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مرشحات الألوان - ١ - مصدر الضوء .. كيفية التقاط وتطوير الصور الملونة
FILTERS FOR COLOUR
Filters that fit over the lens are a key method of controlling the colour and tone of your images . The important filters are not , however , the special effects and trick filters that produce rainbows , stars and drastic colour changes . Although these can sometimes be fun to experiment with , the filters for serious use are those that balance the light , compensate for shifts , cut parts of the spectrum and alter contrast . Few photographers maintain a full set , but it is as well to know which filter will do what .
LIGHT BALANCING FILTERS
- This range of filters is used to match the film to the light . We have already seen why this is necessary in selecting daylight or tungsten - balanced film . However , you may often find yourself with the wrong film for the light source ; for instance , if you have been using regular daylight film but suddenly find an opportunity for an indoor picture . In this case , there is a blue filter to balance the light 80A in the Kodak series ( there are equivalent filters from other manufacturers , with different designations ) . The opposite filter , for using Type B film in daylight , is an 85B . These two filters are the strongest that are normally used , but a whole range of weaker filters is available for making slight corrections . One of the commonest uses is on an overcast day , when the overall colour balance is a little cool . To warm up the image , many photographers use an 81 , 81A or 81C filter . These are straw - coloured and give just a hint of warmth . Indoors , using available domestic tungsten lighting , cooling correc- tion may be needed , as the colour temperature of these lamps is lower than the 3200K of type B film .
COLOUR COMPENSATION FILTERS
These filters are for correcting colour shifts the kind that may be due to differences in film manufacture , reciprocity failure or to some artificial light sources such as fluorescent and vapour lamps . They are available in six basic colours : red , blue , green , cyan , yellow and magenta . There are different strengths for each , and in the right combination , any colour can be created .
A polarizing filter was used for the shot above , which cut out the reflection from the surface of the water ; but the effect is unsatisfactory because of the lack of light altogether . The shot without the filter ( top ) is probably better . Filters will not solve every problem .
BELOW AND BELOW LEFT Ultra violet light can make distant haze appear bluish . A UV filter can correct this .
ULTRAVIOLET FILTERS
These plain , or slightly yellowish , filters are designed to cut the response of film to invisible UV wavelengths . These wavelengths make distant haze appear bluish and add a blue cast to pictures taken on mountains . Improvements in recent years in film has made UV filters less dramatic in their effect on colour film , but still useful ( they also protect the front of the lens ) .
POLARIZING FILTERS
Daylight is partly polarized , which means that it vibrates in only one plane Although this effect is normally invisible , it can be used by means of a polariz- ing filter , which allows light through in just one plane . If the plane of the daylight and that of the filter are lined up , there is no effect , but if the filter is rotated , it quenches the polarized light . In practice , this affects reflections from anything except metal , and the most obvious effects are when photographing water or glass . If the camera view is at about 35 degrees , the surface reflections will virtually disappear . And , as the blue of a clear sky is caused by light being reflected off minute particles in the atmosphere , the blue is intensified by the filter . This sky - darkening is strongest at right angles to the sun , and weakest in
ABOVE Since the blue of a clear sky is caused by light being reflected off tiny particles in the atmosphere , that blue can be deepened with the use of a polarizing filter .
How Filters Work
These diagrams ( below ) show how coloured filters subtract from basic white light . The three filters are of the complementary colours , yellow , magenta and cyan . The yellow filter blocks the path of blue light rays , allowing red and green to pass unhindered . In the same way the magenta filter blocks green light rays , and the cyan filter blocks red . When all three filters are combined together no light at all is allowed through , and the result is black .
The two sets of circles ( right ) show the two ways of creating colours photographically . The three primary colours - blue , red and green - when mixed equally , create white . In combinations of two they create complementary colours - blue and red make magenta , green and red make yellow , and blue and green make cyan . This is the additive process . In the subtractive process , complementary colours subtract from white light to produce the primary colours and black .
the direction of the sun , directly away from it , and close to the horizon . An especially useful application of polarizing filters is in cutting haze in a distant view ; they are much more effective than a UV filter . Polarizing filters absorb quite a lot of light , and the price to pay for using one is that you will need to adjust the exposure by about 1½ stops . A TTL meter automatically makes this compensation .
FILTERS FOR COLOUR
Filters that fit over the lens are a key method of controlling the colour and tone of your images . The important filters are not , however , the special effects and trick filters that produce rainbows , stars and drastic colour changes . Although these can sometimes be fun to experiment with , the filters for serious use are those that balance the light , compensate for shifts , cut parts of the spectrum and alter contrast . Few photographers maintain a full set , but it is as well to know which filter will do what .
LIGHT BALANCING FILTERS
- This range of filters is used to match the film to the light . We have already seen why this is necessary in selecting daylight or tungsten - balanced film . However , you may often find yourself with the wrong film for the light source ; for instance , if you have been using regular daylight film but suddenly find an opportunity for an indoor picture . In this case , there is a blue filter to balance the light 80A in the Kodak series ( there are equivalent filters from other manufacturers , with different designations ) . The opposite filter , for using Type B film in daylight , is an 85B . These two filters are the strongest that are normally used , but a whole range of weaker filters is available for making slight corrections . One of the commonest uses is on an overcast day , when the overall colour balance is a little cool . To warm up the image , many photographers use an 81 , 81A or 81C filter . These are straw - coloured and give just a hint of warmth . Indoors , using available domestic tungsten lighting , cooling correc- tion may be needed , as the colour temperature of these lamps is lower than the 3200K of type B film .
COLOUR COMPENSATION FILTERS
These filters are for correcting colour shifts the kind that may be due to differences in film manufacture , reciprocity failure or to some artificial light sources such as fluorescent and vapour lamps . They are available in six basic colours : red , blue , green , cyan , yellow and magenta . There are different strengths for each , and in the right combination , any colour can be created .
A polarizing filter was used for the shot above , which cut out the reflection from the surface of the water ; but the effect is unsatisfactory because of the lack of light altogether . The shot without the filter ( top ) is probably better . Filters will not solve every problem .
BELOW AND BELOW LEFT Ultra violet light can make distant haze appear bluish . A UV filter can correct this .
ULTRAVIOLET FILTERS
These plain , or slightly yellowish , filters are designed to cut the response of film to invisible UV wavelengths . These wavelengths make distant haze appear bluish and add a blue cast to pictures taken on mountains . Improvements in recent years in film has made UV filters less dramatic in their effect on colour film , but still useful ( they also protect the front of the lens ) .
POLARIZING FILTERS
Daylight is partly polarized , which means that it vibrates in only one plane Although this effect is normally invisible , it can be used by means of a polariz- ing filter , which allows light through in just one plane . If the plane of the daylight and that of the filter are lined up , there is no effect , but if the filter is rotated , it quenches the polarized light . In practice , this affects reflections from anything except metal , and the most obvious effects are when photographing water or glass . If the camera view is at about 35 degrees , the surface reflections will virtually disappear . And , as the blue of a clear sky is caused by light being reflected off minute particles in the atmosphere , the blue is intensified by the filter . This sky - darkening is strongest at right angles to the sun , and weakest in
ABOVE Since the blue of a clear sky is caused by light being reflected off tiny particles in the atmosphere , that blue can be deepened with the use of a polarizing filter .
How Filters Work
These diagrams ( below ) show how coloured filters subtract from basic white light . The three filters are of the complementary colours , yellow , magenta and cyan . The yellow filter blocks the path of blue light rays , allowing red and green to pass unhindered . In the same way the magenta filter blocks green light rays , and the cyan filter blocks red . When all three filters are combined together no light at all is allowed through , and the result is black .
The two sets of circles ( right ) show the two ways of creating colours photographically . The three primary colours - blue , red and green - when mixed equally , create white . In combinations of two they create complementary colours - blue and red make magenta , green and red make yellow , and blue and green make cyan . This is the additive process . In the subtractive process , complementary colours subtract from white light to produce the primary colours and black .
the direction of the sun , directly away from it , and close to the horizon . An especially useful application of polarizing filters is in cutting haze in a distant view ; they are much more effective than a UV filter . Polarizing filters absorb quite a lot of light , and the price to pay for using one is that you will need to adjust the exposure by about 1½ stops . A TTL meter automatically makes this compensation .
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