A convex lens forms a virtual and erect image when the object is placed between the optical
centre (O) and focus (F′).
Consider two rays starting from the top of the object. The ray (AP) going parallel to the principal axis after refraction passes through the focus (F). The ray (AO) passing through the optical centre passes through the lens undeviated. These refracted rays produced backwards as shown by dotted lines. They meet at A′. Draw perpendicular A′B′ on the principal axis. Thus A′B′ is the complete image of object AB.
