A convex lens is a lens formed by two spherical surfaces bulging outward. It converges a beam of light incident on it and hence is known as a converging lens. The nature, position, and size of the image formed depend on the position of an object. It can be studied by keeping the object, the lens, and the image all on the same straight line and observing the image for different object distances. A convex lens can form real and virtual images. Real images are inverted while virtual images are erect. Based on the position of the object, the image formed can be diminished, enlarged, or of the same size.
In this video the nature, position, and size of the image formed by a convex lens is studied for different positions of a lighted candle (object)