IR Cut filter , that is, the infrared cut-off filter,it is placed between Sensor and CCTV LENS.Because human eyes and cmos sensor have Responses for different wavelengths light.infrared light is invisible for human eyes. But it is visible for the cmos sensor.So we need the ir cut filter to block the infrared light.
IR Cut filter is divided into reflective (ordinary IR) and absorption type (blue glass).The following figure can be seen the difference of the two type ir cut filter in different light.
Below is the contrast characteristics of ordinary IR cut filter and blue glass.blue glass is about 10 times expensive than ordinary IR.But it has its own advantages.reflected in 2 aspects
One :ordinary IR cut filter will a serious halo phenomenon.
ordinary IR cut filter effect below
Ordinary IR cut filter uses the reflection type, in the visible light region has the high transmittance, at the same time, has the low reflectivity, but in the infrared region is opposite, the reflection is higher. So, when the camera angle pictures will have greater infrared reflection in the IR film, after repeatedly reflected light, will form a halo in the photo.
Blue glass ir cut filter effect below
Blue glass itself is a kind of absorption of glass, there is absorption of infrared light, there is no great reflection. The copper ions in glass with infrared absorption function, when the camera angle in the photograph, light through the main absorption blue glass, not forming a halo phenomenon in the photo
Two: ordinary IR with the angle of the changes led to spectral shift, will lead to the problem of shading
The ordinary IR center wavelength offset when the incident angle is 0 degrees ~30, offset 30nm, will form the color uneven; the blue glass IR wavelength offset when the incident angle is 0 degrees ~30, offset 2nm, does not appear Noire and erythema phenomenon
Now more and more m5 m6 lens use the blue glass ir cut filter.
Junyi Zhao