FOCUS DETECTION APPARATUS

A focus detection apparatus has a field lens on or in a vicinity of an anticipated focal plane of an imaging lens and a refocusing optical system arranged behind the field lens to focus light beams transmitted through different areas in a pupil of the imaging lens onto a photo-sensor array to form a secondary image thereon, and detects a focus in accordance with an output signal of the photo-sensor array. A filter which blocks an infrared ray and transmits a visible ray is arranged adjacent to the field lens to prevent degradation of a filtering characteristic which depends on an inclination of a main light impinging to the filter.