Talk:Numerical aperture

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The two definitions should be merged into a single page, replacing this disambiguation page. The definitions are all fundamentally the same--the NA formula for a fiber in terms of the indices of refraction theoretically should be the same as the NA as defined by the acceptance angle of the fiber (which would be the "correct" optical definition). Unfortunately, it seems that the federal government has confused this in their standards, making the approximate theoretical formula the definition of NA for optical fibers. This ambiguity could all be addressed in a single page.--Srleffler 06:48, 16 November 2005 (UTC)

[edit] symbolic syntax

Is it so common to write out f/# as a variable name? I took a class and we used , which seems more like usual mathematical conventions. Potatoswatter 22:58, 13 March 2007 (UTC)

f/# is by far the most common notation, and is officially the standard notation in photography (e.g. ASA standard PH2.12-1961 American Standard General-Purpose Photographic Exposure Meters). Note, though, that this notation is not a variable name in the usual sense, which helps to explain its odd form. One writes that the f-number of a camera lens is f/2.5, not that some variable equals 2.5. Additionally, though it looks like a fraction it is best not thought of that way since when one writes f/2.5 one means that the f-number is 2.5, not that one should consider the focal length divided by 2.5 (which would be the diameter of the entrance pupil).

If one is doing a lot of mathematics with f-numbers in a science or engineering class, it is convenient to assign a more conventional variable. N is commonly used, but seems like a good notation as well.

The notation is discussed at f-number#Notation, and there is a brief description of the history of this odd notation at f-number#Typographical standardization.--Srleffler 03:51, 14 March 2007 (UTC)