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Film calculator
Reciprocity Failure
Film breaks the reciprocity law at long exposures. Select your film stock, drag the slider — get your corrected exposure time instantly.
14.5s
corrected exposure
Kodak Portra 400
Film stock
Kodak colour
Ilford B&W
Fuji
Cinestill
Metered exposure 10s
1s30s2 min5 min
Compensation chart — metered vs corrected
10s
Metered
+4.5s
Extra time
+0.54
Stops added
14.5s
Corrected exposure
Set this on your camera
10s
Metered time
What your meter says
+4.5s
Extra time
Due to reciprocity failure
+0.54
Stops compensation
Actual exposure increase
Kodak Portra 400
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Film note
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Corrected time = tᵃ where p is the Schwarzschild exponent per film stock. Based on manufacturer data and community testing. Always bracket on critical shots.