Cristian Diaz Posted December 11, 2018 Share Posted December 11, 2018 Hi all! What does the 3 stand for when speaking of ND filters? I know each increase in multiple signifies a 1 f-stop, but never stopped to think why a 3 increase... Thanks... Link to comment Share on other sites More sharing options...
Mark Dunn Posted December 11, 2018 Share Posted December 11, 2018 (edited) It's actually 0.3, abbreviated to 3. Photographic density is measured on a logarithmic, not a linear, scale, and 0.3 is the base 10 logarithm of 2. So an increase, or reduction of 0.3 in density represents a factor of 2,or one stop. Edited December 11, 2018 by Mark Dunn Link to comment Share on other sites More sharing options...
Max Field Posted December 11, 2018 Share Posted December 11, 2018 This is the most valuable link I return to when double checking things https://en.wikipedia.org/wiki/Neutral-density_filter#ND_filter_ratings Link to comment Share on other sites More sharing options...
Mark Dunn Posted December 11, 2018 Share Posted December 11, 2018 The Wiki page is handy as a reference, but OP asked why the figure is 0.3. That table contains some infelicities and doesn't explain log density. Link to comment Share on other sites More sharing options...
Cristian Diaz Posted December 23, 2018 Author Share Posted December 23, 2018 Thank you all for your insight. Link to comment Share on other sites More sharing options...
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