Which optical effects did Leonardo da Vinci explain in his notes on painting?

In his notebooks, Leonardo da Vinci identified 10 optical functions of the eye—darkness, light, body and color, shape and location, distance and closeness, and motion and rest—as essential components of painting. To master these, he explored various perspectival systems, including linear and aerial perspective, as well as concepts like wide-angle vision and lateral recession.1

Leonardo provided detailed guidance on how to depict specific optical effects, including:

• Light and Shadow: He analyzed the modulation of light and shade to create depth and form.1
• Atmospheric Effects: He utilized atmospheric perspective, which involves the blurring of clarity and the progressive lightening of tones to simulate the impact of the atmosphere on distant objects.12
• Nature and Environment: He offered techniques for rendering distance, smoke, water, and the softening of edges.1
• Human Form: He documented methods for portraying human anatomy, proportions, and facial expressions.1

Furthermore, Leonardo famously employed sfumato—a technique of blending tones to eliminate harsh outlines—to mimic the way forms appear to evaporate into the surrounding air.3