US Patent 11194150 Objective lens for an endoscope and endoscope

An objective lens for an endoscope consists of a negative front group, an aperture stop, and a positive rear group that are arranged in this order from an object side. The front group includes only a negative first lens as a lens. The rear group includes only four lenses that consist of a positive second lens, a positive third lens, a fourth lens, and a fifth lens arranged in this order from the object side, as lenses. The fourth lens and the fifth lens have refractive power having signs different from each other and are cemented to each other. Conditional expression determined in advance about the focal lengths of the second lens and the rear group is satisfied.