What is stray light and how will it affect my system?

Imperfections in the surface of a diffraction grating can cause light to be scattered at an angle different from the diffraction angle. This is typically known as stray light. Stray light (also called ghosts or scattered light) is primarily due to errors in the groove spacing. Since master ruled gratings are fabricated mechanically, they generate more stray light than optically manufactured master holographic gratings. Stray light will interfere with the rest of the light being diffracted correctly off the grating.