A Quick Learning Algorithm Inspired by Human Rule Discovery

An objective optical system for endoscopes consisting, in the order from the object side, of a front lens unit having negative refractive power, an aperture stop and a rear lens unit having positive refractive power and comprising at least one aspherical surface in each of the lens units. This objective optical system for endoscopes has distortion of a small absolute value, a distortion curve of natural shape, favorably corrected aberrations, and is composed of lens elements easily manufacturable.