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Length of exposure and contrast change

redbandit

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when dealing with the ilford and kodak filters, the rule is above a certain contrast number, double the exposure time.

That is never talked about with a COLOR head being used with black and white paper. SO im just curious if there IS a rule of thumb for changing the length of exposure when you change the filtration level with a color head.
 

If you look at the dual or single filtration charts issued by Ilford you will see that for the single Y or M filtration values the Y only values change for the lower contrast grades and are then replaced by the M only values and each set of values, be it Y or M, is given a specific contrast

The same is true of the dual filtration charts but here both values are given for the contrast grades in an attempt to give you constant exposure values across the whole grade range

However in the case of the dual filtration values constant exposure is only maintained over the middle range, say grade 2 to 3 for the rest this is not possible. Look at the top and bottom end of the contrast grade range and you will see that at 5 and 1 one of the dual filtration values disappear to get the grade required so it is impossible to maintain constant exposure

This is one of the drawbacks of using Y and M on a colour head that is largely eliminated by Ilford filters. I made this point in response to a post by Sirius in one of the recent threads that I think you started

It is worth reading the Ilford charts and reading some good books on darkroom work


pentaxuser
 
Color filter values (e.g. 5Y vs 40Y) are representative of DENSITY in the filter (as well as strength of the filter). Variable contrast filter sets have added density in the lower constrast ranges to that a switch between the Grade 2 and Grade 3 filter have near-identical density (while varying the contrast), so that exposure times do not change.

'in the old days' the variable contrast change from 2 to 3 was accompanied by a change in time of exposure, because the added neutral density was not deliberately put into Grade 2 to equalize its exposure time to Grade 3 filter. A Kodak darkroom guide from the mid-1960s shows a change of Polycontrast filter would take 10 second exposure time with Grade 2 increased to 14.5 sec. with Grade 3 filter.
 
Last edited:
Forget the rules. Make a test strip.
 
Sirius Glass said:
Forget the rules. Make a test strip.
Click to expand...

I agree. I use Ilford filters and the instructions say the exposure time for filters 00–3½ is the same, and the exposure time for filters 4–5 doubles. I am sure that is technically correct in terms of the amount of light passing through the filters, but when the contrast changes, the look of the print changes, and you may want more or less exposure to achieve the look you want.
 
OK, my old brain is malfunctiong..it is not controlling the typing fingers properly, nor the proofreading brain cells.
 
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