7
Stops of light reduction
2.1
Optical density (ND x.x)
0.7812%
Light transmitted
×128
Exposure time multiplier
ND128 exposure conversion#
Meter without the filter, then multiply the shutter time by 128.
| Without filter | With ND128 |
|---|---|
| 1/4000 s | 1/31 s |
| 1/2000 s | 1/16 s |
| 1/1000 s | 1/7.8 s |
| 1/500 s | 1/3.9 s |
| 1/250 s | 0.5 s |
| 1/125 s | 1 s |
| 1/60 s | 2.1 s |
| 1/30 s | 4.3 s |
| 1/15 s | 8.5 s |
| 1/8 s | 16 s |
| 1/4 s | 32 s |
| 0.5 s | 64 s |
| 1 s | 128 s |
| 2 s | 256 s |
ND calculator & countdown timer#
Shutter speed with filter—
Light reduction—
0:00
What a ND128 filter is for#
ND128 (also sold as ND 2.1 or “7-stop”) is typically used for: Silky waterfalls and seascapes in daylight; streaking clouds.
For video: in bright sun at f/2.8 and ISO 100 you need about 6.4 stops of ND to shoot at 1/50 s (the 180° shutter rule at 25 fps). This filter alone is enough.
Tips: compose and focus before attaching dark filters, cover the viewfinder eyepiece on DSLRs to stop light leaks, and expect a colour cast with strong NDs — shoot RAW and set white balance afterwards.
Other ND strengths#
Frequently asked questions#
How many stops is a ND128?
7 stops — it passes 1/128 of the light (density 2.1).
What shutter speed with a ND128 filter?
Multiply your unfiltered shutter speed by 128. For example 1/125 s becomes 1 s.
Last updated October 03, 2026 · How we calculate · Sources