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Thin lens. A lens may be considered a thin lens if its thickness is much less than the radii of curvature of its surfaces (d ≪ |R1| and d ≪ |R2|). In optics, a thin lens is a lens with a thickness (distance along the optical axis between the two surfaces of the lens) that is negligible compared to the radii of curvature of the lens surfaces.
Focal length. Measure of how strongly an optical system converges or diverges light. 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 ...
A similar sort of eyeglass lens is the myodisc, sometimes termed a minus lenticular lens, used for very high negative corrections. More aesthetic aspheric lens designs are sometimes fitted. [ 3 ] A film made of cylindrical lenses molded in a plastic substrate as shown in above picture, can be applied to the inside of standard glasses to correct ...
Vertex distance. Vertex distance. Vertex distance is the distance between the back surface of a corrective lens, i.e. glasses (spectacles) or contact lenses, and the front of the cornea. Increasing or decreasing the vertex distance changes the optical properties of the system, by moving the focal point forward or backward, effectively changing ...
In number theory, the optic equation is an equation that requires the sum of the reciprocals of two positive integers a and b to equal the reciprocal of a third positive integer c: [1] {\displaystyle {\frac {1} {a}}+ {\frac {1} {b}}= {\frac {1} {c}}.} Multiplying both sides by abc shows that the optic equation is equivalent to a Diophantine ...
The aim of an accurate intraocular lens power calculation is to provide an intraocular lens (IOL) that fits the specific needs and desires of the individual patient. The development of better instrumentation for measuring the eye's axial length (AL) and the use of more precise mathematical formulas to perform the appropriate calculations have significantly improved the accuracy with which the ...
13 – Prism scale knob. A lensmeter or lensometer (sometimes even known as focimeter or vertometer), [1][2] is an optical instrument used in ophthalmology. It is mainly used by optometrists and opticians to measure the back or front vertex power of a spectacle lens and verify the correct prescription in a pair of eyeglasses, to properly orient ...
Astigmatism (optical systems) An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- (a ...
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