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تغيير جودة الفيلم .. المعالجة والطباعة .. كيفية التقاط وتطوير الصور بالأبيض والأسود
ALTERING FILM QUALITIES
Deliberate over- and under - exposure not only affect the density of the nega- tive , but the contrast also . This is a valuable technique for controlling the image and is , incidentally , an important part of using the Zone System described earlier . Because there are only tones to think about , altered development is a much simpler and more useful technique in black - and - white than it could ever be in colour .
If you increase the development , the tonal range is expanded , and so the contrast is increased . If , on the other hand , the development is decreased , the
If the aim is to reduce contrast from the average ( below ) , then the tonal range may be compressed by decreasing the development of the print ( left ) .
RIGHT If development of a print is increased , the tonali range is expanded , with the result that contrast is boosted .
Altering Film Development
Under - development lowers contrast and so extends the tonal range ( far right ) . Over - development increases contrast , compressing the tonal range . ( right ) . Therefore , with a high contrast subject , where bright highlights and dense shadows cannot both be recorded on a normally processed negative , under- developing the film ( by shortening the time or diluting the chemicals ) will help . To compensate , the exposure will have had to have been increased . On the other hand , if the subject is flat , increasing the development ( by extending the time , raising the temperature or increasing the concentration of developer ) will make the image more lively . In this case , the exposure must have been reduced . For this type of contrast control , adjustments in the order of a half or one f - stop are normally made .
tonal range is compressed and the contrast reduced . This means , for example , that a scene with a limited range of tones , such as on a dull day , can be given more life by push - processing the film . If you are using this technique only to control the contrast , remember to adjust the exposure setting accordingly . Should you plan to reduce contrast by under - developing one stop , for instance , the lens aperture will have to be opened up or the shutter speed slowed down by the equivalent amount . Alternatively , you could alter the film speed rating : for one - stop underdevelopment of Tri - X or HP5 , rate them at ISO200 instead of ISO400 .
The actual procedure varies according to the film / developer combination , and there is even some choice . There are three things that affect the degree of development : the development time ; the temperature ; and the strength of the developer solution . In theory , changing any of these will do the job , but the limits are set by the need for an evenly processed image . Under - development in particular is limited by this , and for this reason it may be better to use a special low - contrast developer ; development times should be at least more than 5 minutes . Overall , the most commonly used technique is altering the time ( this is the only practical choice available to a professional lab , which is processing quantities of film at time most of it normal ) .
SPEED vs CONTRAST
Because altered processing changes both the strength and contrast of the image , it is important to be clear about the effect that you want . Push - proces- sing can be used as a technique for photographing in low light or for higher contrast , or for both . The film speed is adjustable , but the increase in contrast is inevitable , as is an increase in grain . In particular , the shadow areas ( those which receive least exposure and so are palest in the negative ) tend to lose detail , and block up into solid areas of black when the negative is printed . Graininess , as we saw earlier , becomes most obvious in mid - toned areas .
For maximum film speed , select a fast film to begin with , as push - processing a slow or medium film is always less effective than using a film that has been designed for its great sensitivity to light . On the other hand , if you want only to increase the contrast , it is more effective if you choose a slow film - this is already slightly more contrasty than faster emulsions .
Pull - processing is less commonly used , simply because of the circumstances in which most photographs are taken . There is insufficient light for photography more often than there is too much , and the requirement for high contrast in a scene is more usual than lowering it .
Although all of the above assumes that you have planned to change the development from the start , these are also useful emergency procedures in cases where you have made an exposure mistake . The most common is forget- ting to change the meter setting or film speed dial when changing film types . If this happens , simply continue shooting at the ' wrong ' setting ( provided that it is within a correctable range , between about 2 stops under and 3 stops over ) , and make the adjustments to the development .
Under - development gives low contrast ( above ) , over- development gives high ( above right ) . The second shot had been under - exposed to allow for over - development .
ABOVE One by product of the increase in contrast that results from push processing is a loss of detail in shadow areas , which tend to block into solid black Graininess , meanwhile , becomes most obvious in mid toned areas .
ALTERING FILM QUALITIES
Deliberate over- and under - exposure not only affect the density of the nega- tive , but the contrast also . This is a valuable technique for controlling the image and is , incidentally , an important part of using the Zone System described earlier . Because there are only tones to think about , altered development is a much simpler and more useful technique in black - and - white than it could ever be in colour .
If you increase the development , the tonal range is expanded , and so the contrast is increased . If , on the other hand , the development is decreased , the
If the aim is to reduce contrast from the average ( below ) , then the tonal range may be compressed by decreasing the development of the print ( left ) .
RIGHT If development of a print is increased , the tonali range is expanded , with the result that contrast is boosted .
Altering Film Development
Under - development lowers contrast and so extends the tonal range ( far right ) . Over - development increases contrast , compressing the tonal range . ( right ) . Therefore , with a high contrast subject , where bright highlights and dense shadows cannot both be recorded on a normally processed negative , under- developing the film ( by shortening the time or diluting the chemicals ) will help . To compensate , the exposure will have had to have been increased . On the other hand , if the subject is flat , increasing the development ( by extending the time , raising the temperature or increasing the concentration of developer ) will make the image more lively . In this case , the exposure must have been reduced . For this type of contrast control , adjustments in the order of a half or one f - stop are normally made .
tonal range is compressed and the contrast reduced . This means , for example , that a scene with a limited range of tones , such as on a dull day , can be given more life by push - processing the film . If you are using this technique only to control the contrast , remember to adjust the exposure setting accordingly . Should you plan to reduce contrast by under - developing one stop , for instance , the lens aperture will have to be opened up or the shutter speed slowed down by the equivalent amount . Alternatively , you could alter the film speed rating : for one - stop underdevelopment of Tri - X or HP5 , rate them at ISO200 instead of ISO400 .
The actual procedure varies according to the film / developer combination , and there is even some choice . There are three things that affect the degree of development : the development time ; the temperature ; and the strength of the developer solution . In theory , changing any of these will do the job , but the limits are set by the need for an evenly processed image . Under - development in particular is limited by this , and for this reason it may be better to use a special low - contrast developer ; development times should be at least more than 5 minutes . Overall , the most commonly used technique is altering the time ( this is the only practical choice available to a professional lab , which is processing quantities of film at time most of it normal ) .
SPEED vs CONTRAST
Because altered processing changes both the strength and contrast of the image , it is important to be clear about the effect that you want . Push - proces- sing can be used as a technique for photographing in low light or for higher contrast , or for both . The film speed is adjustable , but the increase in contrast is inevitable , as is an increase in grain . In particular , the shadow areas ( those which receive least exposure and so are palest in the negative ) tend to lose detail , and block up into solid areas of black when the negative is printed . Graininess , as we saw earlier , becomes most obvious in mid - toned areas .
For maximum film speed , select a fast film to begin with , as push - processing a slow or medium film is always less effective than using a film that has been designed for its great sensitivity to light . On the other hand , if you want only to increase the contrast , it is more effective if you choose a slow film - this is already slightly more contrasty than faster emulsions .
Pull - processing is less commonly used , simply because of the circumstances in which most photographs are taken . There is insufficient light for photography more often than there is too much , and the requirement for high contrast in a scene is more usual than lowering it .
Although all of the above assumes that you have planned to change the development from the start , these are also useful emergency procedures in cases where you have made an exposure mistake . The most common is forget- ting to change the meter setting or film speed dial when changing film types . If this happens , simply continue shooting at the ' wrong ' setting ( provided that it is within a correctable range , between about 2 stops under and 3 stops over ) , and make the adjustments to the development .
Under - development gives low contrast ( above ) , over- development gives high ( above right ) . The second shot had been under - exposed to allow for over - development .
ABOVE One by product of the increase in contrast that results from push processing is a loss of detail in shadow areas , which tend to block into solid black Graininess , meanwhile , becomes most obvious in mid toned areas .
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