PhotoCalcs
Long Exposure Calculator — ND Filter Compensation
Calculate adjusted shutter speed when using ND filters for long exposures.
Add a second ND filter
Use a cable release for exposures over 1 second. Lock mirror up to reduce vibration.
How We Calculate This
Adjusted exposure = base shutter speed × 2^(ND stops)
Each stop of ND doubles the required exposure time. A 10-stop ND filter multiplies the exposure by 2^10 = 1024.
Reciprocity correction (film only): corrected = calculated^(1 + factor)
where the factor is typically 0.1–0.5 depending on the film stock.
Frequently Asked Questions
ND (Neutral Density) filters reduce the amount of light entering the lens without affecting colour. Each stop of ND halves the light, requiring a proportional increase in exposure time. An ND1000 (10-stop) filter turns a 1/125s exposure into an 8-second exposure.
Yes, stacking adds the stop values together. An ND8 (3 stops) plus an ND1000 (10 stops) gives 13 stops total. However, stacking can introduce vignetting on wide-angle lenses and slight colour casts. Use high-quality filters to minimise issues.
Film does not respond linearly to light at very long exposures (typically over 1 second). The actual exposure needed is longer than calculated. Each film stock has a different reciprocity factor. Digital sensors do not suffer from reciprocity failure.
For exposures longer than 1/15s, a cable release or remote shutter prevents camera shake. For bulb mode exposures (over 30s), you must hold the shutter open with a locking cable release or use a timed remote.
Related Calculators
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Reciprocity Failure Calculator
Calculate corrected film exposure times for reciprocity failure at long exposures. Covers Ilford, Kodak, and Fuji film stocks with Schwarzschild correction.
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Compensate for reciprocity failure when shooting long exposures on film. Enter metered time and film stock for corrected exposure. Free calculator.
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Last updated: March 2026
All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.