تويت
التصوير الفوتوغرافي الحديث
تطوير السلبية ..
النقاط الدقيقة في معالجة الفيلم ..
المطور ..
FINE POINTS IN PROCESSING FILM
You have learned how to develop film following an entirely satisfactory method for average results . But the photographer who isn't satisfied with just average results can do much understands what happens at each step . He can choose the right film for the type of pictures he wants to take , and he can develop it the right way to bring out the results he wants . Not only will he get better pictures , but he will enjoy photography more .
THE DEVELOPER
When a film is exposed in a camera and light strikes the silver compounds ( mainly silver bromide ) in the emulsion , it breaks them down , releasing silver as a pure metal . This reaction is extremely slow , and it takes tremendous quantities of light to produce an appreciable deposit of silver . However , if a film which has been exposed only briefly to light is immersed in certain chemical solutions called . developers , these solutions will continue the action started by the light during exposure . The developer rapidly breaks down additional silver - bromide crystals to form a relatively heavy deposit of silver - enough to produce an image .
A developer is not a simple solution , but a carefully compounded prescription of various chemicals , each of which performs a specific and important function . The developer must be able to break down silver bromide and release free silver . However , it must be so delicately balanced that it needs help before it can start to work . This help is provided by the many microscopic particles of free silver produced when light strikes the silver bromide in the emulsion . With this silver as a base , additional silver can accumulate around it when the developer starts working . The amount of silver released by the developer is in proportion to the exposure .
With but few exceptions , all developing solutions contain the following :
1. Developing agent
2. Accelerator
3. Preservative
4. Restrainer
5. Water
Since the proportion of each of these ingredients may be varied through wide limits to achieve specific results , the following description of each will enable you to gain a much better understanding of the results you may expect when changing from one formula to another you mix your own developers .
THE DEVELOPING AGENT . The developing agent is the heart of the developing solution . It is the chemical that continues the breaking down of the silver bromide crystals started by exposure to light . Developing agents differ in many respects , such as their vigor ( speed with which they work on the film ) , their ability to distinguish between exposed and unexposed silver bromide ( this determines contrast ) , the size and arrangement of the silver particles they produce ( color and graininess of the image ) , and the degree to which they react with the oxygen of the air ( keeping qualities ) . As a result , each has its special application . It is possible to select any one , or a combination of developing agents , to produce the best picture under any set of circumstances .
THE ACCELERATOR . With very few exceptions , developers work well , if at all , only when the solution is alkaline ( the chemical opposite of acid ) . The speed of development increases rapidly as alkalinity goes up . For this reason , the alkali in a developer is frequently called the accelerator .
We have a wide choice of alkalis in compounding developer formulas . If you require an extremely quick - acting and contrasty developer , you can use a very strong alkali such as sodium hydroxide or a strong solution of sodium carbonate . For average results , you would use alkalis of medium strength such as sodium carbonate or sodium metaborate ( Kodalk ) . If you require a mild alkali , for a slow - acting , fine - grain developer , you can use borax . Actually , the alkali can be . left out altogether , and you can rely on the very mild alkaline reaction of the sodium sulfite which is used in almost all developers as a preservative .
THE PRESERVATIVE . Developing agents all have a tendency to react with the oxygen of the air , and over a period of time become exhausted even without use . Sodium sulfite , which greatly retards this reaction is added as a preservative to practically all developer formulas .
One of the properties of sodium sulfite , aside from its action as a preservative , is that it dissolves silver bromide at an appreciable rate . This dissolved silver bromide is in turn developed by the developer . The silver thus formed may be deposited either upon the silver grains previously formed , or indiscriminately throughout the emulsion . If it builds up on the silver grains previously formed , it simply increases density . However , if it spreads throughout the emulsion , it creates fogged negatives . This tendency of a developer to produce a silver deposit where none is wanted , can be prevented by the addition of a restrainer .
THE RESTRAINER . Restrainers function in two ways . They either retard solution of the silver bromide , or they combine with the dissolved silver bromide to form a new compound which is not easily developed . Potassium bromide , by far the most commonly used restrainer , works on the first principle - it slows up solution of the silver bromide . It also has a restraining action on the developing process itself .
WATER . Water is in many ways the most important ingredient of a developing solution . Yet it is the one most likely to be overlooked . Almost any kind of water is good enough for fixing solutions or stop baths , but the water used for film developers should be reasonably free of dissolved and suspended matter . Fortunately , most water which is fit to drink is pure enough for photographic use . Water which contains a high percentage of dissolved calcium salts will tend to form sludges with most photographic solutions . The addition of small amounts of an agent which holds the calcium in solution ( such as Kodak's Anti - Cal ) will help keep such solutions clear .
Ordinarily , it is not necessary to use distilled water in mixing developers . The slight amount of impurities contained in most tap water will do no harm , even though a slight sludging may result . There are times , however , when distilled water may be used to advantage . If the tap water has an appreciable alkaline or acid reaction , or contains metallic impurities , it is not suitable for fine - grain developers . Also , if maximum keeping qualities of developer are important , it is wise to use distilled water .
When distilled water is not available , clean rain water makes a good substitute except in heavily industrialized communities where the air contains harmful impurities which may be picked up by the rain . In that case , the water collected from the defrosting of a refrigerator or from a dehumidifier may be used instead . Any lint or sediment can be removed by filtering , and slight food odors driven off by boiling . Do not use any special bottled drinking water , regardless of its clarity . Such water may contain a good deal of dissolved matter which may be quite unsuited for photographic use .
EFFECT OF TEMPERATURE ON DEVELOPMENT . Because temperature has such an important effect on the speed of development , it is necessary to establish a standard temperature and then give the correct time of development for this temperature . Most manufacturers use 68 ° F . ( 20 ° C ) as a development standard , although some manufacturers prefer to establish 70 ° F . as their standard temperature .
Within fairly narrow limits , it is possible to adjust development time to higher or lower temperatures . For example , development time for a medium - speed film with a certain developer is given as 7 minutes at 68 ° F . At 65 ° F. correct development time is 8 minutes ; at 70 ° F. , it is 6 minutes .
It is not possible to give a universal temperature compensating factor . Not all developers and films respond to temperature changes to the same degree . For that reason , most manufacturers supply time - temperature charts or tables for their products . A typical time - temperature curve is shown in Figure 27 .
TIME OF DEVELOPMENT ( MINUTES )
Fig . 27 Time - Temperature Chart : Such a chart . shows the correct development time for a range of temperatures .
There are limits to the temperature range that can be used for development . Below 60 ° F. ( sometimes 65 ° F . ) , the delicate balance of the developer is disturbed so much that it cannot be used successfully . Above 75 ° F . the gelatin emulsion may soften too much . Therefore , it is best to work between the limits of 65 ° F . and 75 ° F . when developing film . Prints can be developed safely at much higher temperatures because the emulsion is much harder and tougher .
COMPENSATING FOR DEVELOPER EXHAUSTION . If you develop only an occasional film at intervals of several weeks , it is best to select a developer which you use once and throw away . This type of developer usually comes in a concentrated form . It keeps for months if stored in a cool place in a tightly stoppered bottle . You dilute enough of the concentrated stock to fill your tank , use it once , and discard it . You are thus assured of uniform results every time . Many photographers prefer this method even when they do quite a lot of work .
However , a tankful of developer can be used to develop considerably more than one roll of film , and it is wasteful to throw away a developer when it still has a lot of useful life . Two methods are generally used to get full value from a developer . You may use the same batch of developer several times , but increase the development time after each roll . This compensates for developer exhaustion . This method works quite well with certain developers , but you must be sure to follow the manufacturer's instructions , and don't develop more film than is recommended . Some developers , when pushed too far , stop working almost completely without advance warning .
A second method called the replenisher method is more practical where the developer is to be used to process a relatively large amount of film over a period of time . In this method , you add a specific quantity of a special replenishing solution for each roll developed . Here , too , you must follow instructions carefully .
Using replenisher solutions has its limitations . The proportion of each ingredient in a replenisher formula has been calculated to make up for average exhaustion with average frequency of use . A developer used daily does not become exhausted in the same manner as a developer used weekly or monthly - in the latter case the reaction between the developer and air becomes a more important factor than exhaustion through use . To compensate correctly for both conditions is not practical . For that reason it is best to keep close watch on your negatives and vary the amount of replenisher slightly to increase or decrease negative contrast as needed .
Do not attempt to replenish a developer indefinitely . After some time , it will accumulate a silver sludge as well as particles of dirt and hard gelatin . These may settle on the film to cause spots and streaks . When a developer shows signs of stain or fog , or when its strength differs so much from standard that development time must be changed appreciably to get negatives of acceptable contrast , it is best to throw it away and start with a new solution . This also applies to a developer which has become badly discolored , either through use or age .
As a rough guide to the useful life of a replenished developer , it is customary to discard such a developer when the amount of replenisher which has been added to it is equal to the original volume of developer . For example , if 32 ounces of developer is kept working until an additional 32 ounces of replenisher has been added , it is time to throw it away . By that time the formula has been so changed by the addition of replenisher and by the accumulation of the products of development that it is no longer wise to continue its use .
تطوير السلبية ..
النقاط الدقيقة في معالجة الفيلم ..
المطور ..
FINE POINTS IN PROCESSING FILM
You have learned how to develop film following an entirely satisfactory method for average results . But the photographer who isn't satisfied with just average results can do much understands what happens at each step . He can choose the right film for the type of pictures he wants to take , and he can develop it the right way to bring out the results he wants . Not only will he get better pictures , but he will enjoy photography more .
THE DEVELOPER
When a film is exposed in a camera and light strikes the silver compounds ( mainly silver bromide ) in the emulsion , it breaks them down , releasing silver as a pure metal . This reaction is extremely slow , and it takes tremendous quantities of light to produce an appreciable deposit of silver . However , if a film which has been exposed only briefly to light is immersed in certain chemical solutions called . developers , these solutions will continue the action started by the light during exposure . The developer rapidly breaks down additional silver - bromide crystals to form a relatively heavy deposit of silver - enough to produce an image .
A developer is not a simple solution , but a carefully compounded prescription of various chemicals , each of which performs a specific and important function . The developer must be able to break down silver bromide and release free silver . However , it must be so delicately balanced that it needs help before it can start to work . This help is provided by the many microscopic particles of free silver produced when light strikes the silver bromide in the emulsion . With this silver as a base , additional silver can accumulate around it when the developer starts working . The amount of silver released by the developer is in proportion to the exposure .
With but few exceptions , all developing solutions contain the following :
1. Developing agent
2. Accelerator
3. Preservative
4. Restrainer
5. Water
Since the proportion of each of these ingredients may be varied through wide limits to achieve specific results , the following description of each will enable you to gain a much better understanding of the results you may expect when changing from one formula to another you mix your own developers .
THE DEVELOPING AGENT . The developing agent is the heart of the developing solution . It is the chemical that continues the breaking down of the silver bromide crystals started by exposure to light . Developing agents differ in many respects , such as their vigor ( speed with which they work on the film ) , their ability to distinguish between exposed and unexposed silver bromide ( this determines contrast ) , the size and arrangement of the silver particles they produce ( color and graininess of the image ) , and the degree to which they react with the oxygen of the air ( keeping qualities ) . As a result , each has its special application . It is possible to select any one , or a combination of developing agents , to produce the best picture under any set of circumstances .
THE ACCELERATOR . With very few exceptions , developers work well , if at all , only when the solution is alkaline ( the chemical opposite of acid ) . The speed of development increases rapidly as alkalinity goes up . For this reason , the alkali in a developer is frequently called the accelerator .
We have a wide choice of alkalis in compounding developer formulas . If you require an extremely quick - acting and contrasty developer , you can use a very strong alkali such as sodium hydroxide or a strong solution of sodium carbonate . For average results , you would use alkalis of medium strength such as sodium carbonate or sodium metaborate ( Kodalk ) . If you require a mild alkali , for a slow - acting , fine - grain developer , you can use borax . Actually , the alkali can be . left out altogether , and you can rely on the very mild alkaline reaction of the sodium sulfite which is used in almost all developers as a preservative .
THE PRESERVATIVE . Developing agents all have a tendency to react with the oxygen of the air , and over a period of time become exhausted even without use . Sodium sulfite , which greatly retards this reaction is added as a preservative to practically all developer formulas .
One of the properties of sodium sulfite , aside from its action as a preservative , is that it dissolves silver bromide at an appreciable rate . This dissolved silver bromide is in turn developed by the developer . The silver thus formed may be deposited either upon the silver grains previously formed , or indiscriminately throughout the emulsion . If it builds up on the silver grains previously formed , it simply increases density . However , if it spreads throughout the emulsion , it creates fogged negatives . This tendency of a developer to produce a silver deposit where none is wanted , can be prevented by the addition of a restrainer .
THE RESTRAINER . Restrainers function in two ways . They either retard solution of the silver bromide , or they combine with the dissolved silver bromide to form a new compound which is not easily developed . Potassium bromide , by far the most commonly used restrainer , works on the first principle - it slows up solution of the silver bromide . It also has a restraining action on the developing process itself .
WATER . Water is in many ways the most important ingredient of a developing solution . Yet it is the one most likely to be overlooked . Almost any kind of water is good enough for fixing solutions or stop baths , but the water used for film developers should be reasonably free of dissolved and suspended matter . Fortunately , most water which is fit to drink is pure enough for photographic use . Water which contains a high percentage of dissolved calcium salts will tend to form sludges with most photographic solutions . The addition of small amounts of an agent which holds the calcium in solution ( such as Kodak's Anti - Cal ) will help keep such solutions clear .
Ordinarily , it is not necessary to use distilled water in mixing developers . The slight amount of impurities contained in most tap water will do no harm , even though a slight sludging may result . There are times , however , when distilled water may be used to advantage . If the tap water has an appreciable alkaline or acid reaction , or contains metallic impurities , it is not suitable for fine - grain developers . Also , if maximum keeping qualities of developer are important , it is wise to use distilled water .
When distilled water is not available , clean rain water makes a good substitute except in heavily industrialized communities where the air contains harmful impurities which may be picked up by the rain . In that case , the water collected from the defrosting of a refrigerator or from a dehumidifier may be used instead . Any lint or sediment can be removed by filtering , and slight food odors driven off by boiling . Do not use any special bottled drinking water , regardless of its clarity . Such water may contain a good deal of dissolved matter which may be quite unsuited for photographic use .
EFFECT OF TEMPERATURE ON DEVELOPMENT . Because temperature has such an important effect on the speed of development , it is necessary to establish a standard temperature and then give the correct time of development for this temperature . Most manufacturers use 68 ° F . ( 20 ° C ) as a development standard , although some manufacturers prefer to establish 70 ° F . as their standard temperature .
Within fairly narrow limits , it is possible to adjust development time to higher or lower temperatures . For example , development time for a medium - speed film with a certain developer is given as 7 minutes at 68 ° F . At 65 ° F. correct development time is 8 minutes ; at 70 ° F. , it is 6 minutes .
It is not possible to give a universal temperature compensating factor . Not all developers and films respond to temperature changes to the same degree . For that reason , most manufacturers supply time - temperature charts or tables for their products . A typical time - temperature curve is shown in Figure 27 .
TIME OF DEVELOPMENT ( MINUTES )
Fig . 27 Time - Temperature Chart : Such a chart . shows the correct development time for a range of temperatures .
There are limits to the temperature range that can be used for development . Below 60 ° F. ( sometimes 65 ° F . ) , the delicate balance of the developer is disturbed so much that it cannot be used successfully . Above 75 ° F . the gelatin emulsion may soften too much . Therefore , it is best to work between the limits of 65 ° F . and 75 ° F . when developing film . Prints can be developed safely at much higher temperatures because the emulsion is much harder and tougher .
COMPENSATING FOR DEVELOPER EXHAUSTION . If you develop only an occasional film at intervals of several weeks , it is best to select a developer which you use once and throw away . This type of developer usually comes in a concentrated form . It keeps for months if stored in a cool place in a tightly stoppered bottle . You dilute enough of the concentrated stock to fill your tank , use it once , and discard it . You are thus assured of uniform results every time . Many photographers prefer this method even when they do quite a lot of work .
However , a tankful of developer can be used to develop considerably more than one roll of film , and it is wasteful to throw away a developer when it still has a lot of useful life . Two methods are generally used to get full value from a developer . You may use the same batch of developer several times , but increase the development time after each roll . This compensates for developer exhaustion . This method works quite well with certain developers , but you must be sure to follow the manufacturer's instructions , and don't develop more film than is recommended . Some developers , when pushed too far , stop working almost completely without advance warning .
A second method called the replenisher method is more practical where the developer is to be used to process a relatively large amount of film over a period of time . In this method , you add a specific quantity of a special replenishing solution for each roll developed . Here , too , you must follow instructions carefully .
Using replenisher solutions has its limitations . The proportion of each ingredient in a replenisher formula has been calculated to make up for average exhaustion with average frequency of use . A developer used daily does not become exhausted in the same manner as a developer used weekly or monthly - in the latter case the reaction between the developer and air becomes a more important factor than exhaustion through use . To compensate correctly for both conditions is not practical . For that reason it is best to keep close watch on your negatives and vary the amount of replenisher slightly to increase or decrease negative contrast as needed .
Do not attempt to replenish a developer indefinitely . After some time , it will accumulate a silver sludge as well as particles of dirt and hard gelatin . These may settle on the film to cause spots and streaks . When a developer shows signs of stain or fog , or when its strength differs so much from standard that development time must be changed appreciably to get negatives of acceptable contrast , it is best to throw it away and start with a new solution . This also applies to a developer which has become badly discolored , either through use or age .
As a rough guide to the useful life of a replenished developer , it is customary to discard such a developer when the amount of replenisher which has been added to it is equal to the original volume of developer . For example , if 32 ounces of developer is kept working until an additional 32 ounces of replenisher has been added , it is time to throw it away . By that time the formula has been so changed by the addition of replenisher and by the accumulation of the products of development that it is no longer wise to continue its use .
تعليق