The contrast of a copy, print or any duplicate stage is the product of the contrasts of all the preceding film materials.
For example:
|
Black and White negative film |
X Black and White Print film |
= Print Contrast |
|
Contrast 0.6 |
X Contrast 2.5 |
= Contrast 1.5 |
The optimum contrast for a projection print seems to be subjectively acceptable to most audiences at 1.5, although some television systems prefer a lower contrast even though they achieve a similar final contrast of 1.5 on the video screen.
This principle applies to colour as well as black and white, and the following are the Eastman negative-positive film contrasts:
|
Eastman Colour Negative film |
X Eastman Colour Print film |
= Print Contrast |
|
Contrast 0.6 |
X Contrast 2.5 |
= Contrast 1.5 |
All duplicating routes must be designed [or manipulated] so that the final print contrast is also the subjectively preferred 1.5. If the starting point is the same negative film stock and the print stock the same print stock then the intermediate stages must combined have a contrast of 1.0 to continue to achieve a final print contrast of 1.5.
|
Colour negative film |
X Interpositive film |
X Duplicate film |
X Print film |
= Print Contrast |
|
Contrast 0.6 |
Contrast 1.0 |
Contrast 1.0 |
Contrast 2.5 |
Contrast 1.5 |
In this instance the interpositive film and the duplicate negative film are the same film stock Eastman Colour Intermediate processed in exactly the same way to a contrast of 1.0.
The preparation of a Black and white duplicate negative uses different film stocks for interpositive and duplicate negative developed to different contrasts, but still producing a combined contrast of 1.0
|
B/W negative film |
X Interpositive film |
X Duplicate film |
X Print film |
= Print Contrast |
|
Contrast 0.6 |
Contrast 0.67 |
Contrast 1.5 |
Contrast 2.5 |
Contrast 1.5 |
The Interpositive film could a blue sensitive material for use from black and white negatives or a panchromatic material for use from a colour film. This panchromatic film is also used for preparing separation negatives and positives [see chapter on colour].
The Black and white duplicating film is always panchromatic and is also used to produce internegatives from colour or black and white prints or reversal originals.
Other duplicating routes, however complex or non-standard will all follow these broad principles, and as a further example this can be seen in the use of Eastman Colour Internegative, originally designed for making a negative from an Ektachrome [reversal] camera film that could then be printed onto conventional Eastman Print film to make a print.
|
Ektachrome Commercial |
X Eastman Internegative |
X Eastman Colour Print |
Print Contrast |
|
Contrast 1.0 |
Contrast 0.6 |
Contrast 2.5 |
Contrast 1.5 |
Ektachrome Commercial had a contrast of 1.0 and was originally designed to print onto a special Kodachrome print film. Today we use Eastman Colour Internegative for making internegatives from a wide range of positives and not surprisingly may need to pre-flash to reduce the contrast of internegative to 0.4 to achieve a final optimum contrast of 1.5 if the original was a conventional print of contrast 1.5 also.
|
Projection Print |
X Eastman Internegative [flashed] |
X Eastman Colour Print |
Print Contrast |
|
Contrast 1.5 |
Contrast 0.4 |
Contrast 2.5 |
Contrast 1.5 |