تويت
التصوير الفوتوغرافي الحديث
التصوير بالألوان وحقائق حول المرشحات
الجزء الثاني حقائق حول المرشحات
فلاتر للتصوير الملون
FILTERS FOR COLOR PHOTOGRAPHY
As we have stated earlier in the Assignment , what is focused on the retina of the eye is not necessarily what we see . The brain interprets that image on the basis of our previous experience and tells us what we should see . Often there is a good deal of accommodation or eye adjustment in the process . For example , daylight looks white to us . If we switch on the tungsten lamp during the day , its light looks noticeably orange in comparison . At night , however , when there is no daylight to serve as a basis of comparison , the tungsten illumination looks white . Color film has no such power of accommodation . If it is designed or balanced to make daylight appear white , anything photographed under tungsten illumination will have an orange overcast . Conversely , if film is balanced for tungsten illumination , anything photographed in daylight will have a strong bluish cast .
This condition can be corrected through the use of color filters . A very light bluish filter , for example , will filter out enough red to permit daylight type color film to be used with tungsten illumination ; a light , salmon colored filter will permit indoor type color film to be used in daylight .
Filters for color photography are intended primarily to balance the film for a specific kind of light for which it was not designed . Such filters are quite pale in hue and have very little effect on picture contrast . There are two general types of light balancing filters for color work : the conversion filters and the color compensating or CC filters .
CONVERSION FILTERS . Conversion filters , as their name implies , are intended primarily to convert film to use with another type of light than the light for which it was balanced . For example , daylight type film can be converted to tungsten type with a suitable conversion filter . Tungsten type film can be converted to daylight film by another conversion filter . Filters which convert . daylight film for use with tungsten light are a light blue in color and are the cooling filters ; those which convert tungsten type film to daylight are either pale yellow or pale salmon and are the warming filters .
Table VII , page 40 , shows the Wratten ( made by Kodak ) filters in most com mon use . Other filter manufacturers may use their own numbers , but your dealer should be able to give you the equivalent Wratten number . Color films change from time to time . When choosing a conversion filter , therefore , it is advisable to follow the specific recommendations of the manufacturer whose film you use and check from time to time to see that these recommendations have not changed . One point to remember is that you get best results if you use the correct film for the light and do not rely on filters for correction . Not only do you get more accu rate color , but you usually gain speed because there is no filter factor to consider .
Not all tungsten illumination has the same color . The color of the light depends on the temperature of the filament ; the hotter the filament , the bluer the color . Note that in this use , the blue or cool color is actually the hotter filament .
The relation between the temperature of a lamp filament and the color of light it emits is very stable . For any specific temperature , the light will have a definite color balance from red to blue , including all the colors in between . So stable this relationship , that it is possible simply to state the temperature of the filament to establish the exact color of the light it emits . The scale of temperatures used is the Kelvin rather than the more familiar Fahrenheit or Centigrade scale . The Kelvin scale is the most scientific and is based on absolute temperature .
A standard 100 watt tungsten filament lamp operates at a temperature of about 2860 ° Kelvin ( usually abbreviated to 2860 ° K. ) . A photoflood lamp filament operates at about 3400 ° K. , and a blue flashbulb at 6000 ° K. A common type of tungsten lamp designed for color photography has a filament temperature of 3200 ° K. This provides more light per watt than an ordinary tungsten lamp , yet gives longer life than a photoflood lamp .
Type A color film is balanced to 3400 ° K. ( photoflood ) illumination . Type B color film is balanced to 3200 ° K. light . If artificial light of any other color temperature is to be used with either type of film , a suitable conversion or color compensating filter must be used . It is best to get filter recommendations for such conversions from the film manufacturer , since this is subject to change without notice .
COLOR COMPENSATING ( CC ) FILTERS . These filters are used for extremely precise color work either when making the original exposure or when making color prints . They are provided in six colors - red , green , blue ( the primary colors ) . and yellow , magenta , cyan ( the complementary colors ) . Each color is available in a series of accurately controlled densities , and the densities of each filter have a definite relationship to each other . The number of any CC filter indicates its color and its density . For example , a CC 10 Y filter is a yellow color compensating filter having a peak density of 10 ..
POLARIZING FILTERS FOR COLOR PHOTOGRAPHY . The blue light reflected to us from the sky is polarized light . It is , therefore , affected by a polarizing filter . As a matter of fact , a polarizing filter is the only method of getting a dark sky in color photography without greatly altering the colors . Maximum darkening of the sky is obtained when the indicator on the filter is pointed as closely as possible in the direction of the sun .
To obtain the most striking effects with a polarizing filter , the sky should be quite clear . Haze breaks up the polarized light from the sky and cancels out much of its polarized nature .
Polarizing filters have another useful function in color photography . Technically stated , they tend to increase color saturation . This means that colors tend to be photographed with greater brightness and contrast . If a polarizing filter is used at the correct angle , the resulting darkening of the sky and increasing brilliance of the colors may be quite dramatic .
HAZE AND SKYLIGHT FILTERS . Color photographs show up atmospheric haze strongly , often to the detriment of the picture . Distant landscapes , particularly in mountain areas , may under these circumstances have an excessively bluish cast . Haze filters for color film have very light yellowish colors and warm up the scene just enough to kill the excessive blue tinge . Haze filters for color film cannot actually penetrate the haze because their colors cannot be dark enough for that .
The skylight filter is somewhat stronger in color and will produce a more noticeable warming effect . It is also useful in getting rid of the blue overcast obtained when taking color pictures in the shade with blue sky as the sole source of light .
Note : The above filter factors are necessarily approximate since the color sensitivity of film varies from brand to brand .
التصوير بالألوان وحقائق حول المرشحات
الجزء الثاني حقائق حول المرشحات
فلاتر للتصوير الملون
FILTERS FOR COLOR PHOTOGRAPHY
As we have stated earlier in the Assignment , what is focused on the retina of the eye is not necessarily what we see . The brain interprets that image on the basis of our previous experience and tells us what we should see . Often there is a good deal of accommodation or eye adjustment in the process . For example , daylight looks white to us . If we switch on the tungsten lamp during the day , its light looks noticeably orange in comparison . At night , however , when there is no daylight to serve as a basis of comparison , the tungsten illumination looks white . Color film has no such power of accommodation . If it is designed or balanced to make daylight appear white , anything photographed under tungsten illumination will have an orange overcast . Conversely , if film is balanced for tungsten illumination , anything photographed in daylight will have a strong bluish cast .
This condition can be corrected through the use of color filters . A very light bluish filter , for example , will filter out enough red to permit daylight type color film to be used with tungsten illumination ; a light , salmon colored filter will permit indoor type color film to be used in daylight .
Filters for color photography are intended primarily to balance the film for a specific kind of light for which it was not designed . Such filters are quite pale in hue and have very little effect on picture contrast . There are two general types of light balancing filters for color work : the conversion filters and the color compensating or CC filters .
CONVERSION FILTERS . Conversion filters , as their name implies , are intended primarily to convert film to use with another type of light than the light for which it was balanced . For example , daylight type film can be converted to tungsten type with a suitable conversion filter . Tungsten type film can be converted to daylight film by another conversion filter . Filters which convert . daylight film for use with tungsten light are a light blue in color and are the cooling filters ; those which convert tungsten type film to daylight are either pale yellow or pale salmon and are the warming filters .
Table VII , page 40 , shows the Wratten ( made by Kodak ) filters in most com mon use . Other filter manufacturers may use their own numbers , but your dealer should be able to give you the equivalent Wratten number . Color films change from time to time . When choosing a conversion filter , therefore , it is advisable to follow the specific recommendations of the manufacturer whose film you use and check from time to time to see that these recommendations have not changed . One point to remember is that you get best results if you use the correct film for the light and do not rely on filters for correction . Not only do you get more accu rate color , but you usually gain speed because there is no filter factor to consider .
Not all tungsten illumination has the same color . The color of the light depends on the temperature of the filament ; the hotter the filament , the bluer the color . Note that in this use , the blue or cool color is actually the hotter filament .
The relation between the temperature of a lamp filament and the color of light it emits is very stable . For any specific temperature , the light will have a definite color balance from red to blue , including all the colors in between . So stable this relationship , that it is possible simply to state the temperature of the filament to establish the exact color of the light it emits . The scale of temperatures used is the Kelvin rather than the more familiar Fahrenheit or Centigrade scale . The Kelvin scale is the most scientific and is based on absolute temperature .
A standard 100 watt tungsten filament lamp operates at a temperature of about 2860 ° Kelvin ( usually abbreviated to 2860 ° K. ) . A photoflood lamp filament operates at about 3400 ° K. , and a blue flashbulb at 6000 ° K. A common type of tungsten lamp designed for color photography has a filament temperature of 3200 ° K. This provides more light per watt than an ordinary tungsten lamp , yet gives longer life than a photoflood lamp .
Type A color film is balanced to 3400 ° K. ( photoflood ) illumination . Type B color film is balanced to 3200 ° K. light . If artificial light of any other color temperature is to be used with either type of film , a suitable conversion or color compensating filter must be used . It is best to get filter recommendations for such conversions from the film manufacturer , since this is subject to change without notice .
COLOR COMPENSATING ( CC ) FILTERS . These filters are used for extremely precise color work either when making the original exposure or when making color prints . They are provided in six colors - red , green , blue ( the primary colors ) . and yellow , magenta , cyan ( the complementary colors ) . Each color is available in a series of accurately controlled densities , and the densities of each filter have a definite relationship to each other . The number of any CC filter indicates its color and its density . For example , a CC 10 Y filter is a yellow color compensating filter having a peak density of 10 ..
POLARIZING FILTERS FOR COLOR PHOTOGRAPHY . The blue light reflected to us from the sky is polarized light . It is , therefore , affected by a polarizing filter . As a matter of fact , a polarizing filter is the only method of getting a dark sky in color photography without greatly altering the colors . Maximum darkening of the sky is obtained when the indicator on the filter is pointed as closely as possible in the direction of the sun .
To obtain the most striking effects with a polarizing filter , the sky should be quite clear . Haze breaks up the polarized light from the sky and cancels out much of its polarized nature .
Polarizing filters have another useful function in color photography . Technically stated , they tend to increase color saturation . This means that colors tend to be photographed with greater brightness and contrast . If a polarizing filter is used at the correct angle , the resulting darkening of the sky and increasing brilliance of the colors may be quite dramatic .
HAZE AND SKYLIGHT FILTERS . Color photographs show up atmospheric haze strongly , often to the detriment of the picture . Distant landscapes , particularly in mountain areas , may under these circumstances have an excessively bluish cast . Haze filters for color film have very light yellowish colors and warm up the scene just enough to kill the excessive blue tinge . Haze filters for color film cannot actually penetrate the haze because their colors cannot be dark enough for that .
The skylight filter is somewhat stronger in color and will produce a more noticeable warming effect . It is also useful in getting rid of the blue overcast obtained when taking color pictures in the shade with blue sky as the sole source of light .
Note : The above filter factors are necessarily approximate since the color sensitivity of film varies from brand to brand .
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