much light, it can strain these limits. Also, every lens has a sweet spot which you may want to shoot in, which could require less light to achieve.

Slower Shutter Speed

If you’ve ever shot a picture of running water, you’ve likely tried using a slower shutter speed to indicate motion. There are a variety of other scenarios where using a slow shutter speed may be the technique required to get the shot, but you can only slow down the shutter speed if you can reduce the amount of light. If your aperture is already at it’s minimum, an ND filter will let you cut out some light so you can achieve this.

Wider Apertures

Perhaps you want a low depth of field in your picture, or (as above) you’re looking to shoot at your lenses optimum aperture for the best sharpness. If you have too much light in the scene, the camera will struggle to not blow out the image at wider apertures, so an ND filter will help you out immensely here.

Graduated ND Filters

Finally, you can buy graduated ND filters which go from dense (dark) to light in a gradient pattern on the filter. These are handy when only a portion of the image is bright (like the sky) and a portion is darker (like the ground). It will help to achieve exposure balance.

If you’re a photographer who shoots outdoors a lot, you’ve likely scrutinized closely the outdoor photos from other photographers, and in doing so – you may have noticed deep blue skies, crisp lines on green surfaces, or generally higher contrast. These are pictures that were (in all likelihood) shot through a polarizer.

What a polarizer does is to remove stray waves of light, which cause reflections. By doing this, they can increase the clarity of foliage (which often reflect a degree of light), remove the reflection on the top of water, and increase the color saturation (particularly in blues and greens). Clouds will pop, trees will stand out, and images will generally appear richer.

Polarization dangers

Polarization is a great effect, but it can be overused. At high altitudes, where there is very little atmosphere to help scatter the light – or even at sea level on a crisp, clear day. Too much polarization can cause the sky to go navy blue (or close to black). Not good.

Also, because the polarizer is quite dense, it can cause your wide-angle shots to experience dark edges if you aren’t careful. To combat this, you can get a “thin” polarizer, which are more expensive, but will help remedy this vignetting problem.

Finally, make sure that you use a circular polarizer with a Digital SLR, as a linear polarizer could cause trouble with the autofocus sensor in your camera.

Using a Polarizer

The polarizer effect only functions when it is rotated in proper relation to the scene you are shooting. You’ll still get the benefit of increased contrast and saturation without doing so, but the reduction of glare can only be achieved this way.

Circular polarizers rotate, and when you rotate one, you’ll see stuff happening in your viewfinder. What you’re doing is lining up the etching on the filter with the stray waves of light. What you’re looking for is a reduction in glare off surfaces, and for an increase in the contrast between sky and clouds. Metering will all be handled in-camera with the filter attached by the camera’s internal metering system.

Bear in mind that when some lenses focus, the end element (which the filter is attached to) also rotate, so you will need to use a little forethought if this is the case, by focusing first, polarizing after.

Have fun!