A Primer on Understanding Photographic Filters

Today’s Photo Tips:  Filters are probably one of the least expensive accessories you can add to your camera bag that will make big changes in the way your pictures look. Obviously, the advent of digital photography has changed the use of filters and today’s powerful photo-editing software has eliminated the need for using many of them. Many people that think that if a filter is needed, they’ll just apply one in their photo editing software after the capture, however, there’s a couple reasons why this isn’t the best method. Achieving color filter effects in the digital darkroom can only produce a result similar to the one you would get if you actually used a color filter at the time of exposure. It need really good luck pulling detail and color back from an overblown sky because you were exposing for the foreground. All being said, you should always do everything possible to get the image to look its best in-camera.

Understanding the Various Types of Available Filters: There are many types of filters; UV, Skylight, ND, Polarizers, some often called, “protective” filters, as well as numerous filters for creating black and white images, special effects, color correction, color conversion and light balancing. Far too many to discuss here. Anyone who has ever purchased a lens has had the salesmen offer to sell them a protective filter. Because most digital sensors incorporate UV and IR filters in their designs, UV lens filters are largely unnecessary, regulating the use of a UV filter or a clear filter to form a barrier protecting the lens against grit, grime, and fingerprints. Unfortunately, any filter adds one more obstacle to the clear path of light from the object to the cameras sensor. As such, it degrades the image, even if only slightly and also increases the likelihood of flare and ghosting. The best advice is only use a filter if there is a specific need to use it. Lets take a look at each of these filter types, and their specific uses.

UNIVERSAL USE FILTERS

UV Filters: A UV filter is used to reduce UV rays from entering the lens and striking the camera sensor and will reduce distant haze or fogginess . Because most digital sensors incorporate UV and IR filters in their designs, UV lens filters are largely unnecessary, regulating the use of a UV filter or a clear filter to form a barrier protecting the lens against grit, grime, and fingerprints.

Skylight Filters: A skylight filter (also known as a 1A filter) has a very pale magenta tint which is designed to slightly cut down on blue light and UV light. The effect is mainly for situations where light is slightly bluish such as that light found in hazy or cloudy weather. A good rule of thumb would be that the skylight filter works well for overcast or hazy conditions, but would fall short in open shade or at higher altitudes. While digital cameras can surely get the same benefits from these filters, it is a simple matter to correct color casts using post editing software.

Neutral Density (ND) Filters: Neutral Density (ND) filters are filters that are designed to reduce the amount of light entering through the lens. They come in handy when you’re in a bright light situation and you want to shoot at wider apertures to minimize depth of field or slower shutter speeds to show the motion of water. The come in various densities to reduce light by 1, 2, 3, or more stops. It is possible to stack 2 filters together to increase the density as needed.

Graduated ND (GND) Filters: Similar to the ND filter, GND’s have a gradual change from clear to gray, again in varying degrees of density. They are used when there are significant tonal differences between the foreground and the background. Taking a picture of a beautiful scene can be often spoiled when the camera’s meter properly exposes the sky but leaves the foreground in deep shadow. By using a GND, one can decrease the light from the brighter skies by several stops and properly expose the foreground. GND’s come in hard or soft versions. This refers to the abruptness of the change from gray to clear. Hard GND’s are good when there is a clear delineation at the horizon, such as oceans or flatlands. When trees and mountains are in the scene, a soft GND will help blend at the horizon level. GND’s are generally square and fit in a special holder, such as Cokin, and can be slid up and down inside the slot to align the horizon line to the transition line. .

Polarizer Filters: No camera bag should be without a Polarizer Filter. A polarizer is different than most filters in that it is composed of two pieces of glass, mounted independently inside a round frame so that one can be rotated relative to the other. As it is rotated, it increasingly cuts out glare and haze; you can actually observe this change through the viewfinder. Polarizers reduce glare from water, glass, or any non-metallic surface. It will not reduce glare from metal. You can also use a polarizer filter to darken blue skies. The blue of the sunlit sky is partially composed of polarized light. If you cut down on the amount of this light, you darken the image, so the sky appears darker. Polarizers come in two versions, linear and circular. FYI: Autofocus cameras will perform best with a circular polarizer.

FILTERS FOR BLACK & WHITE PHOTO PHOTOGRAPHY

Filters for BW are used to make one gray tone stand out more from the others. Since colors show up as shades of gray, one must have a way to differentiate between a bluebird and the green background of the tree he’s in. A filter transmits light of its own color and holds back light of other colors. Let me repeat that… A filter transmits light of its own color and holds back light of other colors. A yellow filter transmits light of yellow objects and holds back light of other colored objects. The same holds true for a green filter and a red filter and any other color filter you choose to use. Yellow filters: The darker the yellow of the filter, the darker-gray the sky will appear. For an even darker sky, you can use a green filter and the white clouds will stand out even more. A red filter will produce a sky that is almost black. Of course, filters are used for more than just changing the color of the sky. If you plan on converting your color shots to BW, you should own several different color filters for altering the original capture. Though color filters are pretty much exclusively used by B&W photographers, they might be used to reduce haze, reflections or glare.

Understanding The Effects of Color Filters on B&W Photography: Color filters allow the black and white photographer to exercise some selective control over the color tone values of an image. Using color filters on an intended black and white final digital outcome affects very much the look and effect the final image will have. Color filters work by cutting on light of their complementary colors and passing light of their same color, thus the lightening effect of similar colors and the darkening effect of complementary colors. Remember though that this act of cutting light means less light making it through the lens and onto the digital sensor, often requiring longer exposure times to make up for light loss. There are 5 filter colors that are commonly used in black and white photography - red, orange, yellow, green, and blue. Each lets through its own color of light and blocks other colors to varying degrees. The result is that colors matching the filter color appear brighter in the final image, while other colors appear darker. In black and white photography this means that objects appear as lighter or darker shades of grey.

Yellow Filters: Yellow filters are probably the most widely used, producing the most subtle effect of the 5 colored filters. In some cases the difference is barely noticeable, but it can help to lift a photo just enough. They offers an accurate tone range in compensating for the blue sensitivity of the camera sensor by slightly darkening sky and increasing contrast between blue sky and clouds. They also may help reduce haze. In portrait photography, they produce warm, natural, pleasing flesh tones, reducing freckles and red spots on skin and darkening blue eyes. Its effects are similar to that of an orange filter but less intense. Yellow filters are also good for separating shades of green, and can be used when photographing plants to increase the contrast of foliage. [It lightens: Yellow, Chartreuse, Olive, Red, Pink, Orange, and Lime Green; it darkens: Blue, Violet, Purple, and Lilacs] (hint: Increase f/stop +1)

Orange Filters: Orange filters sit between red and yellow filters, giving a nice balance of each one's properties. This makes them a popular general purpose filter. In portrait photography, an orange filter gives warm, smooth skin tones, reducing the appearance of freckles and blemishes, giving the skin a healthy, smooth look. When photographing buildings and cityscapes, they give bricks a more pleasing tone, and increase contrast between different materials to add depth and texture to the image. Similar to red filters, they can be used to reduce the appearance of fog and haze, and to darken skies and emphasize clouds.

Red Filters: Red filters produce a very strong effect and greatly increase contrast. They're often considered too "harsh" for most types of photography, but can be used to produce striking creative effects. In landscape photography, a red filter produces very dramatic skies, turning a blue sky almost black and making clouds really stand out, giving the scene a dramatic feel. They're also excellent for increasing visibility in haze and fog. When shooting plants they help increase definition between flowers by darkening the surrounding foliage. This is particularly useful when shooting red flowers, as they have a similar tone to the surrounding leaves. In summary, a red filter will let red light through, but block most green and blue. [It lightens: Reds, Pinks, Magentas, some Browns, Yellow, and Orange; it darkens: Blues, Greens, and Cyan] (hint: Increase f/stop +3)

Green Filters: Green filters are less popular than the others but are useful in some circumstances. A green filter lightens greens, separating foliage and flowers. A green filter is mainly used for photographing plants as it helps separate the green foliage from the brightly-colored flowers and buds. They can also be used in landscape photography to boost the appearance of grass and trees, but they also lighten the sky so you need to be careful not to lose detail there. Occasionally they are used to produce pleasing skin tones in portraits. [It lightens: Yellow, Yellow-green, Olive, and Greens; it darkens: Blue, Violet, Magenta, Red, and Maroon] (hint: Increase f/stop +2)

Blue filters: Blue filters are rarely used for black and white photography as they darken most colors and reduce contrast across the entire range of an image. However, when used correctly, this reduced contrast can be useful for giving a shot a calm, soothing atmosphere. A blue filter also increases the appearance of haze and mist, making it handy for enhancing the mood of an early-morning scene. In Summary

If you’re a serious outdoor photographer, the judicious use of filters at the right time can vastly add to the resulting quality of your image. If you're serious about taking pictures for conversion to black and white, then a selection of colored filters is a great addition to your kit. They'll give you much more control over the way your photos appear, helping you to create mood, balance contrast, and emphasize the most important parts of a scene. Which filter should you buy? In the “Universal” category above, a circular Polarizer Filter and a GND Filter would be the top two choices. If your looking for a lens protector, choose a Yellow Filter. Not do you only get lens protections, you get the benefit of the subtle changes made by this filter, as well as its benefits for landscape photography where the effect on blue is just enough to make a light sky a shade darker than the print's border. After this, choosing a Red Filter will probable provide you with the most use for creating Black & White photographs. Some of the more popular brands are Cokin, Lee, and Singh-Ray. Cokin filters are a great starting option as they are more budget-friendly and give reasonable quality while the more expensive filters will be much higher build quality and will give better, and more consistent results as well as less color casting from stacking multiple filters. As a final note, remember that all filters reduce the amount of light available to some degree. For instance, a polarizing filter will reduce light anywhere from 1 to 2 f/stops, requiring you to compensate for this light loss. If you are using an automatic camera with TTL metering, this shouldn’t be an exposure issue, but is worth mentioning as you’ll find yourself in situations where the light loss is significant enough to force you into using slower shutter speeds or wider apertures, and possibly a tripod.