How do ND filters work?

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.

Can I stack ND filters?

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.

What is reciprocity failure?

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.

Do I need a cable release?

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.

PhotoCalcs

Long Exposure Calculator \u2014 ND Filter Compensation

Calculate adjusted shutter speed when using ND filters for long exposures.

Base Shutter Speed

Shutter speed / exposure time

ND Filter

Neutral density filter strength

Stack a second filter

Add a second ND filter

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\u20130.5 depending on the film stock.

Frequently Asked Questions

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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.