ND Filter Calculator
Calculate corrected exposure times for any ND filter or filter stack. See the math behind long exposure photography.
1s x 8x (3 stops) = 8s
ND Filter Quick Reference
Corrected exposure times for common base speeds and ND filter strengths.
| Filter | Stops | Factor | 1/125 | 1/60 | 1/30 | 1/15 | 1/8 | 1s | 4s | 15s | 30s |
|---|---|---|---|---|---|---|---|---|---|---|---|
| ND2 | 1 | 2x | 1/60 | 1/30 | 1/15 | 1/8 | 1/4 | 2s | 8s | 30s | 1m |
| ND4 | 2 | 4x | 1/30 | 1/15 | 1/8 | 1/4 | 1/2 | 4s | 16s | 1m | 2m |
| ND8 | 3 | 8x | 1/15 | 1/8 | 1/4 | 1/2 | 1s | 8s | 32s | 2m | 4m |
| ND16 | 4 | 16x | 1/8 | 1/4 | 1/2 | 1s | 2s | 16s | 1m 4s | 4m | 8m |
| ND32 | 5 | 32x | 1/4 | 1/2 | 1s | 2s | 4s | 32s | 2m 8s | 8m | 16m |
| ND64 | 6 | 64x | 1/2 | 1s | 2s | 4s | 8s | 1m 4s | 4m 16s | 16m | 32m |
| ND256 | 8 | 256x | 2s | 4s | 8s | 17s | 32s | 4m 16s | 17m | 1h 4m | 2h 8m |
| ND1000 | 10 | 1024x | 8s | 17s | 34s | 1m 8s | 2m 8s | 17m | 1h 8m | 4h 16m | 8h 32m |
ND Filter Tips
When to use each ND: ND2-ND8 for opening up aperture in bright light (shallow DOF with fast lenses). ND64-ND1000 for long exposures (smooth water, cloud trails, removing people from scenes).
Stacking considerations: Stacking two ND filters adds their stop values together. However, stacking can introduce vignetting (especially on wide-angle lenses), color casts, and reduced sharpness. Keep stacking to two filters maximum.
Variable ND filters: Convenient but less precise. Most variable NDs cover 2-8 stops. They can produce an "X" pattern at maximum density on wide-angle lenses. Best for video work where you need quick adjustments.
Don't forget reciprocity: On film, long exposures beyond 1 second require reciprocity failure compensation. Calculate your ND-corrected time first, then apply the reciprocity correction for your film stock. Check our reciprocity charts for correction values.
