🔎 Lens Ray Diagram (Convex & Concave)

📖 The Physics

A convex (converging) lens bends parallel rays of light together to a single focus; a concave (diverging) lens spreads them apart. That one difference explains cameras, glasses and magnifiers.

To find an image, trace two easy rays: one parallel ray (which leaves the lens through the focus) and one straight through the centre (undeviated). Where they meet — or appear to meet — is the image.

With a convex lens, sweep the object in: beyond 2F → small real image; at 2F → same size; between F and 2F → magnified real; at F → image at infinity; inside F → magnified virtual (a magnifying glass). A concave lens always gives a small upright virtual image (like a peephole).