ND filter calculator
Find the ND you need to shoot at your chosen stop. Enter what the meter reads and the stop you want; the calculator gives the ND in optical density, the light cut in stops, the filter factor and how much light is transmitted.
Results round to the nearest third of a stop, the smallest ND step. When the exact value falls between standard 0.3-step filters, it tells you how far over or under each nearby filter leaves you.
How to use it
- Meter reads: the stop from your light meter at your ISO and shutter.
- You want to shoot at: the stop you want on the lens.
- Keep ISO and shutter the same as the reading.
Example
The meter reads T8 and you want to shoot at T2.8. That is 3 stops too much light: use ND 0.9, a filter factor of ×8 that passes 12.5% of the light.
Good to know
Optical density 0.3 cuts one stop, 0.6 two stops, 0.9 three stops. Stacking filters adds their densities.