Simplify the following text for a Grade 6 native English-speaking person.
Original: If a camera lens were to be constructed from a single lens of 500 mm focal length , then when the lens is focused on an object at infinity , the lens will be 500 mm away from the focal plane where the film or sensor is . The center of the lens is referred to as the optical center of the lens .
Simplified: The less specific use is to mean a lens that has a longer focal length than a normal lens .