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Note however that in areas of optics other than design, other sign conventions are sometimes used. In particular, many undergraduate physics textbooks use the Gaussian sign convention in which convex surfaces of lenses are always positive. [3] Care should be taken when using formulas taken from different sources.
There are other sign conventions such as Cartesian sign convention where the thin lens equation is written as + =. For a thick lens, the same form of lens equation is applicable with the modification that parameters in the equation are with respect to principal planes of the lens.
This Newtonian form of the lens equation can be derived by using a similarity between triangles P 1 P O1 F 1 and L 3 L 2 F 1 and another similarity between triangles L 1 L 2 F 2 and P 2 P 02 F 2 in the right figure. The similarities give the following equations and combining these results gives the Newtonian form of the lens equation.
For a diverging lens (for example a concave lens), the focal length is negative and is the distance to the point from which a collimated beam appears to be diverging after passing through the lens. When a lens is used to form an image of some object, the distance from the object to the lens u, the distance from the lens to the image v, and the ...
Curvature radius of lens/mirror r, R: m [L] Focal length f: m [L] Quantity (common name/s) (Common) symbol/s Defining equation SI units Dimension Lens power P
where S 1 is the distance from the object to the lens, θ 2 is the distance from the lens to the image, and f is the focal length of the lens. In the sign convention used here, the object and image distances are positive if the object and image are on opposite sides of the lens. [45]
For a single lens surrounded by a medium of refractive index n = 1, the locations of the principal points H and H ′ with respect to the respective lens vertices are given by the formulas = ′ = (), where f is the focal length of the lens, d is its thickness, and r 1 and r 2 are the radii of curvature of its surfaces. Positive signs indicate ...
The coefficients r and t are generally different between the s and p polarizations, and even at normal incidence (where the designations s and p do not even apply!) the sign of r is reversed depending on whether the wave is considered to be s or p polarized, an artifact of the adopted sign convention (see graph for an air-glass interface at 0 ...