Optical system and display apparatus

An optical system through which a light beam from an image display element is guided to an exit pupil, the optical system comprising:

• a first transmissive reflective surface and a second transmissive reflective surface that are disposed in order from an exit pupil side to an image display element side;
• and
• a first optical element and a second optical element that are disposed in order from the exit pupil side to the image display element side,
• wherein the first optical element includes a first optical part made of a first optical material, and a second optical part made of a second optical material different from the first optical material that are disposed in order from the exit pupil side to the image display element side,
• wherein the first optical part and the second optical part are cemented to each other and a diffraction grating is formed on a cemented surface of the first and second optical parts, and
• wherein the following inequality is satisfied:
• 1
• ⁢
• 0
• ⁢
• 0
• ⁢
• 0
• <
• H
• ×
• N
• <
• 1
• ⁢
• 0
• ⁢
• 0
• ⁢
• 0
• ⁢
• 0
• where H [μm] is an average grating height of the diffraction grating and N is the number of annuli of the diffraction grating.