![]() hold for the radius of the beam waist at a focus behind some lens with a given focal length (see below), or the possible magnification of a telescope containing that optical system.Ī common (but not universally used) approach for the definition of focal lengths of extended systems is based on geometrical optics.įor finding the front focal point, one calculates rays which are horizontal on the back side (see Figure 2), using the paraxial approximation. the entrance or the middle) could be used, but that would in general mean that some common rules can not be applied, which e.g. In principle, an arbitrary definition of a reference point (e.g. It is not obvious how to define the focal length of an extended system – there are different possibilities!įor an optical system, which may consist of multiple lenses and other optical elements, the above definition of the focal length cannot be used, as it is not clear a priori for an extended system where to measure the distance to the focus: from the entrance into the optical system, from the exit, the middle, or some other position? Focal Length of an Extended Optical System The fabrication of dielectric mirror coatings can be more difficult for very strongly curved mirror substrates, but with refined techniques it is possible to reach focal lengths of only a few millimeters, as required for some miniature lasers. After you have modified some values, click a "calc" button to recalculate the field left of it.Īttention: The buttons do not work, as Javascript is turned off in your browser!Ĭurved laser mirrors usually have a curvature radius somewhere between 10 mm and 5 m. Calculator for Focal Length of a Curved Mirror Radius of curvature:Įnter input values with units, where appropriate. ![]()
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