Essential Filters

   Although for some people programs such as Adobe Photoshop have reduced the need for filters, there are still some filters that we regard as being essential items in a well-stocked camera bag. Others that we’ll mention here may not be totally essential, but they help modify the light in specific ways and let you create images that would be difficult or impossible without them. Not all digital cameras can accept filters, and some can only use proprietary filters designed by the manufacturer. To accept standard screw-on filters, the front of the lens must have a threaded ring. If your lens has this feature, there should be a number indicating the size of the filter that will fit on the lens. 

Here are filters to consider:

   Skylight filters. These filters are clear glass and are mainly used as protective covers for the lens. If there is an impact to the front of the lens or contact with an abrasive surface, the filter will take the brunt of the punishment and spare the front glass lens element from being damaged. We suspect that there’s also a certain amount of add-on selling here by camera shops and online dealers, but the basic premise makes sense and we use them as lens protection. A $20 to $40 filter is less painful to write off than an expensive lens costing hundreds of dollars.

   Polarizing filter. Of all the filters that we carry in our camera bags, we’d have to say that a polarizer is the one filter we just wouldn’t want to be without. Like all filters, a polarizer modifies the light as it enters the lens. Chief among these modifications is a polarizer’s ability to remove some of the glare and reflections from the surface of glass and water. It also excels at darkening blue skies and boosting color contrast and saturation. The quality of light in a scene can be made clearer and less hazy. The amount of polarizing effect you get depends on a few variables, including the time of day, the angle of the light relative to the scene you are photographing, and the reflective properties of a given surface.  The best type of polarizing filter to use on an autofocus SLR camera is a circular polarizer. Don’t use a linear polarizer with an SLR, because it can confuse the camera’s autofocus and metering systems. A circular polarizer allows you to rotate a circular ring on the front of the filter and adjust the level of polarizing effect until you get it just right. Polarizers are darker filters that cut down on the amount of light entering the lens, and this usually means using a wider aperture or a slower shutter speed. Since they reduce the light entering the lens, they are easiest to use on cameras that use TTL metering (through the lens) so you don’t have to calculate a compensating adjustment. For rangefinder cameras that also feature an LCD screen that shows you a live preview of what the lens sees, circular polarizers can be used in much the same way as you would with a DSLR, by rotating the ring until the effect looks best. The only drawback is that these screens can be somewhat hard to see in bright light, which makes it more difficult to evaluate the polarizing effect. Seán has been able to use his larger circular polarizing filter on a smaller compact camera by simply holding it against the front of the lens. Since the preview on the LCD is sometimes hard to see, to judge which rotational angle is best, he first holds the filter up to his eye and turns it until the effect looks good. Then he places it in front of the lens, making sure to keep the filter rotation the same. Fortunately, his Tiffen (tiffen.com) circular polarizer has a small handle for turning the ring that makes it easy to use as a positioning marker. If you’re using a polarizer on a rangefinder camera that does not also have an LCD screen showing what the lens is seeing, you won’t be able to see when the polarizing effect is best, so your success will be somewhat hit or miss. For this type of camera, especially if it does not use TTL light metering, a linear polarizer is best. You’ll also need to factor in a plus-1 or plus-2 stop exposure compensation to adjust for the darker filter letting less light through the lens. Few things liven up an outdoor shot on a sunny day like a polarizing filter. Although you can use image-editing software to darken a blue sky and add some saturation into the colors of an image, it doesn’t replace a good polarizing filter.

   Neutral density (ND) filters. These filters reduce the amount of light that enters the lens. Since they are neutral, they do not affect the color balance of a scene. ND filters are used for times when you want to achieve a certain effect, such as shallow depth of field produced by a wide open aperture, or a motion blur from a slow shutter speed, but the lighting conditions are too bright to allow the necessary settings. Flowing water is a classic subject for a slow shutter speed treatment, as is long grass blowing in the wind. By placing a dark ND filter on the lens, you cut down on the amount of light, making the wider apertures and slower shutter speeds accessible (Figure 3.37). ND filters are commonly available in 1-, 2-, and 3-stop increments, and darker ND filters can also be ordered that will cut back as much as 5 stops of light (Figure 3.38). For times when you need a really strong ND filter, you can stack them together to increase the darkening effect.

    Graduated ND filters. Graduated ND filters are dark on the top half and then gradually fade to transparent along the middle of the filter. They are used in situations where the sky area of a landscape shot is much brighter than the terra firma below the horizon. By using the filter to darken the sky, a more balanced exposure can be made for both the earth and sky portions of the image. Standard graduated ND filters that screw onto the front of the lens are less than ideal since you can’t adjust the placement of the horizon line; it’s always right through the middle of the filter. A better approach is offered by Singh-Ray (singh-ray.com) with its Galen Rowell Graduated ND filters. Designed by the late, renowned nature photographer, these filters come in a range of densities and also feature either a hard-edged or soft-edged gradient transition from dark to transparent. Since the filter is a rectangular piece of acrylic that fits into a standard Cokin P-series filter holder, the photographer can adjust the graduated edge of the filter up or down to match the location of the horizon in the image. This makes them ideal for compositions where the horizon line is not centered. The advent of digital cameras has introduced a new way of achieving this effect that involves shooting two (or more) exposures on a tripod, with each one exposed for a specific area in the image. The different exposures can be blended together in the digital darkroom either manually or via an HDR process. If multiple exposures and digital postproduction seem like too much hassle, or if you simply prefer to do as much as possible in the camera and on location, graduated ND filters are an elegant solution to a common photographic problem.