What does double exposure mean?

The so-called second exposure is to make two exposures when shooting. For the second exposure, you must first determine the shooting location and object with the support of a tripod, and then make the first exposure after framing and composition. The exposure is slightly less than the accurate exposure, preferably one-third of the insufficient and correct exposure, which can reflect the outline of the shadow.

It is necessary to keep the camera and framing composition still, and then make a second exposure after dark. This exposure requires measuring light. In order to enhance the lighting effect, the exposure of one step can be appropriately increased. The photos taken in this way can make two objects equally eye-catching.