My physics textbook tells me that when an extended object is placed at the focus of a concave mirror, the light rays reflect and go parallely towards infinity. Same happens when refraction occurs in a convex lens, when the object is placed at the focus of the lens. The book goes on to tell that a real, inverted and highly enlarged image is formed in the given situation.
So my question is :
If the light rays, after getting reflected from a concave mirror (or after getting refracted from a convex lens), go parallely towards infinity, then how do they form a real and inverted image? (Because parallel lines do not intersect).
Because to form real images, actual intersection of light rays must occur. But in this case, that doesn't happen. How can an image, if any, be formed in such a situation?