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, conditions such as 2≦DL/fW≦6, and −2≦DVH/fW≦0.37 are satisfied...http://www.google.ca/patents/US6943959?utm_source=gb-gplus-sharePatent US6943959 - Objective optical system
