What do you mean by ghosts?

In the imaging optical system, one or more images similar to the image point exist near the image point except the image point.

Other image points are collectively referred to as "ghost points". For example, the optical theory of glasses thinks that the refractive power of glasses can make the observed object form a clear image at the far point of the wearer, and it can also be explained that the light of the observed object is deflected through the lens and concentrated on the retina to form an image point. However, due to the different curvatures of the front and rear surfaces of the refractive lens and the existence of a certain amount of reflected light, internal reflected light will be generated between them. The internal reflected light will produce a virtual image near the apogee sphere, that is, the virtual image point near the retinal image point. These virtual image points are the ghosts seen by the eyes. Reducing the reflective film can avoid the existence of "ghost". It usually appears in photos, especially when shooting against the light. We call this phenomenon of photo whitening and halo caused by strong light "flare". When sunlight or a point light source enters the lens, after many reflections, a clear bright spot is formed at the relative position of the light source, just like a ghost, which is called a ghost. A ghost is a kind of light.