A lens system for a camera objective has a plurality of optical lenses that are arranged one after another along an optical axis and are configured for imaging in the visually perceivable spectral range. At least a part of the optical lenses has two types of lens faces that intersect a beam path of the camera objective. At least three of said lens faces are provided with a first anti-reflective coating which has a larger reflectance in at least one partial region of the visible spectral range than a second anti-reflective coating of the remaining lens faces. In addition, a camera objective including the lens system and a method for producing a lens system are provided.

A display device according to one or more embodiments may include a lightguide plate comprising a transparent part, and an incident surface, the lightguide plate configured to display at least one pattern; and a light source facing the incident surface. The lightguide plate may include a plurality of prisms on a surface of the lightguide plate, the plurality of prisms being arranged along the at least one pattern to reflect light emitted from the light source and entering the lightguide plate through the incident surface out of the lightguide plate through an emission surface of the lightguide plate, and a transparent protective layer covering at least a part of the emission surface, the protective layer having a smaller refractive index than the lightguide plate.

A display device according to one or more embodiments may include a lightguide plate comprising a transparent part, and an incident surface, the lightguide plate configured to display at least one pattern; and a light source facing the incident surface. The lightguide plate may include a plurality of prisms on a surface of the lightguide plate, the plurality of prisms being arranged along the at least one pattern to reflect light emitted from the light source and entering the lightguide plate through the incident surface out of the lightguide plate through an emission surface of the lightguide plate, and a transparent protective layer covering at least a part of the emission surface, the protective layer having a smaller refractive index than the lightguide plate.

A lens system for a camera objective has a plurality of optical lenses that are arranged one after another along an optical axis and are configured for imaging in the visually perceivable spectral range. At least a part of the optical lenses has two types of lens faces that intersect a beam path of the camera objective. At least three of said lens faces are provided with a first anti-reflective coating which has a larger reflectance in at least one partial region of the visible spectral range than a second anti-reflective coating of the remaining lens faces. In addition, a camera objective including the lens system and a method for producing a lens system are provided.

The present invention relates to a method for detecting a mark that is invisible in the visible light region. Here, the invisible mark is displayed on a card using a characteristic according to which the color of light is changed by means of a refractive index difference according to media in the visible light region. According to the method for detecting the invisible mark, it may be quickly determined whether the card is a counterfeit card in an investigation. In addition, since it is unnecessary to repeatedly inspect the card to be checked using various wavelengths, the time required for determining whether the card is a counterfeit card may be reduced.