تويت
التصوير الفوتوغرافي الحديث
تحديد الوضع الصحيح ..
تحديد التعرض الناجح ..
التعرض الناجح ..
DETERMINING THE RIGHT EXPOSURE
The basis of photography is the controlled exposure of light - sensitive film . In this Assignment you are going to learn just what makes a successfully controlled exposure and why . You will come to understand why the brightness of the subject , the intensity of light , the speed of the lens , and the speed of the film all have an important bearing on exposure .
Special coverage will be devoted to the characteristics of films important in black - and - white photography . The classifications of film based on color sensitivity , speed , and application will also be explored .
SUCCESSFUL EXPOSURE
Correct exposure is fundamental . It is the basis upon which all successful photography rests . Because of this , it is vital that you have a clear and thorough understanding of this important subject . First of all , let us see why you must expose correctly - why , for example , you cannot simply open the shutter and close it whenever you choose . Why must exposure time be so carefully determined ?
To answer this question , let us deal briefly with the nature of the light - sensitive material we use in our cameras . Photographic film consists of a sheet of completely transparent plastic , one side of which is coated with a thin layer of gelatin containing very finely divided silver salts - predominantly silver bromide . When light strikes the tiny grains of silver bromide , it produces a chemical reaction in them , which makes them release tiny amounts of the metall silver . When the film is processed , more silver is built on the silver particles released by the action of the light , and the unexposed particles of silver bromide are then dissolved and washed away . This leaves a dark image where light struck the film , and clear plastic where the particles were washed away .
A certain minimum amount of light is needed to produce this chemical action in every silver bromide particle . This means that nothing happens until the amount of light reaches a certain strength . The silver bromide grains are not equally sensitive - to be acted upon , some require much more light than others . Therefore , as the exposure is increased , more and more silver bromide grains are acted upon until there are enough to form a strong image when developed . If we don't give the film enough exposure , most of the silver bromide will not react to the light and will , therefore , be dissolved away during processing . This will leave us with a light , transparent , underexposed negative that will produce a dark print . On the other we continue to expose the film , more and more of the silver bromide particles react to the light until almost all of them become converted to silver . This results in a dark , opaque , overexposed negative , which has very little difference in tonal values , producing a very light print .
So you can see how important it is that exposure lasts just the right amount of time . If we don't have enough exposure , we produce a dark print with little visible detail . If we have too much exposure , we produce a picture that is lifeless , with very little difference among the tones in the lighter areas .
To illustrate : visualize a portrait of a girl , with fairly dark hair , wearing a white dress . The light is arranged to produce some interesting shadows along one side of the nose and under the chin . Let us give this subject a very short exposure and see what happens . To begin with , only a small amount of light is reflected to the camera from the girl's dark hair and from the shadows on her face . If the exposure is too short , we get no image at all from these areas . The developed negative will be clear in the hair and face shadows , and the print will show them as solid black with no detail . Her face and dress , being much lighter may reflect enough light so they will come out fairly well . Obviously , we must increase exposure to get a good portrait .
Now let us see what happens if we increase exposure too much . The amount of light reflected from the girl's face will expose nearly all the silver bromide particles on the film and make it almost completely black after development . When the negative is printed , her face comes out practically a uniform white . The white dress the girl is wearing , even though it is much brighter than her face , cannot produce much more reaction in the film and so it also appears completely white . If there are any attractive highlights or shiny surfaces on the subject's face , they are lost because they cannot be any whiter than the already white face . In other words , by overexposing our film , we have lost all our delicate highlights and the detail that would have been shown by a variety of tones in the lighter parts of the subject .
تحديد الوضع الصحيح ..
تحديد التعرض الناجح ..
التعرض الناجح ..
DETERMINING THE RIGHT EXPOSURE
The basis of photography is the controlled exposure of light - sensitive film . In this Assignment you are going to learn just what makes a successfully controlled exposure and why . You will come to understand why the brightness of the subject , the intensity of light , the speed of the lens , and the speed of the film all have an important bearing on exposure .
Special coverage will be devoted to the characteristics of films important in black - and - white photography . The classifications of film based on color sensitivity , speed , and application will also be explored .
SUCCESSFUL EXPOSURE
Correct exposure is fundamental . It is the basis upon which all successful photography rests . Because of this , it is vital that you have a clear and thorough understanding of this important subject . First of all , let us see why you must expose correctly - why , for example , you cannot simply open the shutter and close it whenever you choose . Why must exposure time be so carefully determined ?
To answer this question , let us deal briefly with the nature of the light - sensitive material we use in our cameras . Photographic film consists of a sheet of completely transparent plastic , one side of which is coated with a thin layer of gelatin containing very finely divided silver salts - predominantly silver bromide . When light strikes the tiny grains of silver bromide , it produces a chemical reaction in them , which makes them release tiny amounts of the metall silver . When the film is processed , more silver is built on the silver particles released by the action of the light , and the unexposed particles of silver bromide are then dissolved and washed away . This leaves a dark image where light struck the film , and clear plastic where the particles were washed away .
A certain minimum amount of light is needed to produce this chemical action in every silver bromide particle . This means that nothing happens until the amount of light reaches a certain strength . The silver bromide grains are not equally sensitive - to be acted upon , some require much more light than others . Therefore , as the exposure is increased , more and more silver bromide grains are acted upon until there are enough to form a strong image when developed . If we don't give the film enough exposure , most of the silver bromide will not react to the light and will , therefore , be dissolved away during processing . This will leave us with a light , transparent , underexposed negative that will produce a dark print . On the other we continue to expose the film , more and more of the silver bromide particles react to the light until almost all of them become converted to silver . This results in a dark , opaque , overexposed negative , which has very little difference in tonal values , producing a very light print .
So you can see how important it is that exposure lasts just the right amount of time . If we don't have enough exposure , we produce a dark print with little visible detail . If we have too much exposure , we produce a picture that is lifeless , with very little difference among the tones in the lighter areas .
To illustrate : visualize a portrait of a girl , with fairly dark hair , wearing a white dress . The light is arranged to produce some interesting shadows along one side of the nose and under the chin . Let us give this subject a very short exposure and see what happens . To begin with , only a small amount of light is reflected to the camera from the girl's dark hair and from the shadows on her face . If the exposure is too short , we get no image at all from these areas . The developed negative will be clear in the hair and face shadows , and the print will show them as solid black with no detail . Her face and dress , being much lighter may reflect enough light so they will come out fairly well . Obviously , we must increase exposure to get a good portrait .
Now let us see what happens if we increase exposure too much . The amount of light reflected from the girl's face will expose nearly all the silver bromide particles on the film and make it almost completely black after development . When the negative is printed , her face comes out practically a uniform white . The white dress the girl is wearing , even though it is much brighter than her face , cannot produce much more reaction in the film and so it also appears completely white . If there are any attractive highlights or shiny surfaces on the subject's face , they are lost because they cannot be any whiter than the already white face . In other words , by overexposing our film , we have lost all our delicate highlights and the detail that would have been shown by a variety of tones in the lighter parts of the subject .
تعليق