The instrument is called a darkroom. It is a wooden cuboit box which has on the one side converging lens (which collect the light rays from each point of the object) which can be easily moved in order to adjust the distance from the opposite side of the box and to control the focus of the image. Just at the opposite side of the box there is a translucent glass, so that the image of each object can be displayed (inverted) on the translucent glass because of the straight direction of light. We are able to observe that the relative sizes of the object and its image are proportional to their respective distances from the lens of the darkroom. Approaching the object, for instance, closer to the lens of the darkroom, the greater the size of its image is getting, and vice versa.