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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.
Defining equation SI units Dimension ... f = lens focal length; x 1 = object distance; x 2 = image distance; r 1 = incident curvature radius; r 2 = refracted ...
The focal length, f, of a lens in air is given by the lensmaker's equation: = [+ ()], where n is the index of refraction of the lens material, and R 1 and R 2 are the radii of curvature of the two surfaces.
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.
Similarly to curved mirrors, thin lenses follow a simple equation that determines the location of the images given a particular focal length and object distance (): + = where is the distance associated with the image and is considered by convention to be negative if on the same side of the lens as the object and positive if on the opposite side ...
Gaussian optics applies to systems in which all the optical surfaces are either flat or are portions of a sphere. In this case, simple explicit formulae can be given for parameters of an imaging system such as focal length , magnification and brightness, in terms of the geometrical shapes and material properties of the constituent elements.
The original application called for placing the chart at a distance 26 times the focal length of the imaging lens used. The bars above and to the left are in sequence, separated by approximately the square root of two (12, 17, 24, etc.), while the bars below and to the left have the same separation but a different starting point (14, 20, 28, etc.)
To make the linear dispersion of the system zero, the system must satisfy the equations ... for a lens with focal length. Solving these two ...