by Roger Devore
Most nature photographers use some type of filters to improve their images. Polarizers, warming, split neutral density, and enhancing are terms associated with different types of filters that I use most often with color photography. Each has specific characteristics that can help to make better images when used in the correct situation. Learning when to use filters will improve your image quality and make your images more like what you visualized when you composed them in the view finder.
Without a doubt, the filter that Lonnie and I use most is the polarizer. You will find one on our lenses more often than not. A polarizer is a round filter that screws into the filter threads on the end of the lens. They come in a variety of sizes and you need to buy the one that corresponds to the filter size of your specific lens. After the filter is attached to your lens, the filter will still rotate. By rotating the filter, you can control the amount of polarization and actually see the effect of the polarizer in your view finder during the rotation. Polarizers come in two types, linear and circular. Circular polarizers are required for auto focus cameras for the focus and exposure modes of the camera to operate correctly. Linear polarizers work well on all other cameras. Polarizers have the most effect on the image if the sun is 90 degrees from the area in your view finder or when the sun is over one of your shoulders as you look through your camera. Many polarizers come with an index mark on the filter itself. Maximum polarization will also occur if that index is rotated to point at the sun. Like everything else in photography, you pay a price for the polarizer. It removes 1.5 to 2 stops of light when it is attached to your lens. If you are metering through your lens, your camera will automatically compensate your exposure and you need to do nothing else. If you are metering some other way, then you need to compensate for the filter in your final exposure before setting it on your camera.
Polarizers can do several different things to improve your images. First, they will darken blue skies and improve the overall contrast of the scene making all colors look more colorful and saturated. This technique is most useful on bright sun shiny days and will make clouds in the sky look much improved. Again, the most dramatic effect will occur when the sun is 90 degrees from the direction your camera is facing. By rotating the filter as you look through the lens, you can choose the amount of polarization that you like best.
Polarizers can also be used to cut down glare and reflection. For nature photography this is most useful when making images of water. A polarizer often makes it possible to filter out the reflection in water so that you can see through it to what is underneath. This technique is very useful for seeing rocks that are under water and otherwise would not be visible. Again, by looking through your viewfinder and rotating your polarizer, you can see the effect the filter will have on your film.. The polarizer will also work to cut down unwanted reflections when you are trying to shoot through or around glass.
Lastly, polarizers can be very useful for clearing images on a hazy day. The filter will polarize the individual particles in the air causing the haze and help to make the final image less hazy. Pollution and haze are constantly becoming more of a problem for nature photographers even in places like National Parks. The polarizer can help get useable images that might not be clear enough otherwise.
Warming Filter are used to slightly warm the color of an image. Warm colors are reds, yellows, and oranges. Cool colors are blues and greens. Some nature situations are naturally rather cool in color. Some examples are early morning, late evenings and images in shade. This type of lighting will usually have a cool blue cast on film. A warming filter will remove some of this blue and make the image warmer and usually more appealing to the eye. The most used warming filters are designated 81 A, B, and C. The A, B, and C designation refers to the degree of warming effect, the A being the least and the C being the most. Warming filters also have a exposure light loss (filter factor ) associated with them that varies according to the individual filter. Again, if you are metering through the lens, the camera meter will automatically compensate for the filter and set the correct exposure. If the coolness of the light occurring is not what you desire, try these filters.
Split Neutral Density Filters
In nature photography, we use slide or transparency film almost exclusively. One of the drawbacks of slide film is the limited exposure latitude, or the amount of light difference or contrast that the film can record and still give usable exposures in the bright and dark areas of the image. Our eyes can see a much greater difference that the film can record, so often our film will come back with no details in the dark areas or details there but the light areas overexposed. A split neutral density can help overcome this problem. These filters are rectangular in shape (stay away from the round ones) and are dark on one end and clear on the other. The dark area takes away light but does not change the color of the image. The dark area is available in different densities for different lighting situations. You can buy a one, two, or three stop filter where the dark area removes that much light from the image. The filters also are available in hard or gradual transition between the dark and clear. The gradual filters start darker at the top ad gradually get lighter until they are clear at the bottom. The hard filters have one density of darkness and then become clear with a hard line, no gradual transition. These filters are made in glass or plastic with a wide variation in cost. You also need a filter holder that attaches to your lens and has a slot on each side so that the filter can slide up and down your lens. Cokin make an inexpensive system that is good for starters, although their filters are gray and not actually neutral density. There might be a slight color change with the Cokin filters, but it will be hardly noticeable.
Let’s assume you are making an image that has mountains in the background that are well lit by the warm, late afternoon sun. In the foreground is beautiful stream that is in shade. If this image was made without a filter, the stream would go completely dark and have no details if the mountains were correctly exposed. By metering the mountains and then the stream, you can calculate the exposure difference between the two. With a spilt neutral density filter, you can more even out the exposure so that both areas will record on your transparency film. With the rectangular filters you can move the filter up and down in the holder to place the line of the filter on the actual light and dark areas in the image. The difference in the exposure of the bright mountains verses the dark stream determines which density of filter you would use. Experiment and decide which variation you like best. Maybe you will like the same exposure on the mountain and the stream or maybe you will prefer the stream one stop darker? Only you can decide for sure, both will yield properly exposed image leaving the choice to personal preference. With different density of filters you will get more choices in the final image. Split neutral density allow you to make images that slide film latitude would otherwise prohibit. Play and experiment with different densities of filters and see which work best for you.
Enhancing filters (also called intensifiers) are designed to enhance the colors of one particular part of the color spectrum. The most common enhancing filter boosts reds, yellow, oranges and browns (warm colors). They advertise that they only change the color of those shades and do not effect the other colors in the image. I do not believe that is true, they seem to change everything in the image, but sometimes the change might still useful. This filter is very good for fall color scenes, red rocks of the southwest and any image that has warms tones that would look better enhanced. I have also heard that some company has also designed a similar filter for the green side of the spectrum, but I have never used it. Some people like the effect of the enhancing filters and some think its does too much. My advice is try it yourself and form your own opinion.
Some photographers boast that they use no filters in their photography, but I consider filters another artistic tool to help you make the image that you want. Whether you are using filters to make an image look better than it actually does or to make up for short falls in imperfect film, filters are another avenue to creativity in your photography.