F-number (other)
F-number or F number may refer to: * f-number, the ratio of the lens's focal length to the diameter of the entrance pupil *F number (chemistry) F number is a correlation number used in the analysis of polycyclic aromatic hydrocarbons (PAHs) as a descriptor of their hydrophobicity and molecular size. It was proposed by Robert Hurtubise and co-workers in 1977. Calculation The F number is cal ..., is a number that can be calculated for polycyclic aromatic hydrocarbons from their structure *Fujita scale, a rating of a tornado's intensity by its impact on structures and vegetation *F number in the cross-breeding of hybrid animals such as the Savannah cat, a number that indicates the number of generations of distance from wild stock See also * F-ratio (other) * F scale (other) * function keys (on a computer keyboard, F1, F2, F3, etc.) {{disambiguation ...
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F-number
In optics, the f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture").Smith, Warren ''Modern Optical Engineering'', 4th Ed., 2007 McGraw-Hill Professional, p. 183. It is also known as the focal ratio, f-ratio, or f-stop, and is very important in photography. It is a dimensionless number that is a quantitative measure of lens speed; increasing the f-number is referred to as ''stopping down''. The f-number is commonly indicated using a lower-case hooked f with the format ''N'', where ''N'' is the f-number. The f-number is the reciprocal of the relative aperture (the aperture diameter divided by focal length). Notation The f-number is given by: N = \frac \ where f is the focal length, and D is the diameter of the entrance pupil (''effective aperture''). It is customary to write f-numbers preceded by "", which forms a mathematical expression of the entrance pupil diameter ...
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F Number (chemistry)
F number is a correlation number used in the analysis of polycyclic aromatic hydrocarbons (PAHs) as a descriptor of their hydrophobicity and molecular size. It was proposed by Robert Hurtubise and co-workers in 1977. Calculation The F number is calculated using the formula: :F = B_2 + C_ - \fracR where: : ''B''2 is the number of double bonds : ''C''12 is the number of primary carbon and secondary carbon atoms : ''R'' is the number of non-aromatic rings. Example For fluorene, there are 6 apparent double bonds (three pi bonds in each side benzene-like ring); the central ring has one secondary carbon and is non-aromatic. Therefore: :F = 6 + 1 - \frac1 = 6.5 Correlation It has been found that the F number linearly correlates with the log k' value (logarithm of the retention factor) in aqueous reversed-phase liquid chromatography In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mi ...
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F-ratio (other)
F-ratio or f-ratio may refer to: * The F-ratio used in statistics, which relates the variances of independent samples; see F-distribution * f-ratio (oceanography), which relates recycled and total primary production in the surface ocean * f-number, f-ratio, or focal ratio, the ratio of the focal length of an optical system to the diameter of its entrance pupil See also *F-number (other) F-number or F number may refer to: * f-number, the ratio of the lens's focal length to the diameter of the entrance pupil *F number (chemistry) F number is a correlation number used in the analysis of polycyclic aromatic hydrocarbons (PAHs) as a de ...

F Scale (other)
F scale may refer to: * F-scale (personality test), a personality test that attempts to quantify authoritarian tendencies * Fujita scale, a system of rating of a tornado's intensity by its impact on structures and vegetation * F scale (modelling), a 1:20.3 scaled gauge track used with model trains * F Scale, a validity scale of the Minnesota Multiphasic Personality Inventory * the F major scale. See also * F-number (other) * F-ratio (other) F-ratio or f-ratio may refer to: * The F-ratio used in statistics, which relates the variances of independent samples; see F-distribution * f-ratio (oceanography), which relates recycled and total primary production in the surface ocean * f-numbe ...