Cinematic ND Filter Exposure Guide

Why Do Filmmakers Need an ND Filter Calculator?

Neutral Density filters are sunglasses for your lens — they reduce incoming light without shifting colour, so you can maintain cinematic shutter angles and wide apertures even in bright daylight.

Stops — the language of ND

Every 1 stop halves the light. ND 3 stops = 1/8 of light. ND 6 stops = 1/64. The calculator works entirely in stops so you can compare directly with your filter markings.

What This Calculator Does

Enter your current settings (what the camera sees now) and your target settings (what you want cinematically). The tool computes the stop difference and gives you real-world rounding hints for filters you can actually buy.

Pro Tips

180° rule: For natural motion blur, set shutter angle to 180° (e.g. 24 fps → 1/48 s).
Internal ND: If your camera has built-in ND, enter it here — the tool returns only the external stops you still need.
Rounding: Real filters come in 1/3, 1-stop, and variable ND ranges. Use the More details card to pick a practical value.

ND Filter Shutter Speed Chart & Optical Density

Manufacturers use three naming conventions: ND Factor (e.g., ND8), Optical Density (e.g., 0.9), and Exposure Reduction in Stops (e.g., 3 stops). Use this table to match your calculator results with real-world filters:

ND Factor	Optical Density (OD)	Stops	Light Passing
ND2	0.3	1	50% (1/2)
ND4	0.6	2	25% (1/4)
ND8	0.9	3	12.5% (1/8)
ND16	1.2	4	6.25% (1/16)
ND32	1.5	5	3.125% (1/32)
ND64	1.8	6	1.56% (1/64)
ND1000	3.0	10	0.1% (1/1000)

How to Calculate ND Filter Exposure Manually

Without a calculator, determine the required ND strength by identifying your target cinematic settings and counting the stops of overexposure in ambient light. The core exposure relationship is:

\[ EV = \log_2\left(\frac{N^2}{t}\right) - \log_2\left(\frac{ISO}{100}\right) \]

where N is aperture, t is shutter time in seconds, and the stop difference between current and target EV is the ND strength you need.

ND Filter Stop Calculator for Cinema