Patent ID: 7426083

Claim:
An imaging optical system comprising: a first lens unit having positive refractive power, the first lens unit including a first lens sub-unit comprising a single lens having a positive refractive power, a second lens sub-unit including a diffractive optical part and having a positive refractive power, and a third lens sub-unit having a negative refractive power, the first to third sub-units being disposed in this order from an object side to an image side; and a second lens unit having a negative refractive power, the first lens unit and the second lens unit being disposed in this order from the object side to the image side; wherein the diffractive optical part is convex towards the object and the following condition is satisfied: 0.05 <L 1 /OTL <0.2 where L 1 denotes a distance between the first lens sub-unit and the second lens sub-unit and OTL denotes the total optical length of the imaging optical system to the imaging plane.