It's fabricated by special blue glass (BG39 from Schott or equivalent). The glass will absorb IR wavelength and let visible light pass. It widely used for digital camara.
Item
Specifications
Material
Schott D263T or BG39 and etc.
Dimension X×Y(φ)
1×1mm~25.4×25.4mm；φ3~φ25.4mm
Dimension tolerance
±0.05mm
Parallelism
＜10 seconds
Clear Aperture
85%
Surface Quality
MIL40-20
Flatness(per 10mm)
λ/8@632.8nm
Coating
ARCoating@400~630nm;
HR Coating @700~1100nm