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Film Reciprocity Failure Calculator
Corrected exposure time for long film exposures.
s
How it works
Film loses sensitivity in long exposures. The common Schwarzschild correction is Tc = Tm^p, applied for metered times over one second. The exponent depends on the film: Ilford quotes roughly 1.26 for FP4 Plus and 1.31 for HP5 Plus, but always check the datasheet for your stock. Colour film may also need filtration to cancel colour shifts. Example: A 10 second metered exposure with p = 1.31 becomes 20.4 s, which is 1 stop more.
FAQ
Is this calculator free?
Yes. No signup is needed and nothing you enter is stored.
Is the result exact?
Results are rounded for display. For financial, medical, or legal decisions, confirm with a professional.
Do my numbers leave my device?
No. The calculation runs in your browser.