Editing Binary logarithm (section)

===Photography===
In [[photography]], [[exposure value]]s are measured in terms of the binary logarithm of the amount of light reaching the film or sensor, in accordance with the [[Weber–Fechner law]] describing a logarithmic response of the human visual system to light. A single stop of exposure is one unit on a base-{{math|2}} logarithmic scale.<ref>{{citation|title=The Manual of Photography|first1=Elizabeth|last1=Allen|first2=Sophie|last2=Triantaphillidou|publisher=Taylor & Francis|year=2011|isbn=978-0-240-52037-7|page=228|url=https://books.google.com/books?id=IfWivY3mIgAC&pg=PA228}}.</ref><ref name="btzs">{{citation|title=Beyond the Zone System|first=Phil|last=Davis|publisher=CRC Press|year=1998|isbn=978-1-136-09294-7|page=17|url=https://books.google.com/books?id=YaVEAQAAQBAJ&pg=PA17}}.</ref> More precisely, the exposure value of a photograph is defined as
:<math>\log_2 \frac{N^2}{t}</math>
where {{mvar|N}} is the [[f-number]] measuring the [[aperture]] of the lens during the exposure, and {{mvar|t}} is the number of seconds of exposure.<ref>{{harvtxt|Allen|Triantaphillidou|2011}},  [https://books.google.com/books?id=IfWivY3mIgAC&pg=PA235 p.&nbsp;235].</ref>

Binary logarithms (expressed as stops) are also used in [[densitometry]], to express the [[dynamic range]] of light-sensitive materials or digital sensors.<ref>{{citation|title=Visual Effects Society Handbook: Workflow and Techniques|first1=Susan|last1=Zwerman|first2=Jeffrey A.|last2=Okun|publisher=CRC Press|year=2012|isbn=978-1-136-13614-6|page=205|url=https://books.google.com/books?id=3rLpAwAAQBAJ&pg=PA205}}.</ref>