What is the purpose of a lens cap on optical devices?

The purpose of a lens cap on optical devices is primarily to protect the lens from dust, scratches, and moisture. Keeping the lens covered when not in use prevents these elements from damaging the glass surface, which can significantly impact the clarity and quality of the images produced. Dust and scratches can lead to unwanted artifacts in photographs or obstruct the view through the device, while moisture can cause fogging or even mold growth, compromising the lens's integrity over time. Therefore, using a lens cap serves as a simple yet effective measure to maintain the lens in optimal condition, ensuring clear and sharp imaging when the optical device is employed.