
If the adjustments given are accurate for this film, a bit of curve fitting (I use SciDAVis, which is free and open source) shows that the the following formula should work well.
adjusted time = 0.134353883987194*metered time^1.34968890243641+metered time
(trim to your desired level of pointless 'precision')
I usually make up a small spreadsheet to create a table showing standard meter exposure time readouts and the corresponding corrected exposure times using a formula of this form. I print out and carry the table in my camera bag and use it to determine exposure times corrected for reciprocity. A number of shots made at various corrected exposure times will quickly tell you if the corrections are suitable.
If you prefer to use a Schwarzschild or modified Schwarzschild formula, the approximate Schwarzschild exponent for the adjustments given is 0.90.
Lee
Last edited by Lee L; 06112010 at 11:19 PM. Click to view previous post history.