An optical system with a tilted window. The novel optical system includes a first optical element for receiving an input signal and generating an output signal; a first window adapted to transmit the output signal, the first window being tilted at an angle relative to an axis normal to an optical axis of the system; and a second window adapted to compensate for the first window. In an illustrative embodiment, the first window is an input window of a camera adapted to detect the output signal and is tilted such that reflections from and within the window do not strike detector elements of the camera. In a preferred embodiment, the second window has similar thickness and optical properties as the first window, and is positioned in the optical path of the input signal, tilted at an angle designed to compensate for the first window.