Patent ID: 11971607
Assignee: CANON KABUSHIKI KAISHA
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 18:
19. An optical system with a fixed focal length comprising:
a front lens unit closest to an object side;
a rear lens unit having a negative refractive power closest to an image plane; and
a middle group having a positive refractive power as a whole, including two lens units, and disposed between the front lens unit and the rear lens unit,
wherein a distance between adjacent lens units changes during focusing,
wherein the two lens units in the middle group move on different trajectories during focusing,

wherein the front lens unit includes a negative meniscus lens having a convex surface facing an image side,
wherein the rear lens unit includes two or more positive lenses, and
wherein the following conditional expressions are satisfied:

—0.40≤f/fr≤−0.12

65≤vdpl 

0.00<|fpl/fr|≤0.60, where f is a focal length of the optical system, fr is a focal length of the rear lens unit, and vdpl and fpl are an Abbe number and a focal length of a positive lens having the largest Abbe number in the rear lens unit, respectively.