Long Exposure ND Filter Stack Calculator

Method, formula and assumptions

Stop reductions add, so exposure multiplier = 2^(filter1 + filter2). Multiply the metered unfiltered time by that factor. Sequence duration adds one interval between successive exposures, not after the last.

Input definitions and supported units

• Unfiltered exposure (seconds): Measured or assumed numerical value, from 0.000001 to 10000; must be positive.
• First filter reduction (stops): Measured or assumed numerical value, from 0 to 20; zero is supported where the stated method permits it.
• Second filter reduction (stops): Measured or assumed numerical value, from 0 to 20; zero is supported where the stated method permits it.
• Camera interval after each exposure (seconds): Measured or assumed numerical value, from 0 to 10000; zero is supported where the stated method permits it.
• Frames to capture: Whole-number count, from 1 to 100000; must be positive.

Worked example with answer

An unfiltered 1/8 second with 6-stop and 3-stop filters needs 9 stops, a 512x factor and 64 seconds. Five frames with 2-second gaps take 328 seconds.

How to use the results

Meter the base exposure with the intended aperture and ISO. This tool also checks the time commitment of repeated long exposures.

Results retain full precision internally and display up to four decimal places. Very small nonzero results use scientific notation rather than appearing as zero. Check the labels before comparing values across units.

Limitations and references

Actual filter density, color casts, vignetting, changing light and reciprocity behavior can change exposure. It does not guarantee image brightness or stacking compatibility.

The method is a self-contained arithmetic, geometric or explicitly stated mathematical model. There are no imported tariffs, empirical presets or equipment specifications; measured values and allowances must come from your own process.

Related planning tools

• Exposure Bracket Sequence Budget Calculator
• Equivalent Exposure Triangle Calculator

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