What Causes a Lens Flare?

What Causes a Lens Flare?

Unlike your eye, which has only one very flexible
lens, camera lenses are typically made up of a series
of inflexible lens elements. These elements are
coated to prevent light reflecting off of them under
normal circumstances. Extreme amounts of light,
however, are reflected somewhat by each element.
Zoom lenses contain many focusing elements and
tend to generate a complex-looking flare with lots
of individual reflections. Prime lenses generate
fewer.
Many factors besides the lens elements contribute
to the look of a flare. Aperture blades within the
lens cause reflective corners that often result in
streaks; the number of streaks corresponds to
the number of blades. The shape of the flares
sometimes corresponds to the shape of the aperture
(a pentagon for a five-sided aperture, a hexagon for
six). Dust and scratches on the lens also reflect light.
FInally, lens flares look very different depending
on whether they were shot on film or video; excess
light bleeds out in different directions and patterns.