The Porro prism is an optical component commonly used in handheld binoculars, which corrects the inverted image formed by the objective lens through the principle of total internal reflection. Its cross-section is an isosceles right triangle, offering advantages such as low cost and no phase difference, but it has the limitation of being relatively large in size.

Core Structure and Optical Principle of the Porro Prism

• Structural Features: Composed of two mutually perpendicular right-angle faces, with a cross-section forming a 45°-45°-90° isosceles right triangle. Incident light undergoes two total internal reflections, rotating by 180°, achieving image correction.
• Optical Path Characteristics: Parallel light enters the objective lens and converges, undergoes four consecutive reflections through the Porro prism, focuses on the focal plane, and then diverges into parallel light through the eyepiece. The imaging process is free from phase difference and double-image aberration.

Performance Advantages and Limitations of the Porro Prism

Advantages

• Low Cost and Easy Manufacturing: No reflective coating is required; only an anti-reflective coating on the hypotenuse face is needed, resulting in low manufacturing costs, making it suitable for low-end products.
• Stable Optical Performance: Free from double-image aberration and phase difference, it can achieve better imaging quality than roof prisms at the same cost.
• Robust Structure: The use of Porro prisms in binoculars enhances impact resistance.