Long Exposure — ND Exposure Calculation

Method

1. Baseline (Sunny 16). In bright sun without filters: ISO 100, f/16, 1/100 s (shutter ≈ 1/ISO).

2. Add the ND's stops. An ND1000 (ND10) is 10 stops (~1000×), so lengthen the shutter by 10 stops from the baseline:

Stops added	Shutter
+1	1/50 s
+2	1/25 s
+3	1/13 s
+4	1/6 s
+5	1/3 s
+6	0.6 s
+7	1.3 s
+8	2.5 s
+9	5 s
+10	10 s

So ISO 100, f/16, ND1000 → ~10 s.

3. Trade off aperture/ISO. Want shallower DOF or less blur? Opening to f/8 (+2 stops) or raising to ISO 400 (+2 stops) each shortens the shutter to ~2.5 s. Stay at f/16, ISO 100 for the longest, silkiest motion.

Common NDs (bright day, ISO 100, f/16)

ND	Stops	Shutter
ND8	3	1/13 s
ND64	6	0.6 s
ND1000	10	10 s

Field notes

Tripod is essential for anything slower than ~1/30 s. Use a 2-sec Self-timer or remote to avoid shake, cover the viewfinder against light leaks, and shoot RAW for recovery latitude.

Consolidated from notes: 5 Sep 2025 (40mm + ND filter exposure calculation)