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  5. How strong is my ND filter?

How strong is my ND filter?

The degree of light blocking is often referred to in terms of the number of ‘stops of light’ which 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 which 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.

 

 

NDOptical DensityF-stop ReductionTransmittance %
ND20.31 Stop50%
ND40.62 Stop25%
ND80.93 Stop12.5%
ND161.24 Stop6.25%
ND321.55 Stop3.12%
ND641.86 Stop1.56%
ND1282.17 Stop0.78%
ND2562.48 Stop0.39%
ND5002.79 Stop0.2%
ND10003.010 Stop0.1%
ND20003.311 Stop0.005%
ND320004.515 Stop0.003%
ND1000K6.020 Stop0.0001%