Reciprocity Failure Calculator
Corrected exposure times for long exposures on 22 film stocks.
Calculate Corrected Exposure
Select your film stock and enter the metered exposure time. The calculator will show the corrected time accounting for reciprocity failure.
Common Exposure Corrections
The table below shows corrected times for common metered exposures with the selected film stock. Times under 1 second do not require correction.
| Metered | Corrected | Added Time |
What Is Reciprocity Failure?
In normal photography, doubling the exposure time doubles the amount of light reaching the film — a linear, reciprocal relationship. But when exposure times exceed roughly one second, this relationship breaks down. The film becomes less efficient at capturing light, requiring progressively more time than your meter indicates. This phenomenon is called reciprocity failure (or reciprocity law failure).
The Correction Formula
The standard correction formula used by TLR Companion and this calculator is:
corrected_time = metered_timeexponent
Each film stock has a unique exponent that determines how severely it is affected by reciprocity failure. A lower exponent means less correction is needed, making the film better suited for long exposures. For example, Kodak T-Max 100 (exponent 1.15) needs far less correction than Kodak Tri-X 400 (exponent 1.33) at the same metered time.
When Does It Matter?
Reciprocity failure is only relevant for exposures longer than approximately one second. This typically occurs in:
- Landscape photography at dawn, dusk, or in deep shade
- Night photography and astrophotography
- Long exposure creative work (waterfalls, light trails, etc.)
- Indoor photography without flash in dim conditions
- Pinhole photography, where all exposures are inherently long
For exposures under one second, no correction is needed — the reciprocity law holds true.
All Film Exponents
Sorted from lowest (least correction needed) to highest (most correction needed).
| Kodak T-Max 100 | 1.15 |
| Kodak Ektar 100 | 1.18 |
| Kodak Ektachrome E100 | 1.20 |
| Fujifilm Provia 100F | 1.22 |
| Fujifilm Velvia 50 | 1.25 |
| Fujifilm Pro 400H | 1.25 |
| Fujifilm Superia 100 | 1.25 |
| Ilford FP4 Plus | 1.26 |
| Fomapan 100 | 1.30 |
| Kodak Portra 400 | 1.30 |
| Kodak Portra 160 | 1.30 |
| CineStill 800T | 1.30 |
| Kodak Gold 200 | 1.30 |
| Kodak ColorPlus 200 | 1.30 |
| Kodak UltraMax 400 | 1.30 |
| Fujifilm Superia 400 | 1.30 |
| Lomography Color 400 | 1.30 |
| Lomography Color 800 | 1.30 |
| Ilford HP5 Plus | 1.31 |
| Ilford Delta 3200 | 1.33 |
| Kodak Tri-X 400 | 1.33 |
| Ilford Pan F Plus | 1.33 |
Reciprocity exponents sourced from manufacturer technical data sheets where available. Community-validated values used for films without published manufacturer data.
Automatic reciprocity correction in your pocket
TLR Companion is a free light meter app that automatically applies reciprocity correction for all 22 film stocks. Just select your film, meter the scene, and the app handles the math. No tables, no mental arithmetic. Learn how it works.