An optical system is disclosed which is for a display apparatus having a light source for emitting read light and a reflection type spatial light modulator for modulating the read light incoming thereto into in accordance with image written thereon. The modulated light is projected onto a screen by a projection lens to display the image. A field lens is provided between the modulator and screen at such a position that both the read and modulated light pass therethrough. The field lens focuses the modulated light on near an entrance pupil of the projection lens so that the intensity of the modulated light is increased.
