Neutral density & exposure

There are probably online calculators or Apps for this, but when I’m in the field I prefer just to have a couple of printed pages where I can see the exposure to use at a glance. See here for the PDF and a far more complete version of the table below.

A typical set of Neutral Density filters consists of an ND2, ND4 and an ND8 filter which can be combined and, if combined, the resulting ND number is the multiplication of the ND numbers of the filters used. For example: Combining the ND2, ND4 and ND8 filter will result in an ND64 filter: 2x4x8=64.

Use your exposure meter (TTL or external) to get the base exposure time and then apply the filter(s) to the lens. Find the base exposure in the first column in the table below to get the exposure time to use for the ND number of the filter(s) on the lens and then apply the correction for the Reciprocity Failure of the film that you are using, if applicable. Typically this information is provided by the manufacturer of the film and usually available for download in PDF form from their site, but also see here for more details. The easiest is when the Reciprocity Failure correction is expressed in added stops so you can just use the table to skip to the correct line.

Exposure ND2 ND4 ND8 ND16 ND32
1/60 1/30 1/15 1/8 1/4 1/2
1/50 1/25 1/12 1/6 1/3 2/3
1/40 1/20 1/10 1/5 2/5 4/5
1/30 1/15 1/8 1/4 1/2 1
1/25 1/12 1/6 1/3 2/3 1 1/3
1/20 1/10 1/5 2/5 4/5 1 3/5
1/15 1/8 1/4 1/2 1 2
1/12 1/6 1/3 2/3 1 1/3 2 2/3
1/10 1/5 2/5 4/5 1 3/5 3 1/5
1/8 1/4 1/2 1 2 4
1/6 1/3 2/3 1 1/3 2 2/3 5 1/3
1/5 2/5 4/5 1 3/5 3 1/5 6 2/5
1/4 1/2 1 2 4 8
1/3 2/3 1 1/3 2 2/3 5 1/3 10 2/3
2/5 4/5 1 3/5 3 1/5 6 2/5 12 4/5
1/2 1 2 4 8 16
2/3 1 1/3 2 2/3 5 1/3 10 2/3 21 1/3
0.8 1 3/5 3 1/5 6 2/5 12 4/5 25 3/5
1 2 4 8 16 32
1 1/3 2 2/3 5 1/3 10 2/3 21 1/3 42 2/3
1 3/5 3 1/5 6 2/5 12 4/5 25 3/5 51 1/5
2 4 8 16 32 64
2 2/3 5 1/3 10 2/3 21 1/3 42 2/3 85 1/3
3 1/5 6 2/5 12 4/5 25 3/5 51 1/5 102 2/5
4 8 16 32 64 128

I realize that if the table gives you an exposure time of 6826 and 2/3 of a second, the 2/3 of a second isn’t really going to make a difference but Excel insisted 🙂

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