Optical system and optical camera working at far-infrared waveband

An optical system working at a far-infrared waveband, comprising three optical elements, the three optical elements being, along the optical axis in order from an object side to an image side:

• a first sulfur refractive lens, a metalens and a second sulfur refractive lens;
• the first sulfur refractive lens and the second sulfur refractive lens have positive refractive power;
• each of three optical elements comprising an object-side surface facing towards the object side and an image-side surface facing towards the image side;
• the metalens comprises a substrate and a plurality of unit cells, and a plurality of nanostructures are set in the unit cells;
• the optical system satisfies the following condition with a unit of 1/mm:
• 0.25
• ≤
• n
• *
• (
• ❘
• "\[LeftBracketingBar]"
• C
• 1
• ❘
• "\[RightBracketingBar]"
• +
• ❘
• "\[LeftBracketingBar]"
• C
• 2
• ❘
• "\[RightBracketingBar]"
• )
• ≤
• 2
• .
• 0
• ⁢
• 1
• wherein when n is a refractive index of the first sulfur refractive lens, C1 is a curvature of the object-side surface of the first refractive lens, C2 is a curvature of the image-side surface of the first refractive lens;
• when n is a refractive index of the second sulfur refractive lens, C1 is a curvature of the object-side surface of the second refractive lens, C2 is a curvature of the image-side surface of the second refractive lens.