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الأخطاء والطوارئ - ٢ - المعالجة والطباعة .. كيفية التقاط وتطوير الصور بالأبيض والأسود
FAULTS & EMERGENCIES
EMERGENCY TECHNIQUES
If the film has been over- or under - exposed , choice of paper grade and a dif- ferent exposure in the enlarger will help to an extent , but the negative can also be intensified or reduced in special chemicals . If the negative has been scratched , it may still be possible to make a good print by temporarily coating the emulsion with a thin layer of glycerin . This fills in the scratches and has a refractive index similar to that of the gelatin in the emulsion . If this does not work you will have to retouch the print ; negative retouching is only practical on a large sheet of film .
VIEWING THE NEGATIVE
In order to be able to make a proper assessment of a negative , you must be in a position to study it closely and with efficient back - lighting . The ideal equip- ment is a light box and a loupe ; proprietary light boxes use fluorescent strip- lights backed with white reflecting metal or plastic , covered with a sheet of translucent plastic . They are relatively expensive , but it is fairly straightforward to build your own . The important criterion is that the illumination is even , yet bright .
Not even a home - made light box is entirely necessary . A plain white sheet of paper illuminated by an ordinary desk lamp aimed downwards is effective and simple ; if you then support a plain sheet of glass over this ( on two piles of books , for instance ) , the negative strip can be laid flat for close examination with a loupe .
ASSESSING THE NEGATIVE
Faults apart , an assessment of the density and contrast of the negative will help in planning the print , which we deal with on the following pages . Experience in looking at many different negatives , and then printing them , will show what standard density and normal contrast are . For now , one simple guide to density is to press the negative flat down on a sheet of printed white paper , such as the page of a book . If the exposure and development have been normal , the let- tering should just be visible through the darkest areas in the negative .
Fogging in camera : opaque areas may be visible at the edges of the film , though the middle should be clear .
Scratching : parallel scratches indicate grit either on the film cassette mouth or in the squeegee used to dry the film .
Fogging : opaque areas that should be clean and clear , almost certainly due to light reaching the film while loading into the tank . All - over density throughout the film could also be fogging of a different sort . This could be the remains of silver halide still in the emulsion which has not been " cleared " by fixing . A re - fix can cure the problem . Undeveloped strip : down one side of film , caused by insufficient developer in the tank . All the film must be immersed under the developer . If one film is developed in a two - spiral tank , it is possible for the single spiral to move upward during agitation . Use the securing device supplied with the tank .
RIGHT A bad case of light leaking onto the film , either while it is in the camera or in the cassette , is difficult to correct if all detail is lost .
ABOVE If a negative has suffered a light leak , such as here , choosing a suitable paper grade and altering the print exposure may help matters .
RIGHT Much the same applies when the negative has been over - exposed ; it is possible to increase the contrast in this scene by using either a harder grade of paper or a stronger concentration of paper developer .
FAULTS & EMERGENCIES
EMERGENCY TECHNIQUES
If the film has been over- or under - exposed , choice of paper grade and a dif- ferent exposure in the enlarger will help to an extent , but the negative can also be intensified or reduced in special chemicals . If the negative has been scratched , it may still be possible to make a good print by temporarily coating the emulsion with a thin layer of glycerin . This fills in the scratches and has a refractive index similar to that of the gelatin in the emulsion . If this does not work you will have to retouch the print ; negative retouching is only practical on a large sheet of film .
VIEWING THE NEGATIVE
In order to be able to make a proper assessment of a negative , you must be in a position to study it closely and with efficient back - lighting . The ideal equip- ment is a light box and a loupe ; proprietary light boxes use fluorescent strip- lights backed with white reflecting metal or plastic , covered with a sheet of translucent plastic . They are relatively expensive , but it is fairly straightforward to build your own . The important criterion is that the illumination is even , yet bright .
Not even a home - made light box is entirely necessary . A plain white sheet of paper illuminated by an ordinary desk lamp aimed downwards is effective and simple ; if you then support a plain sheet of glass over this ( on two piles of books , for instance ) , the negative strip can be laid flat for close examination with a loupe .
ASSESSING THE NEGATIVE
Faults apart , an assessment of the density and contrast of the negative will help in planning the print , which we deal with on the following pages . Experience in looking at many different negatives , and then printing them , will show what standard density and normal contrast are . For now , one simple guide to density is to press the negative flat down on a sheet of printed white paper , such as the page of a book . If the exposure and development have been normal , the let- tering should just be visible through the darkest areas in the negative .
Fogging in camera : opaque areas may be visible at the edges of the film , though the middle should be clear .
Scratching : parallel scratches indicate grit either on the film cassette mouth or in the squeegee used to dry the film .
Fogging : opaque areas that should be clean and clear , almost certainly due to light reaching the film while loading into the tank . All - over density throughout the film could also be fogging of a different sort . This could be the remains of silver halide still in the emulsion which has not been " cleared " by fixing . A re - fix can cure the problem . Undeveloped strip : down one side of film , caused by insufficient developer in the tank . All the film must be immersed under the developer . If one film is developed in a two - spiral tank , it is possible for the single spiral to move upward during agitation . Use the securing device supplied with the tank .
RIGHT A bad case of light leaking onto the film , either while it is in the camera or in the cassette , is difficult to correct if all detail is lost .
ABOVE If a negative has suffered a light leak , such as here , choosing a suitable paper grade and altering the print exposure may help matters .
RIGHT Much the same applies when the negative has been over - exposed ; it is possible to increase the contrast in this scene by using either a harder grade of paper or a stronger concentration of paper developer .
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