During our workshops and tours we frequently find that people want to know what filters we carry when we create images in the field. The information listed below provides a starting place for filters you might consider when your photography takes you outdoors.
Polarizing Filter: A polarizing filter has been considered a sky-darkening filter for many years; photographers also know that it can be used to remove reflections from shiny surfaces. For outdoor photographers, shiny surfaces include bodies of water and shiny foliage. Youve probably heard that polarizing filters are used at a 90-degree angle to the sun, if you wish to use them at their maximum effect. To find this angle, stand with your back to the sun and extend your arms straight out from your shoulders. The direction to which each arm is pointing will provide maximum polarization. Naturally, you will receive some benefit from the polarizing filter if the angle between your camera and the sun is less than 90 degrees. How much benefit youll receive depends on this angle.
The easiest way to see the effect of this filter is to face toward the direction you wish to photograph and hold the filter up to your eye. View the scene while turning the filter, and you will see the effect it will have on your photograph. We use the Cokin P-size filter system because we can leave the Cokin filter holder on the camera lens while viewing the scene. Additionally, using this system means we only have to purchase one set of filters, which keeps our expenses down and our camera bag lighter.
Warming Filters: The 81-series filters are warming filters. These filters add warmth to a scene in small increments. The series includes 81, 81A, 81B, 81C, 81D, and 81EF. The 81 filter provides the least warmth; the 81EF filter provides the most warmth. (The 81 filter adds very little to a scene, so we dont recommend using it.) This series of filters is designed to counteract the blue/cyan colors frequently seen in the sky, by adding the opposite color to your image. Because the sky contains both blue and cyan (blue-green), these filters are a combination of red and yellow dyes. Unfortunately, the combination of blue and cyan varies with the time of day, season of the year, location and altitude. This variation in color creates a problem for filter manufacturers: they cannot make a set of filters to meet a definite condition because the conditions are always changing. As a result of these inconsistencies, each filter manufacturer has created an 81-series of filters that is consistent within their brand but usually cannot be substituted into another manufacturers filter series.
What this means for you is simple: buy one manufacturers brand, and stay with it. Buy the largest size you need and use step-up rings to adapt the filters to your smaller lenses, or buy a set of filters from a manufacturer such as Cokin that can be used with a filter holder on every lens you own. We have screw-on glass filters for our lenses. We prefer B+W, Tiffin, or Hoya; the filters made by Canon and Nikon are great, too, if you can find the ones you need.
We dont carry the whole set of warming filters. We put an 81A filter on each lens we own and carry an 81B in the largest size well need, along with step-up rings to adapt the filter to our smaller lenses. We use this filter frequently because we find ourselves photographing early in the day and/or in shadows, which means a blue cast is present on our scene. The 81A filter helps to remove this blue color cast. Combining an 81A and 81B will give you the same warming properties as an 81C without carrying an additional filter. Carrying the 81D and/or 81EF probably isnt necessary, unless you find yourself creating images frequently in overcast or shaded light.
Having said that the reflected sky light is variable, we might need or want another warming filter besides the 81A. Also, we might wish to emphasize the cool blue light of the early morning. We can remove the 81A filter to allow more blue light to record on our film, or we might add a warmer filter, such as an 81B or 81C.
The decision to allow more blue light to be recorded on our film brings up another topic that well save for another month: film choice. By now youve probably heard that each color transparency film has its own color palate. Some films emphasize the warmer (red, orange, yellow) part of the visible spectrum; other films emphasize the cooler (blue, green, violet) part of the spectrum. Thus, using the warming filters becomes a creative endeavor that includes consideration of the film well be using and the final color rendition we wish to include in our image.
Split Neutral Density Filters: Our last set of filters includes a one-stop split neutral-density filter and a two-stop neutral-density filter. These filters must be rectangular filters that fit into a filter holder for rectangular filters, such as the Cokin P-style filter holder. Round split neutral-density filters that screw onto the camera lens are worthless. The rectangular filter can be adjusted up or down in the filter holder to divide your image into two portions: one portion that needs a reduction in the amount of light reaching the film, and the other portion that doesnt need any reduction in light transmission. Be sure the filters are neutral density filters; some manufacturers call them gray neutral-density filters. Describing the use of split neutral-density filters is much harder in print than demonstrating its use. Find someone who uses them and buy the person lunch after they show you how to use this wonderful tool, or take a workshop with a knowledgeable instructor.