Fixed-focus projection optical system

A fixed-focus projection optical system, provided with an object side and an image side arranged relatively along an optical axis direction, comprising a micro-mirror array, an equivalent prism, a galvanometer, a first lens group, a second lens group, a plane mirror, and a curved mirror provided in sequence from the object side to the image side, wherein:

• the plane mirror is provided at one side of the optical axis, and the curved mirror is provided at the other side of the optical axis;
• the plane mirror is provided at an angle with the optical axis, and one end of the plane mirror is intersected with the optical axis;
• an optical power of the first lens group is positive, and an optical power of the second lens group is negative;
• and
• the second lens group is configured to move along the optical axis to focus the fixed-focus projection optical system in response to that a projection distance is changed.