Apparatus and methods employing a PDAF optical system are disclosed herein. An example apparatus includes an image sensor comprising a plurality of pixels. The plurality of pixels include a set of pixels configurable to be imaging pixels or focus pixels. The image sensor is configured to generate image data of a scene based on received light at the plurality of pixels. The example apparatus also includes a processor coupled to the image sensor. The processor may be configured to receive first image data of a first frame of the scene, determine at least one region of interest or region of non-interest of the first frame, select, based on the determined at least one region of interest or region of non-interest, a subset of the set of pixels to be focus pixels, and cause the selected subset of the set of pixels to operate as focus pixels.