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