Patent ID: 6943959

Claim:
An objective optical system which is provided with, in a nearer order from its object, a first lens group which has a negative refractive power, a brightness diaphragm, and a second lens group which has a positive refractive power, and a moving lens group which moves on an optical axis; wherein conditions 2≦D L /f W ≦6, and −2≦D VH /f W ≦0.37 are satisfied under condition that D L (mm) indicates an air-converged length from an end surface near an image in the first lens group to an end surface nearer to an object in the moving lens group, f W (mm) indicates a focal length in an entire system in a wide angle end, D VH (mm) indicates a distance from the end surface near the object in the moving lens group to a front principal point.