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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 Y level or wye level is the oldest and bulkiest of the older style optical instruments. A low-powered telescope is placed in a pair of clamp mounts, and the instrument then leveled using a spirit level, which is mounted parallel to the main telescope. The term dumpy level (also builder's level) endures despite the evolution in design. They ...
The design of photographic lenses for use in still or cine cameras is intended to produce a lens that yields the most acceptable rendition of the subject being photographed within a range of constraints that include cost, weight and materials.
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]
Such a blur spot has the same shape as the lens aperture, but for simplicity, is usually treated as if it were circular. In practice, objects at considerably different distances from the camera can still appear sharp; [1] the range of object distances over which objects appear sharp is the depth of field (DoF). The common criterion for ...
In a digital camera, diffraction effects interact with the effects of the regular pixel grid. The combined effect of the different parts of an optical system is determined by the convolution of the point spread functions (PSF). The point spread function of a diffraction limited circular-aperture lens is simply the Airy disk. The point spread ...
The eye-level finder is an evolution of the waist-level finder, using a roof pentaprism or pentamirror to correct the image while making it viewable through an eyepiece at the rear of the camera. Some digital cameras have an articulating screen or a swivel lens , this allows the screen to be angled to make it viewable at waist-level.