Convex Lens u = Distance of object from the optical center of the lens. Lens formula is applicable for convex as well as concave lenses. For latest information , … f = focal length of the lens. Applicable for both the convex and concave lenses, the lens formula is given as: 1/v - 1/u = 1/f Where, v = Distance of image formed from the optical center of the lens. THIN LENS FORMULA : FOR CONCAVE LENS. Let a concave lens have two spherical surfaces X 1 P 1 Y 1 and X 2 P 2 Y 2 having radius of curvature as R 1 and R 2 respectively. Lens Formula Derivation. In this video, we are going to derive the lens formula using the properties of the triangle. The formula is as follows: $$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$$ Lens Formula Derivation. Consider an object placed in front of a concave lens of focal length "f " on the principle axis of the lens. Concave lens forms a virtual and erect image at a distance of " q " from the optical centre of the lens as shown in the diagram below. (viii) represents Lens maker formula. Consider a convex lens with an optical center O. These lenses have negligible thickness. The formula formed will be a general formula. STEP I. Refraction at X 1 P 1 Y 1. This lens formula is applicable to both the concave and convex lens. For aconcave lens, the lens equation is the same but the value of fis nownegative. If this equation shows a negative focal length, then the lens is a diverging lens rather than the converging lens. Let F be the principle focus and f be the focal length. If the equation shows a negative image distance, then the image is a virtual image on the same side of the lens as the object. Ray diagrams for such lenses are drawn using: a ray from the top of the object through the middle of the lens; Eqn. Derivation of Lens Maker Formula for a Concave Lens. Section 3: Concave Lenses 12 3. Concave Lenses Concave lenses always produce upright, virtual images.