How will an image producer by a lens changes if half the lens is wrapped in black paper

In every one of the focal points and mirrors, every one of the focuses refract or potentially reflect light to make the picture. So the lower half of the focal point contributes in an indistinguishable sum from done by the upper part. So when you cover half of the focal point with dark paper, you are not giving the refraction a chance to occur from that part, inturn lessening the power/brilliance of the picture. 

An exceptionally basic way you can understand this reality is by taking a gander at yourself in a little and a greater mirror. Under same lighting conditions, you will that in the bigger estimated reflect, the image(your confront) looks brighter.