Darkroom / ordinary-timer exposure card
f stop test strip calculator
Start with the shortest exposure. Get successive timer settings for a test strip that you cover progressively—not uncover.
Enter these timer settings in order
Each number is one exposure operation—not a cumulative total.
Finished section totals, in covering order
Switch the enlarger off while moving the card. Number sections in the direction you will cover them; the last section stays exposed throughout.
Covering procedure: Darkroom Automation: Progressive Test Prints.
Numbered exposure card
Short timer operation. At least one setting is below one second. Darkroom Automation advises avoiding sub-second exposures unless the enlarger uses an LED light source or a shutter. Check your equipment before using these settings. Manufacturer’s timing notes.
Ideal targets versus timer-rounded totals
| Section | Ideal total | Rounded total | Timer setting |
|---|
How the exposure card is calculated
A whole stop doubles exposure time. The formula below follows from that relationship. Darkroom Automation distinguishes progressive covering from separate individual tests. Read the manufacturer’s stops and test-strip instructions.
Tᵢ = B × 2^(i × d)
Kᵢ = floor(Tᵢ / r + 0.5)
Qᵢ = Kᵢ × r
A₀ = Q₀; Aᵢ = (Kᵢ − Kᵢ₋₁) × r
B = entered base time; d = stop interval; r = timer resolution; i = zero-based section index. T is the ideal total, K the integer tick count, Q the rounded total, and A the timer setting.
Round totals first, then subtract
This calculator rounds cumulative targets to the nearest timer tick, with halfway values rounded upward. That policy is an implementation choice, not a manufacturer’s rule. Integer tick differences make every prefix of the timer sequence reconcile with its rounded section total.
The entered decimal base is retained exactly for rounding comparisons. Half-tick decisions use integer arithmetic, including for fractional-stop targets, so binary floating-point division cannot push a decimal halfway value downward.
Rounded totals approximate equal-stop spacing. If the base rounds to zero, or adjacent sections round to the same total, no card is issued. Increase the base time or stop interval, or use a finer timer resolution.
Timer settings are not cumulative totals
Each later setting adds only the difference from the previous section total—not from the base. Expose the whole strip first, then cover another section before each subsequent exposure. Do not uncover earlier sections. See the manufacturer’s progressive covering procedure.
Before taking the card into the darkroom
- Keep aperture, filtration, enlarger position, negative and paper unchanged throughout the sequence.
- Prepare and print the report before handling light-sensitive paper. This page is not a safelight.
- The model calculates exposure arithmetic only. It does not control an enlarger, predict print appearance, or compensate for lamp startup, reciprocity, or interrupted-versus-continuous exposure differences.