SUMMARY
Each uncoated air-to-glass surface reflects about 4% of light. Professional zoom lenses, like the 24-70mm f/2.8, can have around 30 such surfaces, significantly reducing light transmission without coatings. Flare occurs when reflected light lands on the sensor, often appearing as ghost images or a general loss of contrast known as veiling glare. These artifacts can be shaped by the lens aperture and are also influenced by reflections from the camera's sensor itself.
TAKEAWAYS
Uncoated lens surfaces reflect approximately 4% of light.
Modern lenses have many elements, increasing potential for light reflection and flare.
Flare and veiling glare reduce image contrast and can create ghosting artifacts.
Sensor reflections can also contribute to ghosting, especially in mirrorless systems.