What is reciprocity failure?

At very long shutter speeds (typically above 1 second), film becomes less sensitive to light. The reciprocal relationship between aperture and shutter speed breaks down, requiring longer exposures than the meter indicates. This is called reciprocity failure or the Schwarzschild effect.

Does digital have reciprocity failure?

No. Digital sensors do not suffer from reciprocity failure. This calculator is specifically for film photography. Digital sensors have their own long-exposure issues (sensor heating, noise) but these are different from reciprocity failure.

Which films have the best reciprocity characteristics?

Fuji Acros 100 II is widely regarded as having the best reciprocity characteristics of any currently available film, requiring almost no correction up to 2 minutes. Kodak T-Max films also perform well due to their tabular grain technology.

Do I need to adjust development for reciprocity?

For B&W film, reduce development by 10-15% for exposures corrected by more than 2 stops to prevent highlights from blocking up. For colour negative film, long exposures can cause colour shifts that may need correction in printing or scanning.

PhotoCalcs

Reciprocity Failure Calculator

Calculate corrected exposure time for film reciprocity failure at long exposures.

Metered Exposure Time

The exposure time your light meter indicates

Time Unit

Unit for the metered time value

Film Stock

Select your film to apply the correct reciprocity factor

How We Calculate This

Corrected time is calculated using the Schwarzschild formula: T_corrected = T_metered ^ p, where p is the reciprocity exponent specific to each film stock.

An exponent of 1.0 means no reciprocity failure (like Fuji Acros at short times). Higher exponents mean more correction is needed. Most films have exponents between 1.1 and 1.35.

Frequently Asked Questions

Related Calculators

Exposure Triangle Calculator

Balance aperture, shutter speed and ISO to achieve correct exposure. Adjust one setting and see how the others compensate. Free online calculator.

EV Calculator

Calculate Exposure Value from your camera settings or convert between EV, lux and foot-candles. Ideal for matching light meter readings. Free calculator.

Reciprocity Calculator

Compensate for reciprocity failure when shooting long exposures on film. Enter metered time and film stock for corrected exposure. Free calculator.

Sunny 16 Calculator

Estimate correct exposure settings using the Sunny 16 rule for outdoor photography. Select lighting conditions for instant aperture and shutter recommendations.

Flash Exposure Calculator

Calculate flash power from guide number, subject distance and aperture. Work out the correct flash-to-subject settings for any strobe. Free calculator.

Last updated: March 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.