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status | not learned | measured difficulty | 37% [default] | last interval [days] | |||
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repetition number in this series | 0 | memorised on | scheduled repetition | ||||

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tio in telescopes 6 Working f-number 7 History 7.1 Origins of relative aperture 7.2 Aperture numbering systems 7.3 Typographical standardization 8 See also 9 References 10 External links Notation[edit] The f-number N is given by: <span>where is the focal length, and is the diameter of the entrance pupil (effective aperture). It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the entrance pupil diameter in terms of f and N. [2] For example, if a lens's focal length is