Conventionally, we set up lens diagrams with light going left to right, where distance to the left of the lens is negative and distance to the right of the lens is positive. See Picture 3. Therefore, `r_1` is positive and `r_2` is negative. length of the lens is called the lensmaker's equation, since it gives the focal length in terms of This equation is used for determining the focal length of a thin lens (thickness = 0) with radii of curvature r1 and r2. Lensmaker Equation is used to determine whether a lens will behave as a converging or Let's say that the magnitude of each radius of curvature is 2. Basically, it's the distance between the center of the lens and the point where the lens focuses light. Lensmaker's Equation formula: 1/f = (n l /n m - 1) * ( 1/r 1 - 1/r 2) where: f: Focal Length, in meter n l: Refractive Index of Lens Material, in meter n m: Refractive Index of Ambient Medium, in meter r 1: Curvature Radius of the First Surface, in meter r 2: Curvature Radius of the Second Surface, in meter This equation holds for all types of thin lenses. Lenses with a negative focal length are said to be diverging because they bend the light rays away from each other. Lensmaker's equation: 1/f = (n 1 /n m-1) * (1/r 1-1/r 2) Where, n 1-Refractive Index of Lens Material n m-Refractive Index of Ambient Medium r 1-Radius of Curvature of the First Surface r 2 - Radius of Curvature of the Second Surface The complete derivation of lens maker formula is described below. Both sides of the lens are convex. When a convex surface faces the object, we say its radius of curvature is positive. and the radius of the back surface of the lens. Lenses with a positive focal length are said to be converging because they bend the light rays toward each other. diverging lens based on the curvature of its faces and the relative indices of the lens material and the surrounding medium. The light rays never actually crossed in this way, but it will appear like they did to the observer in front of the lens. The radii of curvature here are measured according to the Cartesian sign convention.For a double convex lens the radius R 1 is positive since it is measured from the front surface and extends right to the center of curvature. index of refraction of the material surrounding  the lens, radius of lens curvature of the side nearest the "object", radius of lens curvature of the side farthest from the object. In this set up, a positive focal length means that the light rays will be bent by the lens so that they intersect on the right side of the lens. Lensmaker Equation is used to make Lenses. the index of refraction of the medium which forms the environment of the lens, the radius of the front surface of the lens, Example: Calculate the focal length, lens power and lens magnification of a biconvex lens made of crown glass (n = 1.52) in air if … This lensmaker’s equation calculator determines the focal length of a thin lens in air and if this lens is converging or diverging based on known curvature of its surfaces and the refractive index of the lens material. `f = [(n_"lens"/n_"medium" - 1)(1/r_1 - 1/r_2)]^-1`. nm = Refractive Index of Ambient Medium This, of course, isn't what actually happens, but it's a reasonable assumption in certain situations, such as very thin lenses. Generally, we arrange the lens so that the object is on the left side. See Picture 1. The focal length of a lens in air can be calculated from the lensmaker's equation. f = Focal Point nl = Refractive Index of Lens Material Let's use the same indices and magnitudes, but this time the right side of the lens is concave. The radius of curvature can be positive or negative, depending on which way it curves and where it's facing 2. For a thin lens, the power is approximately the sum of the surface powers. For a thin lens, the power is approximately the sum of the surface powers. Using the formula for refraction at a single spherical surface we can say that, For the first surface, For the second surface, Now adding equation (1) and (2), When u = ∞ and v = f. But also, Therefore, we can say that, Where μ is the refractive index of the material. r1 = Radius of Curvature of the First Surface When a concave surface faces the object, we say its radius is negative. See Pictures 1 and 3 ) facing 2 also determines the lens is concave since it extends from! 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