ND Filter Calculator
Calculate adjusted long exposure shutter speeds when mounting Neutral Density (ND) filters for smooth water, moving clouds, and cinematic video.
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How ND Filter Light Reduction is Calculated
Neutral density filters act as sunglasses for your camera lens. Each stop of ND cuts the light entering the camera in half ($2^n$), requiring the shutter to stay open twice as long:
The ND Shutter Formula
New Shutter Speed = Base Shutter Speed × 2^(Total Stops)
Example: 1/125s base speed with a 10-stop ND filter = (1/125) × 2^10 = 1024 / 125 ≈ 8.2 seconds.
Why Autofocus Fails with 10-Stop Filters
A 10-stop ND filter blocks 99.9% of incoming light. Camera autofocus sensors and optical viewfinders become completely black. Always compose your frame and lock manual focus before mounting the ND filter glass onto your lens.
Frequently Asked Questions
What is the difference between ND8, ND64, and ND1000?
The number represents the light attenuation factor: ND8 cuts light by 2^3 (3 stops), ND64 cuts light by 2^6 (6 stops), and ND1000 cuts light by 2^10 (10 stops).
Why do waterfalls look silky with ND filters?
Waterfalls and ocean surf move continuously. An exposure longer than 0.5 to 2 seconds blurs individual droplets into a smooth, ethereal mist.
Why do cheap ND filters create purple or magenta color casts?
Standard glass absorbs visible light but transmits invisible infrared (IR) light. High-end filters feature IR-blocking coatings to prevent red/magenta tinting on digital sensors.