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One of the easiest ways to improve your images is to use camera filters but like so much in the photo world, life is rarely that simple. Thats because photographers seem to be of two minds about filters: Some purists don’t like them because they abhor anything coming between reality and the captured image. True filter fans worry less about resolution charts and just like to have fun with their photography. If thats you, read on
Camera filters absorb light and that light loss must be compensated for when calculating exposure. Your digital SLRs in-camera metering system compensates for these differences but the filter factor is still a good measure of the number of stops that must be compensated for by either automatically or otherwise altering shutter speed, aperture, or ISO.Filter factors are multiples of the unfiltered exposure so that a factor of two equals a one-stop increase.
A Polarizer can deepen the intensity of blue skies, as well as reduce or eliminate glare from non-metallic objects. Many manufacturers offer Warm Polarizers, including Hoyas Moose Filter, named for nature photographer Moose Peterson, that combines a polarizer and a warming filter. Polarizers are available in traditional linear or circular versions. Take the time to read your cameras manual to find out what kind you need for your specific SLR and purchase the proper one for your specific camera. When buying filters there is one overriding concern that should be followed: Don’t put a $19.95 filter on a $1,000 lens. You should purchase the best filters that you can afford and than mean you should look at filters from B+W, Heliopan, and Singh-Ray. Yes, they will be expensive, but if you are in pursuit of The Ultimate Image that shouldn’t deter you. Get a piggy bank and save those pennies!
If you want to get the ethereal effect of blurring while photographing moving water and can’t select a slow enough ISO speed, neutral density (ND) filters placed in front of your lens allow you to use slow enough shutter speeds to photograph waterfalls or river flow over rocks. Neutral density filters absorb light evenly throughout the entire visible spectrum,effectively altering exposure without causing a color shift. ND filters areavailable in different densities of gray and are rated by how many f-stops they decrease your aperture settings.
One of most useful tools in my filter toolkit are graduated density filters sometimes called gradient filters or grads. These filters have a clear area at the bottom and somewhere around the middle, start blending into an area of increasing color or neutral density. Graduated density filters allow you to control areas of excessive brightness such as a sky and bring them into balance with the rest of a scene by darkening and possibly adding color. The colored area of these filters covers less than half of the filter, but the effect can be adjusted by moving the filter up and down vertically or by rotating the filter folder, so there is no pressing requirement to split the image in equal and perhaps boring parts.
Most companies make color graduated neutral density filters that take what you see and kick it up notch. The final effect of using graduated density filters will vary based on the distance of the filter from the front of lens and the density of filter used. The effect is more pronounced when a wide-angle lens is used at small apertures, with just the opposite effect is produced at wider apertures with longer lenses. Other graduated filters add colors ranging from mauve to brown and are in pairs of the samecolor, with one having a mild effect with the other, darker one, being used to create more dramatic effects.
Joe is the co-author of Better Available Light Digital Photography” published by Focal Press.