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The focal point F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror.. The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power.
This is a unit of fame, hype, or infamy, named for the American puzzle creator and editor, Will Shortz. The measure is the number of times one's name has appeared in The New York Times crossword puzzle as either a clue or solution. Arguably, this number should only be calculated for the Shortz era (1993–present).
If the medium surrounding an optical system has a refractive index of 1 (e.g., air or vacuum), then the distance from each principal plane to the corresponding focal point is just the focal length of the system. In the more general case, the distance to the foci is the focal length multiplied by the index of refraction of the medium.
A 100 mm focal length f /4 lens has an entrance pupil diameter of 25 mm. A 100 mm focal length f /2 lens has an entrance pupil diameter of 50 mm. Since the area is proportional to the square of the pupil diameter, [6] the amount of light admitted by the f /2 lens is four times that of the f /4 lens.
A crossword (or crossword puzzle) is a word game consisting of a grid of black and white squares, into which solvers enter words or phrases ("entries") crossing each other horizontally ("across") and vertically ("down") according to a set of clues. Each white square is typically filled with one letter, while the black squares are used to ...
The abbreviation is not always a short form of the word used in the clue. For example: "Knight" for N (the symbol used in chess notation) Taking this one stage further, the clue word can hint at the word or words to be abbreviated rather than giving the word itself. For example: "About" for C or CA (for "circa"), or RE.
In optics, an afocal system (a system without focus) is an optical system that produces no net convergence or divergence of the beam, i.e., has an infinite effective focal length. [1] This type of system can be created with a pair of optical elements where the physical distance d between the elements is equal to the sum of each element's focal ...
The number of words in the answer is not given in the clue—so a one-word clue can have a multiple-word answer. [28] The theme, if any, will be applied consistently throughout the puzzle; e.g., if one of the theme entries is a particular variety of pun, all the theme entries will be of that type. [9]