BAE Systems PLC
OPTICAL DEVICE

Abstract:

An optical device 10 comprises an objective lens 11 defining a focal plane FP and an eyepiece 12 spaced apart therefrom, defining an optical axis OA therethrough. The optical device 10 comprises an optical member 13 having a first planar face 14, arranged on the optical axis OA proximal the focal plane FP, wherein the first planar face 14 is arranged to oppose the objective lens 11. The optical device 10 comprises a filter assembly 100 comprising a first notch filter 101 arranged to attenuate transmission of electromagnetic radiation having a first wavelength .lamda..sub.1, wherein the first notch filter 101 is arranged in front of the optical member 13. The first notch filter 101 is arranged at a first oblique angle .theta..sub.1 to the optical axis OA whereby, in use, incident electromagnetic radiation having a predetermined wavelength .lamda..sub.i propagating along the optical axis is reflected by the first notch filter 101 away therefrom, wherein the first wavelength .lamda..sub.1 and the predetermined wavelength .lamda..sub.i are different. In this way, retro-reflection of the incident electromagnetic radiation towards a source thereof is reduced, thereby better detection of the optical device 10.