تويت
التصوير الفوتوغرافي الحديث
التصوير بالألوان وحقائق حول المرشحات
حقائق الجزء الثاني عن المرشحات
مرشحات الألوان للتصوير الأسود والأبيض
Part II Facts About Filters
All ordinary objects reflect light to a greater or lesser degree . If an object reflects all colors approximately equally , it has no color of its own . It looks white . If it absorbs some of the light but the reflected light is still composed of approximately equal proportions of all colors , the object looks gray . If it reflects very little or no light at all , it appears black .
If an object does not reflect all colors equally , we see it as a colored object . The color we see is the color it reflects . For example , if a flower reflects all the red light striking it and absorbs all other colors , only red light comes to our eyes when we look at it . Therefore , the flower looks red .
In the same way , if we look through a piece of completely transparent glass , we see all objects in their true colors . Suppose we have a piece of glass that lets only red light through , but absorbs and stops all other colors . White objects seen through such a piece of glass appear red because we see only the red light coming from these objects . The glass itself also looks red .
A color filter , as used in photography , is a sheet of glass , gelatin , or other transparent medium that is colored for the purpose of absorbing light of certain colors .
In any discussion of filters , we must be very careful to keep in mind the type of film with which the filters are to be used . Color photography and black - and - white photography impose very different requirements . You can be badly confused and misled if you apply filter principles for black - and - white photography to filters used for color photography . For that reason we will divide this section into two parts , the use of color filters in black - and - white photography , and the use of filters in color photography . Be sure to keep this distinction in mind .
COLOR FILTERS FOR BLACK - AND - WHITE PHOTOGRAPHY
FILM SENSITIVITY
When we photograph a white object , all the colors of the spectrum are reflected from it and focused on the film to produce our picture . Actually , however , not all of these colors have an equally strong effect on the film
emulsion . The blue has the strongest effect , the red has less , or no effect at all , depending upon the type of film . As long as we are photographing a white object , these differences in the sensitivity of the film to different colors are not important . The effective sensitivity of the film is simply the sum of its sensitivities to all colors . However , when we photograph colored objects on black - and - white film , we must take into account this variation in sensitivity to the different colors .
Let us suppose we photograph an outdoor scene containing a blue sky . Since the photographic emulsion is very sensitive to blue , the negative of the sky becomes darker , and the print of the sky lighter than it should . It would photograph so light , as a matter of fact , that if the film is somewhat overexposed , the sky would come out completely white in the print . Any clouds in the sky would be lost because they , too , would be white .
It so happens that the eye is also not equally responsive to all colors of the spectrum . To the eye , blue is a fairly dark color , whereas to the film it is a light color . Greenish - yellow , on the other hand , is a very bright color to the eye , but only moderately bright to the film . Red is a moderately dark color to the eye . To the ordinary panchromatic film , red appears about as it does to the eye ; to many super - sensitive panchromatic emulsions , however , it appears somewhat lighter than it does to the eye .
These differences may or may not be important , depending upon individual circumstances . In most cases , slight variations in tone of colored objects are not even noticed . It is generally of little consequence whether the green grass in an outdoor scene is a little lighter or a little darker than it appeared to the eye at the time the picture was made . In an outdoor snapshot , if a blue skirt photographs a little lighter than it actually is , and a bright green sweater a little darker , who is to notice or to care ? Remember we are discussing black - and - white pictures where these slight differences come through only as slightly different shades of gray and not as colors .
There are times when it is important to have an accurate representation of the brightness values of all colors . For example , if a client asks a commercial photographer to photograph some of his merchandise , he expects that the finished photograph will show all the colors in their correct relative values . If a light blue area on his product comes through lighter than , let us say , a bright yellow , he will object because tone values have been distorted and his product has not been presented accurately .
To modify or change the relative value of colors as seen by the film , we use color filters .
FILTER ACTION
The action of a filter is to stop or absorb light of certain colors and to pass ( transmit ) light of other colors . That is all a color filter does and that is all it is expected to do . Notice that this definition does not apply to polarizing screens ,
such as the Polaroid filter or the Pola - Screen . The function of polarizing screens will be discussed later .
Because a filter absorbs certain colors selectively , it necessarily appears colored itself . As a red book appears red because it reflects red light and absorbs light of other so does a red filter appear red because it transmits red light and absorbs the other colors to a greater or lesser degree . Similarly , a filter which absorbs only blue appears yellow , because it transmits green and red , and these two colors in combination appear as yellow to the eye . As an example , the popular yellow Wratten K2 filter absorbs a certain amount of blue light without appreciably absorbing light of any other color .
التصوير بالألوان وحقائق حول المرشحات
حقائق الجزء الثاني عن المرشحات
مرشحات الألوان للتصوير الأسود والأبيض
Part II Facts About Filters
All ordinary objects reflect light to a greater or lesser degree . If an object reflects all colors approximately equally , it has no color of its own . It looks white . If it absorbs some of the light but the reflected light is still composed of approximately equal proportions of all colors , the object looks gray . If it reflects very little or no light at all , it appears black .
If an object does not reflect all colors equally , we see it as a colored object . The color we see is the color it reflects . For example , if a flower reflects all the red light striking it and absorbs all other colors , only red light comes to our eyes when we look at it . Therefore , the flower looks red .
In the same way , if we look through a piece of completely transparent glass , we see all objects in their true colors . Suppose we have a piece of glass that lets only red light through , but absorbs and stops all other colors . White objects seen through such a piece of glass appear red because we see only the red light coming from these objects . The glass itself also looks red .
A color filter , as used in photography , is a sheet of glass , gelatin , or other transparent medium that is colored for the purpose of absorbing light of certain colors .
In any discussion of filters , we must be very careful to keep in mind the type of film with which the filters are to be used . Color photography and black - and - white photography impose very different requirements . You can be badly confused and misled if you apply filter principles for black - and - white photography to filters used for color photography . For that reason we will divide this section into two parts , the use of color filters in black - and - white photography , and the use of filters in color photography . Be sure to keep this distinction in mind .
COLOR FILTERS FOR BLACK - AND - WHITE PHOTOGRAPHY
FILM SENSITIVITY
When we photograph a white object , all the colors of the spectrum are reflected from it and focused on the film to produce our picture . Actually , however , not all of these colors have an equally strong effect on the film
emulsion . The blue has the strongest effect , the red has less , or no effect at all , depending upon the type of film . As long as we are photographing a white object , these differences in the sensitivity of the film to different colors are not important . The effective sensitivity of the film is simply the sum of its sensitivities to all colors . However , when we photograph colored objects on black - and - white film , we must take into account this variation in sensitivity to the different colors .
Let us suppose we photograph an outdoor scene containing a blue sky . Since the photographic emulsion is very sensitive to blue , the negative of the sky becomes darker , and the print of the sky lighter than it should . It would photograph so light , as a matter of fact , that if the film is somewhat overexposed , the sky would come out completely white in the print . Any clouds in the sky would be lost because they , too , would be white .
It so happens that the eye is also not equally responsive to all colors of the spectrum . To the eye , blue is a fairly dark color , whereas to the film it is a light color . Greenish - yellow , on the other hand , is a very bright color to the eye , but only moderately bright to the film . Red is a moderately dark color to the eye . To the ordinary panchromatic film , red appears about as it does to the eye ; to many super - sensitive panchromatic emulsions , however , it appears somewhat lighter than it does to the eye .
These differences may or may not be important , depending upon individual circumstances . In most cases , slight variations in tone of colored objects are not even noticed . It is generally of little consequence whether the green grass in an outdoor scene is a little lighter or a little darker than it appeared to the eye at the time the picture was made . In an outdoor snapshot , if a blue skirt photographs a little lighter than it actually is , and a bright green sweater a little darker , who is to notice or to care ? Remember we are discussing black - and - white pictures where these slight differences come through only as slightly different shades of gray and not as colors .
There are times when it is important to have an accurate representation of the brightness values of all colors . For example , if a client asks a commercial photographer to photograph some of his merchandise , he expects that the finished photograph will show all the colors in their correct relative values . If a light blue area on his product comes through lighter than , let us say , a bright yellow , he will object because tone values have been distorted and his product has not been presented accurately .
To modify or change the relative value of colors as seen by the film , we use color filters .
FILTER ACTION
The action of a filter is to stop or absorb light of certain colors and to pass ( transmit ) light of other colors . That is all a color filter does and that is all it is expected to do . Notice that this definition does not apply to polarizing screens ,
such as the Polaroid filter or the Pola - Screen . The function of polarizing screens will be discussed later .
Because a filter absorbs certain colors selectively , it necessarily appears colored itself . As a red book appears red because it reflects red light and absorbs light of other so does a red filter appear red because it transmits red light and absorbs the other colors to a greater or lesser degree . Similarly , a filter which absorbs only blue appears yellow , because it transmits green and red , and these two colors in combination appear as yellow to the eye . As an example , the popular yellow Wratten K2 filter absorbs a certain amount of blue light without appreciably absorbing light of any other color .
تعليق