When there is a strong light source in the environment (such as the sun or high-power lamps), the light from the source reflects upon reaching the lens. This reflection can then reach different parts of the lens, aperture, or sensor, causing unintended patterns like glare or starbursts in the image. This phenomenon, which degrades image quality, is known as "flare" or "glare."

In fact, stray light is described using various terms across different industries, including "stray light," "lens flare," "veiling glare," "ghosting image (flare)," and others. Most of these terms lack strict definitions.

Causes of Flare

There are many variables that contribute to flare, stemming from both natural environmental factors and camera hardware components:

1. Environmental Factors: These include everything between the object and the camera lens, such as:

   • Haze or dust particles in the air
   • Reflections between optical components and dust or dirt on the lens

2. Camera System Hardware: Flare can also originate from components such as:

   • Edge reflections from lenses, shutters, or the camera body itself
   • Optical system effects like spherical aberration, chromatic aberration, and light leakage

Flare occurs when light reflects within the lens system, causing unwanted artifacts in the image.