Image sensor and image capturing apparatus

An image sensor comprising:

• a first imaging pixel and a second imaging pixel each of which detects an object image formed by a photographing optical system and generates a recording image,
• wherein said first imaging pixel comprises a plurality of photoelectric conversion units segmented in a first direction and said second imaging pixel includes four photoelectric conversion units segmented in the first direction,
• the plurality of photoelectric conversion units configured to photoelectrically convert a plurality of images formed by split light beams passing through the photographing optical system and outputting focus detection signals used to detect a phase difference,
• a base-line length of photoelectric conversion units used to detect the phase difference out of the plurality of photoelectric conversion units included in said first imaging pixel is longer than a base-line length of photoelectric conversion units used to detect the phase difference out of the plurality of photoelectric conversion units included in said second imaging pixel, and
• images detected by two photoelectric conversion units at a center out of the photoelectric conversion units of each of the second imaging pixels are photoelectrically converted to output the focus detection signals used to detect the phase difference,
• wherein the base-line length is a separation distance between gravity centers of portions of the photoelectric conversion units included in each of said first and second imagining pixels, the portions being extracted in an exit pupil range of the photographing optical system.