English
Based on the right-angle prism, by dividing the hypotenuse into two surfaces and elevating them to form a roof shape, with the two divided surfaces being mutually perpendicular, we obtain the roof right-angle prism. The optical path of the roof right-angle prism is illustrated below. The light beam entering the prism undergoes a deflection at the roof, which swaps the left and right portions of the image, before exiting the prism.
The roof prism is known for its smaller size and the ability to align the objective lens and eyepiece in a straight line, making it commonly used in extremely compact binoculars. Compared to the Porro prism, the roof prism has two main disadvantages:
Greater Light Loss: The roof prism causes more light loss, resulting in a darker image.
Higher Assembly Precision Requirement: It is more difficult to manufacture due to the higher precision required, making it more expensive. High-quality roof prisms can match, but generally do not exceed, the performance of Porro prisms.
| Material | BK7 glass / UV Fused silica |
| Dimension | 3mm~200mm |
| Dimension tolerance | ±0.1mm~±0.05mm |
| Surface quality | 60/40, 40/20, 20/10 |
| Surface flatness | λ/20 – λ/4 |
| Angle tolerance | <30arc sec. ~5arc min |
| Bevel | <0.25mm×45° |
| Coating | As per customized request |
Structural Features:
The roof prism consists of two mutually perpendicular reflecting surfaces, known as the roof surfaces. This design allows the roof prism to add one reflection without changing the direction of the optical axis and the imaging direction in the main section, thereby changing the total number of reflections from odd to even, meeting the requirement for object-image similarity.
Optical Performance:
Light Loss: Compared to the Porro prism, the roof prism experiences greater light loss, resulting in a darker image.
Assembly Precision: The roof prism requires high assembly precision, making it difficult to manufacture and more expensive.
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