What is reciprocity failure?

Reciprocity failure (Schwarzschild effect) is the loss of effective film speed at very long exposures. The reciprocity law states that exposure = intensity × time, but at long durations silver-halide crystals become less efficient, so doubling the time no longer doubles the density. You must expose significantly longer than the meter suggests.

Which film stocks have the least reciprocity failure?

Fuji Neopan Acros II and Ilford Delta 100/400 are well-known for low reciprocity failure. Acros II in particular needs almost no correction up to around 120 seconds. Slide films like Velvia 50 have severe reciprocity failure and need large corrections.

Does reciprocity failure affect color balance?

Yes, especially with color negative and slide films. Different color layers respond at slightly different rates, so very long exposures can produce color casts. A CC filter pack is sometimes used to compensate; correction data is in the film datasheet.

Do I need to adjust for reciprocity failure under 1 second?

Most film stocks are accurate within their rated speed from about 1/1000s to 1s. Some high-speed films show minor effects below 1/1000s, but for practical purposes reciprocity failure only matters when your metered time is 1 second or more.

What formula does this calculator use?

For films with manufacturer stop-compensation tables, the calculator converts the stated stop adjustment to a time multiplier and interpolates between published exposure points. Other stocks use the named power-law estimate shown with the result; always check the current film datasheet.

Film Reciprocity Failure Calculator

Enter your metered exposure time and film stock to get the corrected long-exposure time that compensates for reciprocity failure.

Reciprocity Calculator

Film Stock

Metered Exposure Time

Time your light meter shows — before correction.

Quick Presets (metered seconds)

Select a film stock and enter your metered time to see the corrected exposure.

Summary

Film reciprocity failure (also called the Schwarzschild effect) occurs when film sensitivity drops at very long or very short exposures, causing underexposure if you use the metered time directly. Each film stock has its own reciprocity curve. This calculator applies the manufacturer-derived correction formula for the selected stock and returns the adjusted shutter time you actually need to set.

How it works

Select your film stock from the dropdown.
Enter the metered exposure time in seconds (the time your light meter recommends).
The calculator applies the stock-specific reciprocity correction formula.
Read the corrected exposure time and the extra time needed.
Use the corrected time on your camera or cable release timer.

Use cases

Night photography on film where exposures exceed a few seconds.
Astrophotography with film — star trails or landscape under the Milky Way.
Architectural interiors photographed with slow film at small apertures.
Waterfall long exposures on slide film such as Fuji Velvia.
Pinhole photography where exposures routinely exceed 30 seconds.
Any film exposure beyond 1 second where the metered time will underexpose.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu

Metered time	—
Reciprocity correction factor	—
Extra time to add	—
Corrected time	—