Patent ID: 7769283

Claim:
A lens apparatus comprising: an imaging optical system including a focus lens unit; a branching optical unit disposed at an image side of the focus lens unit; a focus-state detecting unit that detects a focus state by using light beams from the branching optical unit; an actuator that drives the focus lens unit in an optical axis direction of the focus lens unit; a controller that controls the driving of the actuator, in accordance with an output from the focus-state detecting unit; a stop unit disposed between the focus lens unit and the branching optical unit; a stop value detector that detects a stop value of the stop unit, wherein the controller changes focus detection precision of the focus-state detecting unit in accordance with the stop value detected by the stop value detector; and an extender optical system that is disposed at the image side of the branching optical unit and that is insertable into and removable from a light path of the imaging optical system, wherein the controller changes the focus detection precision of the focus-state detecting unit in accordance with the insertion of the extender optical system into or the removal of the extender optical system from the light path of the imaging optical system.