The role of the filter in the optical lens

The camera lens assembly consists of a very important component, the filter; IR cut filter, the infrared cut filter, which is placed between the LENS and the Sensor. Because human eyes and CMOS Sensor respond differently to each wavelength, infrared light is not visible to the human eye but sensor will sense it. Therefore IR cut filter is required to block infrared light.

IR cut filter is classified into two types: reflective type (common IR) and absorption type (blue glass). The following figure shows the difference between the two under different lighting conditions:

The following describes the characteristics of ordinary IR and blue glass. Blue glass is about 10 times more expensive than ordinary IR. It has its advantages. It is reflected in two aspects:

One: Common IR will form a more serious halo phenomenon:

The

Common IR uses a reflective type, which has a relatively low reflectivity in the visible light region and a relatively low reflectivity in the infrared region. Therefore, when the camera takes pictures at an angle, infrared light will have a large reflection on the IR film, and after multiple reflections of light, it will form a halo phenomenon on the photo.

Blue glass itself is an absorbing glass that absorbs infrared light and does not reflect much. The copper ions in the glass absorb infrared light. When the camera takes pictures at an angle, the absorption of light through the blue glass will not cause halos on the photo.

Second: Normal IR causes spectral shifts due to angle changes, which can lead to shading problems:

The common IR center wavelength offset at the incident angle of 0°~30°, offset by about 30nm, will cause color non-uniformity; the blue glass IR center wavelength offset at the incident angle of 0°~30°, offset by 2nm, There will be no black corners and erythema.

to sum up:

As the camera of the mobile phone becomes thinner and thinner, the optical design of the lens and the CRA of the sensor further increase, resulting in the above-mentioned unfavorable phenomena of the reflective IR becoming more prominent. The blue glass significantly improved the color cast, stray light, ghosting, and the colors of the photos were softer and natural. Therefore, the blue camera must be selected for the camera with the utmost effect.

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