The function of a filter in an optical lens

Mar. 04, 2019

Camera lens component by a very important component, is the filter; IR cut filter, that is, the infrared cut-off filter, is placed between the LENS and the Sensor. Since human eyes and CMOS Sensor have different response to each wavelength, human eyes cannot see infrared light, but the Sensor will sense, so IR cut filter is required to block infrared light.

The function of a filter in an optical lens

Ordinary IR will form more serious halo phenomenon:

Ordinary IR adopts reflection type, which has a high transmittance in the visible region and a low reflectivity at the same time, while in the infrared region, it is just the opposite and has a high reflection. Therefore, when the camera takes photos at an Angle, the infrared light will have a large reflection on the IR film. After repeated reflection of the light, the halo phenomenon will be formed on the photo

The blue glass itself is an absorbent glass that absorbs infrared light without much reflection. The copper ion in the glass has the function of absorbing infrared ray, when the camera takes the picture in the Angle, the light passes through the blue glass's main absorption, will not form the halo phenomenon on the picture.

The spectral deviation of ordinary IR with the change of Angle will cause the problem of shading

Common IR center wavelength offset in incident Angle 0 ° to 30 °, 30 nm offset, can form color uneven phenomenon; Blue glass IR center wavelength offset in incident Angle 0 ° to 30 °, offset 2 nm or so, won't appear black Angle and erythema phenomenon.

As the camera of the mobile phone becomes thinner and thinner, the optical design of the lens and the CRA of the sensor are further increased, leading to the above adverse phenomenon of reflective IR becoming more prominent. Blue glass color slant, as well as stray light, ghost problem improved significantly, the photo color more gentle, natural. Therefore, the pursuit of the ultimate effect of the camera must choose blue glass.

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