How to Select Filter in Machine Vision

The camera lens assembly consists of a very important component, that is, a filter; IR cut filter, namely, the infrared cut-off filter, is placed between LENS and Sensor. Because the human eye and CMOS sensor have different responses to different wavelengths, the human eye cannot see infrared light but the sensor will sense it, so IR cut filter is required to block infrared light.

IR cut filter

IR cut filters are divided into reflective (ordinary IR) and absorptive (blue glass) types. The following figure shows the difference between the two in different light:

The characteristics of ordinary IR and blue glass are compared as follows. Blue glass is about 10 times more expensive than ordinary IR and has its own advantages, which are reflected in two aspects:

1: Ordinary IR will form a serious halo phenomenon:

The following are common IR effects:

Ordinary IR adopts reflective type, which has a high transmittance in the visible light area and a low reflectance at the same time, while in the infrared area, on the contrary, the reflectance is high. Therefore, when the camera takes a picture at an angle, the infrared light will have a large reflection on the IR film. After multiple reflections of the light, a halo phenomenon will be formed on the picture

The following is the effect of blue glass:

Blue glass itself is an absorbing glass, which can absorb infrared light and does not reflect much. The copper ion in the glass has the function of absorbing infrared rays. When the camera takes a picture at an angle, the light will pass through the main absorption of blue glass and will not form a halo on the picture.

2: The spectral shift of ordinary IR with the change of angle will lead to the problem of shading:

The shift of the central wavelength of ordinary IR at the incidence angle of 0 °~30 ° and the shift of about 30nm will result in uneven color; The shift of IR central wavelength of blue glass is about 2nm at the incidence angle of 0 °~30 °, and there will be no black corner and erythema.

Summary:
The mobile phone camera is getting thinner and thinner, the optical design of the lens and the CRA of the sensor are further increased, resulting in the above undesirable phenomenon of reflective IR. Blue glass has significantly improved the color deviation, stray light and ghost, and the color of the photos taken is more soft and natural. Therefore, blue glass is a must for cameras that pursue the ultimate effect.

ABOUT BORISUN

Hanzhong Brisun Optics Co., Ltd. Is the high precision optical element manufacturer provides customized production of Various optical lenses, including spherical lens, cylindrical lens, optical window, mirror, prism, filter, metal base mirror and other high-precision optical elements. The base materials include various optical glass, fused quartz, calcium fluoride (CaF2), zinc selenide (ZnSe), germanium (GE), silicon (SI), sapphire, metal and other materials. And provide antireflective film, high reflection film, spectroscopic film, metal film and other optical coatings.

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