Detecting apparatus, image pickup apparatus, and detecting method

A detecting apparatus comprising:

• a memory storing instructions;
• and
• a processor configured to execute the instructions to:
• perform focus detection using a pair of focus detecting signals obtained from an image sensor that has a first pixel including a pair of photoelectric converters arranged in a first direction and a second pixel including a pair of photoelectric converters arranged in a second direction different from the first direction,
• detect flicker using a flicker detecting signal obtained from the image sensor, and
• control signal readout from the image sensor,
• wherein the processor is configured to switch between a first readout state for performing signal readout for generating the pair of focus detecting signals from each of the first pixel and the second pixel, and a second readout state for performing signal readout for generating the pair of focus detecting signals from a focus detecting pixel as the first pixel and for performing signal readout for generating the flicker detecting signal from a flicker detecting pixel that is either the first pixel or the second pixel and is different from the focus detecting pixel.