The "old" (1968) Kodak Polycontrast enlarger filter exposure adjustment calculator comes with each filter set. Each filter in the set requires an adjustment to exposure times. The circular slide rule shows exposure adjustment in seconds. I wanted to see the f/stop change going between any two filters. I created a simple table in Excel that shows the f/stop adjustment going from any filter (or no filter) to any other filter. It is easy to dial the adjustment into my enlarger f/stop timer when changing filters.
To create the table, I set a no-filter base time on the calculator and read the time adjustments on the dial for each filter. The difference between the base 2 log of each number is the needed adjustment in stops.
A trick for calculating base 2 logarithms in a calculator lacking the function is to use either the base 10 or natural log function and divide the result by the base 10 or natural log of 2. Excel can easily calculate logarithm of any base directly.
Best,
Don
To create the table, I set a no-filter base time on the calculator and read the time adjustments on the dial for each filter. The difference between the base 2 log of each number is the needed adjustment in stops.
A trick for calculating base 2 logarithms in a calculator lacking the function is to use either the base 10 or natural log function and divide the result by the base 10 or natural log of 2. Excel can easily calculate logarithm of any base directly.
Best,
Don
Last edited:
