Why is there a lavender film on the surface of camera lens?

This is called antireflection coating. Used to increase light transmittance.

When light enters another medium from one medium, it will lose some energy when reflected on the interface. For example, when the light reaches the lens during photography, each piece of glass in the lens has two interfaces with the air and will be reflected twice. There are more lenses in the lens, and the reflected light will be considerable.

Anti-reflection film is a transparent material coated on glass. It seems that there are two more reflections (there are two interfaces between air, antireflection film and glass), and antireflection film only uses the reflection of light and superimposed interference.

Its thickness is 0.4 wavelength of 65438+ light wave, which makes the reflected light wave passing through the two interfaces differ by 0.5 wavelength. After the two waves are superimposed and interfered, you will find that they cancel each other out!

It can be said that it redistributes the energy in the process of light refraction and reflection, strengthens the refracted light energy and reduces the reflected light energy.

Of course, there are many wavelengths of visible light, and the antireflection film on the lens can only be used for one wavelength of light, generally green light (the human eye is most sensitive to green light), so the green component in the reflected light is reduced a lot, which is why it appears lavender.