To make a further explanation on some questions about optical imaging using a light field camera

In traditional optics, the focusing should be done before the exposuring. However, a light field camera makes it a reality to take a photograph before the focusing. The principle of a light field camera consists of some fundamental theories on optical imaging, including pinhole imaging, depth of focus, digital refocusing, synthetic aperture imaging, etc. It is easier for students to understand the above theories through learning the theory and experiment of a light field camera. Meanwhile it also involves some optical knowledge for a light field camera during the acquisition and processing images. In the paper, we will discuss the similarities and differences on optical properties among the pinhole, the convex lens and the light field camera. Our intention is to make these optical theories much easier to understand for students in our teaching work.