Patent ID: 6268969
Filing Date: 2001-07-31
Classification: G02B

Abstract:
An optical system comprising, in order from an object side to an image side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, said second lens unit being moved during focusing, wherein said first lens unit has a diffractive portion having a positive refractive power and a first lens subunit of a positive refractive power, and said first lens subunit comprises at least one positive lens and at least one negative lens, said optical system satisfying the following conditions:0.005<.phi..sub.D /.phi..sub.1a <0.0550<.nu..sub.1ap <7525<.nu..sub.1an <60where.phi..sub.D is a refractive power of an optical element having said diffractive portion having a positive refractive power in said first lens unit,.phi..sub.1a is a refractive power of said first lens subunit,.nu..sub.1ap is an Abbe number of a material of the positive lens included in said first lens subunit when there is only one positive lens in said first lens subunit, or a mean value of Abbe numbers of materials of positive lenses included in said first lens subunit when there is more than one positive lens in said first lens subunit, and.nu..sub.1an is an Abbe number of a material of the negative lens included in said first lens subunit when there is only one negative lens in said first lens subunit, or a mean value of Abbe numbers of materials of negative lenses included in said first lens subunit when there is more than one negative lens in said first lens subunit.