Filters

Transcript

FILTERS Light that falls on a surface can be reflected, absorbed or transmitted. The perception of the color of objects depends upon the spectral quality of the reflected or transmitted light. When illuminated with white light, an opaque white object appears white because the surface reflects a high proportion of the incident light, and a black object appears black because it reflects only a small proportion of the incident light, non-selectively. In contrast, a red object appears red when illuminated with white light because it selectively absorbs most of the blue and green parts of the white light and reflects most of the red part. Photographic filters function by removing part of the incident radiation by absorption or reflection, so that the transmitted radiation is of the desired spectral quality. Filters, of course, cannot add anything to the incident radiation – a red filter cannot transmit red light if there is no red light in the radiation falling on the filter. PHOTOGRAPHIC FILTERS In photography, a filter is a camera accessory consisting of an optical filter that can be inserted in the optical path. The filter can be a square or rectangle shape mounted in a holder accessory, or more commonly, a glass or plastic disk with a metal or plastic ring frame, which can be screwed in front of the lens. 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 increased exposure required by the reduction of light transmitted. Photographic filters are commonly made from glass, resin plastics similar to those used for eyeglasses (such as CR39), polyester and polycarbonate; sometimes acetate is used. Historically, filters were often made from gelatin, and color gels, also called gelatin or simply gel filters are still used, but these are no longer actually made from gelatin, generally instead made from one of the plastics mentioned above. High quality filters have multiple layers of optical coating to reduce reflections and to allow more light to pass through the filter. Manufacturers brand their high-end filters with different labels, for example B+W: MRC (Multi Resistant Coating). Now several filter manufacturers make “plug-ins” that can be added to your computer software programs such as Photoshop, Photoshop Elements 2.0, Corel Photo-Paint, Aperture, and Lightroom as well as other compatible programs. Photoshop features a ‘Filter’ drop-down menu offering a wide array of effects filters, many of them based upon traditional photographic filters. There are various ways of classifying filters, with respect to the effect they have on the incident radiation – (a) selectively by wavelength, as with color filters (b)nonselectively by wavelength, as with neutral density filters; or (c)selectively by angle of polarization, as with polarizing filters PHOTOGRAPHIC FILTERS Types of Filters: 1.) Color Correction – 85 and 80A These filters allow you to shoot daylight film under tungsten lighting, and tungsten film in a daylight situation. They adjust for the different color temperatures of the light source. They are an essential tool for wedding photographers who often find themselves shooting candle – lit scenes in a church to outside Shots of the bride and groom leaving the church. A major use is to compensate the effects of lighting not balanced for the film stock’s rated color temperature (usually 3200 K for professional tungsten lights and 5500 K for daylight): e.g., the 80A blue filter used with daylight film corrects the orange/reddish cast of household tungsten lighting, while the 85B 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. The use of these filters has been greatly reduced by the widespread adoption of digital photography, since the color balance problems are now often addressed with software after the image is captured. PHOTOGRAPHIC FILTERS 2.) Special Effects – kaleidoscope, graduated, textures, stars. Several companies make special effects filters and you should have a variety to choose from. Star filters work with all kinds of spectral highlights and create all kinds of stars. Some are soft-focus and some are not. Texture Filters can add painterly, artistic effects to your images. One of the most popular filters is the “star effect” filter. Technically it is referred to as a cross-screen filter because it consists of a linear grid pattern at which stars are created at light spots which produce attractive effects on a dark surrounding field of the light spots. This arrangement of thin wire lines embedded in a grid pattern is also known as a diffraction grating. The stars largely have the same color as the light source, but can also have spectral colors. The ray direction is always at right angles to the extent of the lines. Rotary mounts permit optimum alignment in the viewfinder of a reflex camera or on the monitor of a digital camera. Some filter manufacturers also use prisms in the filter (kaleidoscope effect). The number of stars varies by the construction of the filter, as does the number of points each star has, allowing them to create filters called: The North star, The Hollywood star, The Six-Point star, The Four Point Star, The Christmas Star, etc. PHOTOGRAPHIC FILTERS Graduated filters are preferably used for the coloring or darkening mostly of the sky or sometimes of the foreground. The rotatable mount permits the exact upward or downward alignment with the color or gray shade when the filter is screwed tight. If the sky is too bright with only low cloud delineation, the graduated gray filter or blue filter might work well. They are available in different values and graduations and you can choose how dramatic a look you want to create. Other graduated filters, such as the orange or red can produce a very dramatic sundown effect. The violet graduated filter creates a moonlight effect, and the paler lilac generates a ghost-like moonlight. The tobacco graduated filter produces a warming effect, similar to the feeling of the light before a sandstorm in the desert. The green or yellow-green graduated filters are usually used with the color portion of the lower half of the image to intensify the green of vegetation, possibly also in conjunction with a second graduated filter for the sky which otherwise could be overexposed. 3.) Soft focus / diffusion / softening / fog – Make your own by using hairspray and a clear glass filter ( UV ). Soft focus filters come in sets with different gradations and are an essential tool when photographing portraits, beauty or cosmetics ads. Fog and mist filters can create mood in your images. Soft focus filters give photos a delicate haze of gentle softness without loss of sharpness. They are popular for romantic portraits of girls or women, especially because they also hide wrinkles or skin blemishes. Good soft-focus attachments actually image light points in a sharp manner, surrounded by a distinct “halo”. Even sharpness fanatics can be won over by pictures taken with such highquality filters. Different optical manufacturing companies have come up with their own innovative designs for these filters. Zeiss Softars (steps 1, 2, 3) are made of optically high-quality plastic, which produces a slightly more pronounced soft focus. The B+W Soft Image filters produces a slightly subtler soft focus. Fog filters have a different effect. The subject appears to be behind a fine, thin veil of mist. Fog filters create distinct halos around light sources and very bright areas. With any of these filters, a slight over-exposure can further increase the romantic effect. PHOTOGRAPHIC FILTERS 4.) UV / Skylight / Protection filters – These filters are used to protect the outside glass element of your lens and to filter out unwanted ultraviolet radiation from sunlight. Ultraviolet radiation can cause blur or – in color shots – blueness. The UV filter is ideal for photos in the mountains, by the sea or in areas with very clear air. Pictures become more brilliant, irritating blue haze is avoided and color reproduction remains neutral. This filter is also suitable for use as front lens protection. The recommended filter for digital cameras is the UV/IR blocking filter #486, B+W, a steep flanked interference filter which additionally blocks infrared and prevents blur and color cast with IR-sensitive CCDs. The skylight filter (B+W #KR 1.5) also blocks UV radiation and has a delicate, reddish yellow shade to counter the high blue portion in shadow caused by the sky’s light in color transparencies with a warmer picture hue. A clear glass protective filter (Clear 007) has an optically high-quality clear glass With an MR coat and serves only as protection for the front lens. PHOTOGRAPHIC FILTERS 5.) Contrast control – Use these filters to increase or reduce the contrast of your light. You can buy them without color correction or as warming filters. They can help enliven a static landscape scene and add drama to a sky and clouds. Contrast enhancement filters are commonly used in black and white photography to manipulate contrast. 8.) Wratten 90 – allows the photographer to view the scene in b/w (gray scale) 6.) Neutral Density – One of the most useful filters you can own, the neutral density filter absorbs light to permit proper (usually longer) exposure without affecting the color. They are available in a number of different densities, steps, and you usually lose 2 to 3 stops with them. They are available in 1, 2, 3, 6 and 10 f-stops values. They permit the use of a wide aperture even when it is very bright for low depth-of-field and an interplay of sharpness and blur and/or long exposures for creating motion blur (i.e. - the flow of water). They also permit “normal” time values and f-stop values when the film sensitivity is too high for the prevailing light. Gray filters with higher density (3 to 10 f-stops ) are also used for technical photography, e.g. shots of light filaments, of combustion processes and procedures in melting ovens as well as for astrophotography. Neutral density filters can also be used over studio lights also when you are unable to decrease the intensity of the light by moving it back or dialing down the power, but still want to be able to open up your lens and shoot at a wider-open f-stop. PHOTOGRAPHIC FILTERS 7.) Black & White conversion – These filters convert a color scene to black & white. 9.) Color filters – allow only apparent visible wavelength of light 10.) Heat absorption – for hot lights – film and video 11.) Polarizing filters – These filters are unique, expensive and an essential photographic tool. They are effective at reducing glare on most surfaces, at a cost of about 2 1/3 stops. Greater glare control can be achieved if polarizing gels are also used on the lights, but this takes an additional 2 stops away. Polarizing filters darken skies and bring out the clouds. They can eliminate reflections from water, windows, windshields, glass of all types and any reflective surface. They need to be turned only ¼ stop. Polarizing filters do not affect the color, although warm-tone polarizers are also available. What is Polarized Light? Light is typically emitted in all directions and with different orientations; that is to say that a light wave may be oriented with the electric component of the electromagnetic wave vibrating up and down (vertically), while in other instances the light wave may vibrate horizontally or even diagonally. Regardless of the orientation, these light waves are not polarized. To be polarized, all the light waves must be oriented in the same direction. For example, vertically polarized light must have all its waves aligned in up and down vibrations. Non-polarized light produces glare, which can be a distraction when driving, skiing or taking pictures. How does light become polarized? Sunlight and most other sources of light are emitted in an assortment of orientations and are non-polarized. To reduce glare, a polarizing filter is used to accept only one orientation. For example, if you want to accept only vertically polarized light, then a polarizing filter with a vertical grating is used to allow all vertical vibrations to pass through, but prevents non-vertical light waves from entering. How can you check to make sure a pair of sunglasses are polarized? Polarized lenses mean that they are only transparent to light that is aligned in one direction. Therefore, if a pair of sunglasses claim to be polarized, two pairs of the same sunglasses, when set up perpendicular to each other should not allow any light to pass through the lenses. By aligning the lenses on top of each other and rotating them 90 degrees from each other, the polarized gratings eliminate all orientations of light and therefore prove that the sunglasses are indeed polarized. In addition, light from the sky is also polarized due to the scattering of light and gas molecules in the atmosphere, so if you put on a pair of polarized sunglasses and tilt your head so that your ear was near your shoulder, you should see a change in the intensity of the sky on a clear, sunny day. If you see no such change, then the sunglasses are not polarized. Normal scene, no polarizer Polarizer filter added PHOTOGRAPHIC FILTERS 12.) Close-up Filters – Close-up filters are used to photograph very small subjects and come in steps, just like diopters. They severely limit your depth of field, and make focusing difficult, but are much less expensive than close-up lenses. Most close-up filter sets come with a +1, +2 and a +3 filter.