An optical system (e.g., a telescope) comprising an optical assembly that reflects and refracts light rays through a single window about an optical path to a detector. A field-of-view bypass assembly comprises a bypass mirror movably coupled with respect to the optical assembly. The bypass mirror is selectively translatable and tiltable between a bypass configuration and a retracted configuration. In the bypass configuration, the bypass mirror is disposed in and interrupts the primary optical path and oriented to define a secondary optical path to the detector. In the retracted configuration, the bypass mirror is both disposed out of the primary optical path and is properly shielded to prevent stray light reflections.