Visual system

A visual system, sequentially comprising from a first side to a second side along an optical axis:

• a first lens with a positive refractive power, wherein a first side surface thereof is a convex surface and a second side surface thereof is a flat surface;
• a reflective polarizing element;
• a quarter-wave plate;
• a second lens with a positive refractive power, wherein a second side surface thereof is a convex surface;
• a partially-reflective element;
• and
• a third lens with a positive refractive power, wherein a second side surface thereof is a convex surface;
• a position of the first lens on the optical axis relative to an imaging surface of the second side is fixed, and a distance of the second lens on the optical axis relative to the first lens is adjustable;
• there are three lenses with refractive powers in the visual system;
• and
• the visual system satisfies:
• 1.15≤fg/f2≤1.50 and 1.55<ΔL/Δf<2.1, where fg is a combined focal length of the first lens, the reflective polarizing element and the quarter-wave plate, f2 is an effective focal length of the second lens, ΔL is a movable distance of the second lens when the visual system is switched between a first state and a second state, and Δf is a difference between a total effective focal length when the visual system is in the first state and a total effective focal length when the visual system is in the second state.