Reciprocity Failure Correction
Correct long film exposures for reciprocity failure and the added exposure time.
About Reciprocity Failure Correction
Beyond a few seconds, film reacts non-linearly, so the corrected time is the metered time raised to the reciprocity factor. Without correction, long exposures come out underexposed, frustratingly so for astro and night work on film.
Formula
Reciprocity Failure Correction
Corrected = exposure^reciprocity factor
- factor
- Film-dependent exponent above the reciprocal realm
Worked example
With the default values below, Reciprocity Failure Correction returns Corrected Exposure of 464.8. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Metered exposureminimum 0.1
- 60
- Reciprocity factoraccepts 1–3
- 1.5
Results
- Corrected Exposure
- 464.8 s
- Added Stops
- 2.95
- Extra Time Needed
- 404.8 s
Step by step
- 1Values used
- 2Reciprocity Failure Correction
- 3Corrected Exposure= 464.8 s
- 4Added Stops= 2.95
- 5Extra Time Needed= 404.8 s
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Reciprocity Failure Correction calculated?
Corrected = exposure^reciprocity factor Beyond a few seconds, film reacts non-linearly, so the corrected time is the metered time raised to the reciprocity factor.
Why does Reciprocity Failure Correction matter?
Without correction, long exposures come out underexposed, frustratingly so for astro and night work on film.
What values do I need to enter?
This calculator takes 2 inputs: Metered exposure, Reciprocity factor. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.