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