Patent ID: 8345357

Claim:
An optical system which is used in a wavelength range including a near ultraviolet light range having a wavelength longer than approximately 350 nm and a visible light range, comprising: at least two first positive lenses satisfying the following conditional expressions (1) to (3) disposed closer to a contraction side than an aperture stop; and at least one second positive lens satisfying the following conditional expressions (1), (4) and (5): 60<Vd (1) 0.67<0.0018 Vd+P (2) −7.5×10 −6 <dN/dT<− 0.5×10 −6 (3) 0.645<0.0018 Vd+P (4) 9×10 −6 <dN/dT (5) where, Vd denotes an Abbe number at the d-line, P=(Ng−NF)/(NF−NC), Ng denotes a refractive index at the g-line, NF denotes a refractive index at the F-line, NC denotes a refractive index at the C-line, and dN/dT denotes a rate of change of the refractive index with respect to temperature in a vicinity of room temperature.