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

Claim 15:
16. 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, 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 arranged between the optical member and the objective lens;
wherein the notch filter is arranged at an oblique angle to the optical axis, and to attenuate electromagnetic radiation having a wavelength range including the first wavelength, wherein the wavelength range is at most 30 nm, wherein the oblique angle is in a range from 5° to 85°;
wherein 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;
wherein the predetermined wavelength is in a range from 100 nm to 1100 nm; and
wherein a difference between the predetermined wavelength and the first wavelength is in a range from 0.1 nm to 150 nm.