Derivation of Lensmaker’s formula. Write the basic assumptions used in the derivation of lens – maker’s formula and hence derive this expression. The formula is as follows: $$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$$ Lens Formula Derivation. It is the lens maker's formula where lens is the convex lens in this case. Thus, 1 f = (n −1) 1 R1 + 1 R2 , (9) which is the lensmaker’s formula. 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. It is so called because it is used by lens manufacturers to make lenses of particular power from the glass of given refractive index. Derive the formula where s = distance of object from lens s' = distance of image from lens f = focal length of the lens. 1 See answer jameyj344 is waiting for your help. Derivation. Add your answer and earn points. These lenses have negligible thickness. Consider a convex lens with an optical center O. For a thin lens, the power is approximately the sum of the surface powers.. Let F be the principle focus and f be the focal length. Lens makers formula: It is a relation between the focal length of a lens to the refractive index of its material and the radii of curvature of its two surfaces. Lence is a non-existent word.-6 ; Figure (a) Figure (b) Figure (c) The above figure shows the image formation by a convex lens. Lens-Maker's Formula. Lens formula is applicable for convex as well as concave lenses. Writing the lens equation in terms of the object and image distances, 1 o + 1 i = 1 f. (8) But o1 and i2 are the object and image distances of the whole lens, so o1 = o and i2 = i. We have taken the convex lens to prove this formula and make sure that these are very thin lenses. The radius R 2 is negative since it extends left from the second surface.