Patent ID: 8249443

Claim:
An image pickup apparatus comprising an apparatus body including an image sensor built therein, and a lens unit detachably attached to an aperture opening on a front surface of the apparatus body, the apparatus body being provided with a back focus adjustment mechanism and a sliding member which intervenes between the aperture and the image sensor and is slidable in a direction perpendicular to an optical axis of the image sensor, the sliding member being provided with an infrared blocking filter and a dummy glass plate arranged next to each other along a sliding direction, the image pickup apparatus being capable of switching modes between a day photographing mode in which the infrared blocking filter is positioned on the optical axis of the image sensor and a night photographing mode in which the dummy glass plate is positioned on the optical axis of the image sensor, and the dummy glass plate having a thickness t 3 greater than a thickness t 2 with which optical path length extension equivalent to that with the infrared blocking filter having a predetermined thickness t 1 is obtained, wherein a back focus adjustment by the back focus adjustment mechanism at the time of switching from the day photographing mode to the night photographing mode is performed by moving the imaging plane position from a start point which is an imaging plane position set in the back focus adjustment in the day photographing mode to an end point which is further from the lens unit, and the back focus adjustment being performed with a procedure comprising searching an imaging plane position where the maximum focus evaluation value is obtained during said moving.