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Filters allow added control for the photographer of the images being produced. Sometimes they are used to make only subtle changes to images; other times the image would simply not be possible without them. The negative aspects of using filters, though often negligible, include the possibility of loss of image definition if using dirty or scratched filters, and loss of some Exposure . The former is best avoided by careful use and maintenance of filters, while the latter usually will not be a problem if planned out properly. Many filters are identified by their Wratten Number . USES OF FILTERS IN PHOTOGRAPHY Filters in photography can be classified according to their use:
Clear and ultraviolet Clear filters, also known as '''window glass''' filters or '''optical flats''' are (ideally) completely transparent, and thus not (technically) really filters at all. They are generally used to protect the front of a lens. UV (ultraviolet) Filters are also often used for this purpose. While in certain cases (such as harsh environments like Desert s or Mud Wrestling rings) this is obviously necessary, there is a debate within the photographic community as to whether or not this is a sound practice. Naysayers claim:
People in favor of the practice claim:
Color correction A major use is to compensate the effects of lighting not balanced for the film stock's rated used with daylight film corrects the orange/reddish cast of household tungsten lighting, while the 85 used with tungsten film will correct the bluish cast of daylight. Color correction filters are identified by numbers which sometimes vary from manufacturer to manufacturer. lighting, it can also be used to oversaturate scenes that already have blue. The photo on the left was shot with a polarizer, while the one on the right was shot with a polarizer and an 80A filter]] Color subtraction Color subtraction filters work by absorbing certain colors of light, letting the remaining colors through. They can be used to demonstrate the primary colors that make up an image. Contrast enhancement Filters are commonly used in Black And White photography to manipulate Contrast . For example a yellow filter will enhance the contrast between clouds and sky by darkening the latter. Orange and red filters will have a stronger effect. Polarizer A Polarizing filter, used both in color and Black And White photography, can be used to darken overly light skys. Because the clouds are relatively unchanged, the contrast between the clouds and the sky is increased. Atmospheric haze and reflected sunlight are also reduced, and in color photographs overall color saturation is increased. There are two types of polarizing filters. A linear polarizer filter creates linearly Polarized light. A circular polarizer creates circularly polarized light, by adding a second Birefringent layer to the filter after the linear polarizer. The metering and auto-focus sensors in certain cameras, notably SLRs , will not work properly with linear polarizers, both because of the mirror and because of the beam-splitters used to split off the light for focusing and metering. Circular polarizers will work with all types of cameras. Cross screen A cross screen filter creates a star pattern, in which lines radiate outward from bright objects. The star pattern is generated by a very fine Diffraction grating embedded in the filter. Diffusion A Diffusion Filter softens subjects and generates a dreamy haze. MATERIALS AND CONSTRUCTION Photo filters are commonly made from Glass , Resin plastics similar to those used for eyeglasses (such as CR39 ), Polyester , or Gelatin . Sometimes a color is blended throughout the filter material, in other cases the filter is a sandwich composed of a thin sheet of material surrounded and supported by two pieces of clear glass or plastic. Certain kinds of filters use other materials inside a glass sandwich; for example, Polarizers often use various special films, netting filters (a kind of Contrast Filter ) have nylon netting, and so forth. The rings on screw-on filters are most often made of aluminum, though in more expensive filters brass is used. Aluminum filter rings are much lighter in weight, but can "bind" to the aluminum lens threads they are screwed in to, requiring the use of a Filter Wrench to get the filter off of the lens. Aluminum also dents or deforms more easily. FILTER SIZES AND MOUNTINGS Manufacturers of lenses and filters have "standardized" on several different sets of sizes over the years. Threaded round filters For circular filters, standard sizes include 49 mm, 52 mm, 55 mm, 58 mm, 62 mm, 67 mm, 72 mm, 77 mm, and 82 mm; within this range, other sizes may be hard to find. The Thread Pitch is 0.5 mm or 0.75 mm, depending on the ring size. Square filters For square filters, 2" x 2", 3" x 3" and 4" x 4" were historically very common and are still made by some manufacturers. 100mm x 100mm is very close to 4"x4", allowing use of many of the same holders, and is one of the more popular sizes currently (2006) in use; it is virtually a standard in the Motion Picture industry. 75mm x 75mm is very close to 3" x 3" and while less common today, was much in vogue in the 1990s. A French manufacturer called Cokin makes a wide range of filters and holders in three sizes. "A" (amateur) size is 67 mm wide, "P" (professional) size is 84 mm wide, and "X Pro" is 130 mm wide. Many other manufacturers make filters to fit cokin holders. Cokin also makes a filter holder for 100 mm filters, which they call the "Z" size. Rectangular filters Graduated filters of a given width (100 mm, 67 mm, 84 mm, etc.) are often made rectangular, rather than square, in order to allow the position of the gradation to be moved up or down in the picture. This allows, for example, the red part of a sunset filter to be placed at the horizon. Bayonet round filters Certain manufacturers, most notably Rollei and Hasselblad , have created their own systems of Bayonet Mount for filters. Each design comes in several sizes, such as Bay I through Bay VI for Rollei, and Bay 60 through Bay 93 for Hasselblad. Series filters From the 1930s through the late 1970s, filters were also made in a sizing system knows as a series mount. The filters themselves were round pieces of glass (or occasionally other materials) with no threads or rings attached. Instead, the filter was placed between two rings; the mount ring screwed into the lens, the retaining ring held the filter against the first ring. The series designations are generally written as Roman Numerals , I through IX, with the interesting exception of the series 4.5 filter. STUCK FILTER REMOVAL A stuck filter with an aluminum ring should not be removed by squeezing from both sides with your hand; aluminum deforms and this could permanently warp the filter, damaging it and also making removal even more difficult. If the filter is stuck and a filter wrench is not available, cup the whole filter with a piece of fabric and press it down against something solid. Then twist the lens barrel to unstick things. SEE ALSO EXTERNAL LINKS |
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