The camera lens assembly consists of a very important component, the filter; IR cut filter, the IR cut filter, placed between LENS and Sensor. Because the human eye and the CMOS Sensor respond differently to each wavelength, the human eye can’t see the infrared light but the sensor can sense it, so the IR cut filter is needed to block the infrared light.
The IR cut filter is classified into a reflective type (normal IR) and an absorption type (blue glass). The following picture shows the difference between the two in different light:
The following is a comparison of the characteristics of ordinary IR and blue glass. Blue glass is about 10 times more expensive than ordinary IR. It has its advantages, which are reflected in two aspects:
A: Ordinary IR will form a more serious halo phenomenon:
Here is the general IR effect:
Ordinary IR adopts a reflection type, and has a higher transmittance in the visible light region, and a lower reflectance, and in the infrared region, the reflection is higher. Therefore, when the camera is taking photos at an angle, the infrared light will have a large reflection on the IR film. After multiple reflections by the light, a halo phenomenon will form on the photo.
Here is the effect of blue glass:
Blue glass itself is an absorbing glass that absorbs infrared light without significant reflection. The copper ions in the glass have the function of absorbing infrared rays. When the camera takes a photo at an angle, the light is mainly absorbed by the blue glass, and no halo phenomenon is formed on the photo.
B: The normal IR changes with the angle causes the spectral shift, which causes the problem of shading:
The wavelength shift of the ordinary IR center is 0°~30°, and the offset is about 30nm, which will cause color unevenness. The wavelength shift of the blue glass IR center is 0°~30° at the incident angle, and the offset is about 2nm. There are no black spots and erythema.
to sum up:
The mobile phone camera is getting thinner and thinner, and the optical design of the lens and the CRA of the sensor are further increased, resulting in the above-mentioned undesirable phenomenon of the reflective IR being more prominent. The blue glass has improved color deviation, stray light and ghosting problems, and the photos taken are softer and more natural. Therefore, the camera that pursues the ultimate effect must choose blue glass.
Click the below picture to know more our IR USB camera module