Optical system and head mounted display

An optical system, comprising:

• a display screen (4), and a third lens (3), a second lens (2) and a first lens (1) arranged successively along a propagation direction of incident light,
• wherein an effective focal length f1 of the first lens (1) and an effective focal length f2 of the second lens (2) are both greater than an effective focal length f of the optical system,
• the third lens (3), second lens (2) and first lens (1) are arranged at a light exit side of the display screen (4), in the propagation direction of the incident light emitted from the display screen (4), and used to project the incident light into the human eye (5) for imaging,
• the first lens (1) and the second lens (2) are glued together, the two glued surfaces of the first lens (1) and the second lens (2) are both Fresnel surfaces,
• the first lens (1), the second lens (2) and the third lens (3) are located on a same optical axis,
• the first lens (1) comprises a first surface (11) and a second surface (12), and the second lens (2) comprises a third surface (21) and a fourth surface (22), the second surface (12) and the third surface (21) are arranged adjacent to each other and both are set as Fresnel surfaces, and the first surface (11) and the fourth surface (22) are both convex surfaces,
• the thickness h1 at the center of the first lens (1) is 2 mm≤h1≤4 mm;
• the thickness h2 at the center of the second lens (2) is 3 mm≤h2≤5 mm;
• the thickness h3 at the center of the third lens (3) is 2 mm≤h3≤4 mm,
• a spacing T1 is provided between the first lens (1) and the second lens (2), and the spacing T1 is set to 0.1 mm≤T1≤0.5 mm;
• a third spacing T2 is provided between the third lens (3) and the display screen (4), the third spacing T2 is set to 8 mm≤T2≤15 mm;
• a spacing Y is provided between the second lens (2) and the third lens (3), and the spacing Y is set to 2 mm≤Y≤4.5 mm;
• the spacing Y and the aperture x of the third lens (3) satisfies the following relationship:
• Y=ax+b, where −0.8≤a≤−0.39, 30≤b≤35.