Projection display apparatus

A projection display apparatus, comprising:

• a light valve configured to modulate illuminating light, based on image data, to generate the modulated illuminating light;
• an illuminating unit that includes a light source, and a plurality of optical members for illumination,
• wherein the plurality of optical members are configured to generate the illuminating light, based on light received by the plurality of optical members from the light source, to guide the illuminating light to the light valve;
• a projection lens configured to:
• project the modulated illuminating light received from the light valve to a projection surface, and
• allow detection light to enter from a first direction opposite to a second direction of the modulated illuminating light;
• and
• an imaging device configured to allow the detection light to enter through the projection lens,
• wherein the imaging device, at a first location, is optically conjugated with the light valve that is at a second location, and
• wherein at least one of the plurality of optical members has optical property that reduces a noise component which affects the detection light.