ND Stop → Shutter Speed Converter

This ND filter shutter speed calculator takes the shutter speed your meter reads without the neutral density filter, then the filter's strength in stops. The calculator multiplies the exposure time by 2^stops — e.g. 1/125 s + a 10-stop ND 1000 → 8 s.

Metered shutter (no filter)

…or type any shutter (1/250, 0.5, 2.5)

ND strength (stops)

…or pick a named filter

How the math works

Each stop of ND halves the light, so exposure time doubles per stop: t_new = t_base × 2^stops. A filter's stop value comes from its ND number: stops = log₂(ND number) — ND8 = 3 stops, ND64 = 6 stops, ND1000 ≈ 10 stops (9.97). Optical density (OD) is log₁₀(ND), so an "ND3.0" filter = 10 stops.

Bulb Countdown Timer

For exposures longer than 30 s your camera needs Bulb mode for the bulb exposure. Set the computed exposure time, press start, and the timer beeps during the last 3 seconds and at the end — no phone app or intervalometer app needed. Timing is timestamp-based, so it stays accurate even if you switch browser tabs.

Minutes

Seconds

Audio cues

00:08.0

Ready. Set a time and press Start.

Honest scope: this is a manual bulb timer for exposures up to a few minutes. For exposures over ~5 minutes a hardware intervalometer or tethered app is more reliable (sensor heat and battery, not the math, become the limit).

Stacked ND Filter Calculator

Screwing two filters together? Stops add up: ND8 (3 stops) + ND64 (6 stops) = 9 stops total. Tap filters to stack them, or type a custom ND number.

Custom ND number (e.g. 1000)

…or optical density (e.g. 3.0)

0 stops

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ND Filter Chart — Number ↔ Stops ↔ Optical Density ↔ Transmission

The complete ND filter conversion chart: filter number, stop value, optical density (OD), and how much light gets through. Use it as an ND filter stops chart, density chart, or factor chart.

Filter (ND no.)	Stops	Optical density	Transmission	Common name

Film Reciprocity Failure Compensator

Film loses effective speed during long exposures ("reciprocity failure") — a metered 10 s can need 20–40 s of real exposure depending on the film. Compensation curves below come from the manufacturers' own datasheets (Ilford, Kodak, Fujifilm); intermediate values are interpolated on a log–log scale.

Film stock

Metered exposure (seconds, e.g. 10 or 1/2)

Compensation table — film

Metered	Shoot this	Extra stops

Reality check: datasheet curves are starting points. Actual reciprocity varies with film batch, temperature, developer and agitation — bracket one stop over and under for critical shots. Long exposures also raise contrast; many photographers pull development slightly (N−1).

Exposure Triangle Rebalancer

You add an ND filter but want to keep one setting fixed? Pick your base exposure and the ND strength — the tool shows all three equivalent options: lock the aperture, lock the shutter, or lock the ISO.

Shutter

Aperture (f/)

ISO

ND stops added

🔒 Lock aperture

Keep f/8, ISO 100

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🔒 Lock shutter

Keep 1/125, ISO 100

–

🔒 Lock shutter + aperture

Keep 1/125, f/8

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Video & Drone ND Mode — the 180° Shutter Rule

Cinematic motion blur needs shutter speed ≈ 1 ÷ (2 × frame rate) — the 180° shutter rule. At 24 fps that's 1/48 s (≈1/50), at 60 fps it's 1/120 s. In bright light the only way to hold that shutter without blowing out is an ND filter — which is why drone pilots (fixed f/2.8 aperture!) live on NDs.

Frame rate

Your correct exposure WITHOUT ND is at shutter…

Shutter angle calculator

Shutter angle = 360° × shutter time × fps. Check what angle any shutter/fps combo really is:

Shutter (e.g. 1/50)

Frame rate

Drone quick presets

Most DJI drones (Mini, Air, Mavic) have a fixed f/2.8–f/1.7 aperture — ND filters are the only exposure control besides shutter and ISO. Pick a preset above for the target shutter, then read the ND you need.

Exposure Bracketing Planner (HDR)

Plan an HDR bracket: base shutter, step size, frame count → the exact shutter sequence.

Base shutter

Step (EV)

Frames (odd)

Multiple Exposure Averaging

Stacking N identical frames in-camera (or averaging in post)? Each frame must be underexposed so the sum stays correct:

Number of exposures

Night Sky Helpers

🌕 Moon — Looney 11 rule

The moon is sunlit: shoot at f/11, shutter = 1/ISO. (Gibbous/crescent: open ~1 stop.)

ISO

✨ Milky Way — 500 rule

Longest shutter before stars trail: 500 ÷ (focal length × crop factor). (Newer NPF rule is stricter; 500 is the classic field starting point.)

Focal length (mm)

Crop factor (1 = full frame)

📷 Pinhole exposure

Pinhole f-number = focal length ÷ pinhole diameter. Exposure scales with the square of the f-number ratio.

Metered shutter at

Metered aperture f/

Pinhole focal length (mm)

Pinhole diameter (mm)

💡 Lux → Exposure Value

From a light-meter lux reading to EV at ISO 100 (approximation, ±½ EV): EV₁₀₀ ≈ log₂(lux × 100 / 320), anchored to Sunny 16 (100,000 lux ≈ EV 15).

Illuminance (lux)

Methodology & data sources

Stop math: t_new = t_base × 2^stops; stops = log₂(ND number); optical density = log₁₀(ND). Stacked filters add stops. Standard shutter/aperture/ISO scales snap to ⅓-stop values.
Reciprocity data: Ilford HP5 Plus: adjusted = metered^1.31 beyond ½ s; Ilford FP4 Plus: metered^1.26 beyond ½ s (Ilford datasheets). Kodak Tri-X 400: 1 s→2×, 10 s→4×, 100 s→8× (Kodak F-4017), power-law interpolated. Kodak T-Max 100: 10 s→15 s, 100 s→200 s; T-Max 400: 10 s→15 s, 100 s→300 s (Kodak F-4016), log–log interpolated. Fujifilm Neopan 100 Acros: no compensation below 120 s, +½ stop for 120–1000 s (Fuji datasheet).
180° rule: Target shutter = 1 ÷ (2 × fps); shutter angle = 360° × shutter × fps.
Lux → EV: EV₁₀₀ ≈ log₂(lux × 100 / 320), calibrated so 100,000 lux ≈ EV 15 (Sunny 16).
Privacy: Every calculation runs in your browser. No accounts, no cookies, no network requests — verify with your browser's dev tools.

ND Filter Exposure Calculator & Long Exposure Suite