Introduction to lens development

Lens washing: spots caused by multiple reflections of light in the lens. It goes without saying that photography needs sunshine and cannot do without it. But sometimes, the sun will also destroy photography and bring disaster to photos that were originally thought to be very satisfactory. That's true. That is, once the sun shines directly on the lens of the camera lens, and you don't notice it, you press the shutter, and this photo is basically invalid, and it is difficult to enlarge it.