| 摘要 |
PROBLEM TO BE SOLVED: To provide a lens device capable of bringing an incident angle of a light beam to an interference filter close to 0° using a lens group comprising three lenses.SOLUTION: An infrared lens device is for forming an object image on an image sensor and comprises three lenses, which are, in order from the object side, a first lens which is a positive lens and is convex on the object side, a second lens which is a positive lens and is concave on the object side, and a third lens which is convex on the object side. The second lens has an object-side surface whose maximum tangent angle is 45° to 75°, inclusive, and an image-side surface whose maximum tangent angle is 45° to 75°, inclusive. The third lens has at least one aspherical lens surface, has no inflection point on an object-side surface within an effective diameter thereof, and has a maximum tangent angle of no less than 15°. |
