What is the second exposure in photography?

Secondary exposure is a unique imaging method in the film era. For example, if you want to take a picture of the sea with the moon in the morning, you must make a second exposure. Take a picture of Zhang Yueliang first, and then take a picture of the sea on the negative of the moon. This is a second exposure.

Now is the digital age, and there is no such imaging method as film. Only when the software processes the synthesized image can it have an effect similar to that of the previous film secondary exposure.

Nowadays, photoshop is widely used, which is convenient, practical and easier to realize.

Supplement: Nikon series SLR has double exposure function, that is, the machine itself has software or algorithm to synthesize images, without going through the PS of the computer. Canon's machine does not have this function.