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Longer development
time produces negatives with greater contrast. By
increasing your development time by 10-25% you can get
a negative with more contrast and more pronounced grain.
Pushing film can also be used to compensate for over-rating
a film’s ASA. For example, you can use a 400
ASA film and rate it to 800. The camera exposes the
film as though it is faster than it is, thus underexposing
it, so to get a printable negative, you will have to develop
it longer.
The amount of over development varies between films and
developers. Most people use a 25-50% rule per stop.
Example chart for 400 speed films (Horenstein
pg. 154):
Push to 800 means underexposed one stop, so overdevelop
by 35-50%
Push to 1600 means underexposed two stops, so overdevelop
by 75-100%
From digitaltruth.com:
PUSH PROCESSING (B/W)
These are general guidelines when no published development
times are available.
To use this chart multiply the published time at recommended
ASA by the factor in parenthesis (ie. If Tri-X rated at
400ASA is normally developed for 6 mins in a standard soup,
then when Tri-X is pushed three stops to 3200ASA development
would be: 6 x 4.5 = 27 mins).
Please use these recommendations as starting points only.
In many cases these times will prove excessive, but when
all else fails they can be a good guideline. Please note
separate data for Tmax films.
Standard
Developer
1 stop push = (x1.5)
2 stop push = (x2.25)
3 stop push = (x4.5)
Compensating Developer
1 stop push = (x1.4)
2 stop push = (x1.85)
3 stop push = (x2.5)
TMax Films
1 stop push = no change
2 stop push = (x1.33)
3 stop push = (x1.66) |
*Compensating developers include
Microphen, TMax, and any other developers which are specifically
formulated for push processing. |
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