Patent ID: 8184388
Filing Date: 2012-05-22
Classification: G02B

Abstract:
1. An image forming optical system comprising: at least one cemented lens, wherein the cemented lens includes a first lens element e the first lens element e the first lens element e a combined refracting power of the second lens element e the cemented lens satisfies the following conditional expression (1) where, Neff denotes an effective refractive index when the cemented lens is assumed to be one lens, and is expressed by the following expression and ν eff is an effective Abbe's number when the cemented lens is assumed to be one lens, and is expressed by the following expression where, P denotes Petzval's sum, F n f ν wherein the lens unit having at least the one cemented lens includes at least one positive lens et apart from the cemented lens, and the image forming optical system satisfies the following conditional expressions (2) and (3-2) where, Ndet and ν det denote a refractive index and Abbe's number respectively of the positive lens et.