Such people can see only distant objects clearly. Glasses with convex lenses are used to correct farsightedness. A magnifying glass is a double convex lens that behaves like two prisms connected together at their bases. It can concentrate light rays from the sun to such a degree that they can bum a hole in paper or cause a fire. A convex lens has a focal point.
Light coming from that point is refracted by the lens to become parallel or vice versa.
An object that is beyond the focal point of a lens will be focused upside-down on the other side of the lens. Both a camera and the eye have a convex lens which focuses the image upside-down on its detector. The camera uses film to detect the image, while the eye has its retina to detect the image. If a person's eyeball is too long from front to back, the point of focus will be in front of the retina and the person will be nearsighted. Such people can see only close objects clearly.