تويت
تغييرات الترشيح وتتبع أخطاء الطباعة .. معالجة الألوان والطباعة .. المرشد خطوة بخطوة للتصوير الفوتوغرافي
Filtration changes and tracing printing faults
Judging the color printing exposure is really no more difficult than in black and white printing ( see pp . 80-1 ) . But recognizing color deficiencies and knowing how to use the color filters to make the right correc- tions require more practice and skill .
For consistent and accurate results stan- dardize the lighting conditions you use for viewing your prints . Try to assess your tests in the same lighting by which the final print will be seen . This may involve installing special " color - matching " fluorescent tube or a " daylight " lamp in your darkroom .
You can begin to judge the correct filtra- tion for the image by viewing the most accurate - looking section on the second test strip through different printing filters , until you find one which makes the midtones in one band.look correct . Then remove a filter half that strength but of the same color from the filter pack to make the next print . ( Al- ternatively , add a half - strength filter in the complementary color . )
The ring - around on page 167 illustrates the amount of color shift you can expect each filter change to produce . Filters of 10 or less give slight changes ; 15 or 20 have a moderate effect . Filters over 20 give a major change you will need to make a further test strip to adjust the print color if you have to use a filter of this strength .
Check the new filter pack for neutral density and if necessary alter the filtration so that only two of the three basic filter colors are in use . Lastly , look at your filter calculator or the table below to see if the altered filtration requires a change in the exposure time for the print .
Paper batch changes
You must alter the filtration and exposure slightly if you change paper batches .
To calculate the new filtration , begin by subtracting from the values of your filter pack the recommended filtration values for the paper batch you have finished using . For example , if your present filtration is 50Y 30M , and the recommended filtration for the paper was + 15Y OOM , subtracting them would give you 35Y 30M . To find the new filtration , add this result to the values printed on the new batch label . In this example , if the new batch values are + 20Y + 20M , the new filtration would be 55Y 50M . Finally , to obtain the new exposure time , divide the exposure factor on the new label by the one on the old label , and multiply this by the old exposure time .
Exposure adjustments for filter changes
Each time you change the expo- sure filtration you must recalculate the exposure time .
To find your new exposure , first divide your original time by the factor for each filter you have re- moved . Then multiply it by the factor for each one you have added . For example , removing a Kodak 50M and using a 20M filter instead means altering a 9 second exposure to 6 seconds ( to the nearest whole second ) .
Printing faults
Appearance ---- Cause
Yellow or brown streaks :
White light fog from a badly blacked out darkroom .
Cyan or blue fog :
Orange safelight left on during printing .
Stains :
Chemical contamination . Devel- oper in the bleach gives a cyan stain , or cyan and magenta streaks . Stabilizer contaminated with bleach or fixer stains the print yellow .
Poor yellows :
Weak bleach - fixer , or insuf- ficient time in this solution .
Shadows and highlights tinted different colors :
Reciprocity failure from long exposures , typically of 40 seconds or more .
Bleached color :
Bleached filters check for this by comparing old and new filters against white paper .
Uneven color :
This is caused by lack of agitation , using too little of the chemical solutions , or loading the paper into drum emulsion side outward .
Inconsistent color :
If your enlarger lamp is new it needs " burning in " - running for an hour or so to reach a steady color temperature .
Reminders : Color processing and printing
The way negative and slide films work :
Color negative film processing turns the latent images in the three emulsion layers into com- plementary colored negative images . Slide film processing forms black and white negatives . and then turns the remaining emulsion into complementary colored positive images .
Always follow the temperatures times , and agitation recommended with the processing kit :
In color processing , consistency and care are essential if you want to get good results . You must maintain the high temperatures : agitate the solutions evenly ; follow the recommended times ; and avoid contaminating the chemicals .
The advantages of additive and subtractive printing :
You can control the color on a print by additive or subtractive use of filters . Additive printing is cheaper , needing only three filters , but subtractive printing is quicker and more practical .
Color printing requires two tests :
In color printing always test first for exposure , then for color . The main skill in color printing is judging the filtration needed for accurate color results . To remove a cast add filters which match that color . Record the exposure and filtration on the back of every print . Avoid creating neut- ral density in your filtration .
Filtration changes and tracing printing faults
Judging the color printing exposure is really no more difficult than in black and white printing ( see pp . 80-1 ) . But recognizing color deficiencies and knowing how to use the color filters to make the right correc- tions require more practice and skill .
For consistent and accurate results stan- dardize the lighting conditions you use for viewing your prints . Try to assess your tests in the same lighting by which the final print will be seen . This may involve installing special " color - matching " fluorescent tube or a " daylight " lamp in your darkroom .
You can begin to judge the correct filtra- tion for the image by viewing the most accurate - looking section on the second test strip through different printing filters , until you find one which makes the midtones in one band.look correct . Then remove a filter half that strength but of the same color from the filter pack to make the next print . ( Al- ternatively , add a half - strength filter in the complementary color . )
The ring - around on page 167 illustrates the amount of color shift you can expect each filter change to produce . Filters of 10 or less give slight changes ; 15 or 20 have a moderate effect . Filters over 20 give a major change you will need to make a further test strip to adjust the print color if you have to use a filter of this strength .
Check the new filter pack for neutral density and if necessary alter the filtration so that only two of the three basic filter colors are in use . Lastly , look at your filter calculator or the table below to see if the altered filtration requires a change in the exposure time for the print .
Paper batch changes
You must alter the filtration and exposure slightly if you change paper batches .
To calculate the new filtration , begin by subtracting from the values of your filter pack the recommended filtration values for the paper batch you have finished using . For example , if your present filtration is 50Y 30M , and the recommended filtration for the paper was + 15Y OOM , subtracting them would give you 35Y 30M . To find the new filtration , add this result to the values printed on the new batch label . In this example , if the new batch values are + 20Y + 20M , the new filtration would be 55Y 50M . Finally , to obtain the new exposure time , divide the exposure factor on the new label by the one on the old label , and multiply this by the old exposure time .
Exposure adjustments for filter changes
Each time you change the expo- sure filtration you must recalculate the exposure time .
To find your new exposure , first divide your original time by the factor for each filter you have re- moved . Then multiply it by the factor for each one you have added . For example , removing a Kodak 50M and using a 20M filter instead means altering a 9 second exposure to 6 seconds ( to the nearest whole second ) .
Printing faults
Appearance ---- Cause
Yellow or brown streaks :
White light fog from a badly blacked out darkroom .
Cyan or blue fog :
Orange safelight left on during printing .
Stains :
Chemical contamination . Devel- oper in the bleach gives a cyan stain , or cyan and magenta streaks . Stabilizer contaminated with bleach or fixer stains the print yellow .
Poor yellows :
Weak bleach - fixer , or insuf- ficient time in this solution .
Shadows and highlights tinted different colors :
Reciprocity failure from long exposures , typically of 40 seconds or more .
Bleached color :
Bleached filters check for this by comparing old and new filters against white paper .
Uneven color :
This is caused by lack of agitation , using too little of the chemical solutions , or loading the paper into drum emulsion side outward .
Inconsistent color :
If your enlarger lamp is new it needs " burning in " - running for an hour or so to reach a steady color temperature .
Reminders : Color processing and printing
The way negative and slide films work :
Color negative film processing turns the latent images in the three emulsion layers into com- plementary colored negative images . Slide film processing forms black and white negatives . and then turns the remaining emulsion into complementary colored positive images .
Always follow the temperatures times , and agitation recommended with the processing kit :
In color processing , consistency and care are essential if you want to get good results . You must maintain the high temperatures : agitate the solutions evenly ; follow the recommended times ; and avoid contaminating the chemicals .
The advantages of additive and subtractive printing :
You can control the color on a print by additive or subtractive use of filters . Additive printing is cheaper , needing only three filters , but subtractive printing is quicker and more practical .
Color printing requires two tests :
In color printing always test first for exposure , then for color . The main skill in color printing is judging the filtration needed for accurate color results . To remove a cast add filters which match that color . Record the exposure and filtration on the back of every print . Avoid creating neut- ral density in your filtration .
تعليق