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Lens and ray diagram for calculating the circle of confusion diameter c for an out-of-focus subject at distance S 2 when the camera is focused at S 1. The auxiliary blur circle C in the object plane (dashed line) makes the calculation easier. An early calculation of CoC diameter ("indistinctness") by "T.H." in 1866.
The circular bubble is used to roughly level the instrument in two dimensions. The plate level is then used, rotating it 90 degrees between readings to level the instrument more precisely. The Fell All-Way precision level, one of the first successful American made bull's eye levels for machine tool use, was invented by William B. Fell, Rockford ...
If the bubble housing has graduated divisions, then the sensitivity is the angle or gradient change that moves the bubble by one of these divisions. 2 mm (0.079 in) is the usual spacing for graduations; on a surveyor's level, the bubble will move 2 mm (0.079 in) when the vial is tilted about 0.005 degree.
The f-number of the human eye varies from about f /8.3 in a very brightly lit place to about f /2.1 in the dark. [17] Computing the focal length requires that the light-refracting properties of the liquids in the eye be taken into account. Treating the eye as an ordinary air-filled camera and lens results in an incorrect focal length and f-number.
Very-large-aperture lenses designed to be useful in very low light conditions with apertures ranging from f/1.2 to f/0.9 are generally restricted to lenses of standard focal length because of the size and weight problems that would be encountered in telephoto lenses and the difficulty of building a very wide aperture wide angle lens with the ...
where θ is the angular resolution , λ is the wavelength of light, and D is the diameter of the lens' aperture. The factor 1.22 is derived from a calculation of the position of the first dark circular ring surrounding the central Airy disc of the diffraction pattern. This number is more precisely 1.21966989...
The number 1/1730 derives from a circle of confusion diameter of 0.025 mm on a full-frame 35 mm film format, with diagonal size about 43.25 mm (43.25/0.025 is 1730). The CoC size of 0.025 mm for this format appears in Jacobson's Photographic Lenses Tutorial, [1] and the 1730 in his 1996 Photographic Lenses FAQ. [2]
The green filter factor of 4 yields a 2 f-stop light reduction. The filter factor, given the exposure change in f-stops, may be calculated using the formula: 2 f s t o p = f i l t e r f a c t o r {\displaystyle 2^{fstop}=filterfactor}