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The f-number N is given by: = 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 "f /", which forms a mathematical expression of the entrance pupil's diameter in terms of f and N. [1]
The Fresnel number is a useful concept in physical optics. The Fresnel number establishes a coarse criterion to define the near and far field approximations. Essentially, if Fresnel number is small – less than roughly 1 – the beam is said to be in the far field. If Fresnel number is larger than 1, the beam is said to be near field. However ...
The working f-number is defined by modifying the relation above, taking into account the magnification from object to image: = = (), where N w is the working f-number, m is the lens's magnification for an object a particular distance away, P is the pupil magnification, and the NA is defined in terms of the angle of the marginal ray as before.
Lens speed is the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger than average maximum aperture (that is, a smaller minimum f-number) is called a "fast lens" because it can achieve the same exposure as an average lens with a faster shutter speed. Conversely, a smaller maximum aperture (larger minimum ...
In digital photography, the 35mm-equivalent aperture range is sometimes considered to be more important than the actual f-number. Equivalent aperture is the f-number adjusted to correspond to the f-number of the same size absolute aperture diameter on a lens with a 35mm equivalent focal length. Smaller equivalent f-numbers are expected to lead ...
c °C to f °F: f = c × 1.8 + 32; f °F to k K: k = f + 459.67 / 1.8 k K to f °F: f = k × 1.8 − 459.67; There is also an exact conversion between Celsius and Fahrenheit scales making use of the correspondence −40 °F ≘ −40 °C. Again, f is the numeric value in degrees Fahrenheit, and c the numeric value in degrees Celsius:
A general note applies generally and is not called out with flags. 2. Find number: "FN" meaning "find number" refers to the ordinal number that gives an ID tag to one of the constituents in a parts list (list of materials, bill of materials). Thus "fasten using FN7" refers to a fastener that is "find number" 7 in the list. FoS: feature of size
Guide numbers may be expressed in either of these units of measure: f‑number⋅meters or f‑number⋅feet. Throughout most of the world where the metric system ( SI ) is observed, guide numbers are expressed as a unitless numeric value like 34 , even though they are technically a composite unit of measure that is a two- factor product : f ...