Patent ID: 11927781
Assignee: BAE SYSTEMS PLC
Field: Optics (Instruments)
Classification: CPC G  F | IPC G

Claim 0:
1. An optical device comprising:
an objective lens defining a focal plane and an eyepiece spaced apart therefrom, defining an optical axis therethrough;
an optical member having a planar face, arranged on the optical axis proximal the focal plane and between the objective lens and the eyepiece, wherein the planar face is arranged to oppose the objective lens; and
a filter assembly comprising a notch filter arranged to attenuate transmission of electromagnetic radiation having a first wavelength incident thereupon, wherein the notch filter is arranged in front of the optical member; and
wherein the notch filter is arranged between the optical member and the objective lens, and at an oblique angle to the optical axis;
whereby, in use, incident electromagnetic radiation having a predetermined wavelength propagating along the optical axis is reflected by the notch filter away therefrom, wherein the first wavelength and the predetermined wavelength are different.