## About ND Filter Calculator (Formula)

Certainly! An ND (Neutral Density) filter is used in photography to reduce the amount of light entering the camera lens. This can be especially useful when a photographer wants to use a slower shutter speed in bright conditions, for effects such as motion blur in moving water, or when a wider aperture is desired for a shallower depth of field.

**Formula:**

**FS=BS∗2n**

Where:

- $FS$ is the Final Shutter Speed after applying the ND filter.
- $BS$ is the Base Shutter Speed, i.e., the shutter speed without using the ND filter.
- $n$ is the stop value of the ND filter.

**Explanation:**

Each “stop” in photography refers to a halving or doubling of the amount of light. So when you add an ND filter with a stop value of $n$, you’re reducing the light by a factor of $_{n}$.

For example, if your base shutter speed is 1/100s (or just 100 when using the calculator) and you use an ND8 filter, which reduces light by 3 stops ($_{3}=8$), your new shutter speed should be 8 times longer than the base speed. So:

**FS=100×2cube**

**Common ND Filters and Their Stop Values:**

- ND2: 1 stop
- ND4: 2 stops
- ND8: 3 stops
- ND16: 4 stops
- ND32: 5 stops
- ND64: 6 stops
- ND128: 7 stops … and so on.

It’s essential to understand that the actual numeric value of the ND filter (like ND8, ND64, etc.) represents the factor by which light is reduced. The corresponding stop value is the logarithm base 2 of that number. For instance, ND8 reduces light by a factor of 8, which corresponds to 3 stops (since $_{3}=8$).

**Usage:**

This formula and calculator can be beneficial for photographers who want to understand how their shutter speed will change when using an ND filter. This knowledge can help them achieve desired artistic effects while maintaining correct exposure.