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How strong is my ND filter?

Neutral density filters, also known as ND filters, are essential tools for any photographer or videographer. They’re designed to reduce the amount of light entering the camera lens without affecting the color of the image. ND filters come in different strengths, and each strength reduces the light by a specific amount.

The degree of light blocking is often referred to in terms of the number of ‘stops of light’ the filter blocks. For each ‘stop’ of light blocked, the exposure time doubles. An alternate terminology uses exponential values of the number ‘2’ to reflect this principle. Yet another system uses values of 0.3 to designate 1 stop of light blocking.

For instance, an ND filter that blocks 2 stops of light can be called a ‘2 stop’ ND filter. Using the alternative terminology, it can also be called an ND4 filter (2^2 =4) or an ND 0.6 filter (0.3X2 =0.6). This terminology also applies to the strength of GND (graduated neutral density) filters.

To choose the right strength of ND filter, you need to consider the lighting conditions and the effect you want to achieve. If you’re shooting in bright sunlight and want to achieve a shallow depth of field, you might need a higher-strength ND filter like ND8 or ND16. If you’re shooting waterfalls or other moving water, you might need a lower-strength ND filter like ND2 or ND4 to create a smooth, silky effect.

Choosing the right strength of ND filter depends on the lighting conditions and the effect you’re trying to achieve. Here are the most common ND filter strengths and their corresponding light reduction:

ND20.31 STOPS50%
ND40.62 STOPS25%
ND80.93 STOPS12.5%
ND161.24 STOPS6.25%
ND321.55 STOPS3.12%
ND641.86 STOPS1.56%
ND1282.17 STOPS0.78%
ND2562.48 STOPS0.39%
ND5002.79 STOPS0.2%
ND10003.010 STOPS0.1%
ND20003.311 STOPS0.05%
ND320004.515 STOPS0.003%
ND100K6.020 STOPS0.0001%