Stray light can be characterized in two distinct types: ghosts and flare or veiling glare.
Ghosts occur in imaging systems when light from a source in the image field undergoes two or more unwanted reflections and then falls on the imaging device, creating an unwanted ghost image. For digital cameras, one of the most common sources of ghost images is light that reflects off the imaging device back into the optical system and then reflects off a lens surface back to form a secondary image.
Flare, or veiling glare, generally occurs when light scatters inside the optical system either off imperfections in the optical surfaces, or off mechanical elements in the system. Veiling glare can also be caused by atmospheric reflection of light such as with haze or sky glow.
- Typically caused by unintended reflections between imaging surfaces
- Higher or unblocked diffractive orders from gratings
- Secondary imaging of bright scattering surfaces
- Flare or veiling glare
- Light incident on the image from outside of the optical system’s field
- Bright sources within the field of view, thermal radiation emanating from warm surfaces
- Often the result of light scattering within the optical system