what is meant by the "grade" of an ND filter?

Started Apr 21, 2012 | Discussions thread
jj74e
Senior MemberPosts: 1,633
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Re: what is meant by the "grade" of an ND filter?
In reply to dad_of_four, Apr 22, 2012

dad_of_four wrote:

jj74e wrote:

Oh, so if 16x indicates 4 stops, shouldn't the 32x (which says 5 stops on the product page) and the 64x (which says 6 stops) be 8 stops and 16 stops respectively, not 5 and 6?

Each "Stop" represents 1/2 the light of the previous stop

1 Stop is technically 1/2 the light, but for ND filters, I think they skip this, thus
2 Stops = 1/2 the light
3 Stops = 1/2 * 1/2 the light = 1/4 (or 4x in your case)
3 Stops = 1/2 * 1/2 * 12 = 1/8
4 Stops = 1/2 * 1/2 * 1/2 * 1/2 = 1/16
5 Stops = 1/2 * 1/2 * 1/2 * 1/2 * 1/2 = 1/32
6 Stops = 1/2 * 1/2 * 1/2 * 1/2 * 1/2 * 1/2 = 1/64

oooo i see now, thank you both very much for the help. i wasn't aware the grade actually referred simply to the fraction.

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