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

Claim 14:
15. A method comprising:
arranging (i) an objective lens that defines a focal plane and (ii) an eyepiece spaced apart from the objective lens, wherein the objective lens and/or the eyepiece defines an optical axis;
arranging an optical member having a planar face between the objective lens and the eyepiece, wherein the planar face is arranged to oppose the objective lens;
arranging a filter assembly comprising a notch filter to attenuate transmission of electromagnetic radiation having a first wavelength incident thereupon, the notch filter is arranged in front of the optical member, wherein the notch filter is arranged between the optical member and the objective lens, and at an oblique angle to the optical axis; and
reflecting, by the notch filter, incident electromagnetic radiation having a predetermined wavelength propagating along the optical axis away therefrom, wherein the first wavelength and the predetermined wavelength are different.