Roof Prism
Roof Prism
A roof prism, also known as an Amici prism, is a right-angle prism that deviates light by 90 degrees while inverting the image both left-to-right and top-to-bottom. The hypotenuse face of a conventional right-angle prism is replaced by a 90-degree roof structure utilizing total internal reflection (TIR). Glass that does not contribute to the clear aperture has been trimmed away to reduce size and weight.
The roof prism design enables straight-line optical alignment between objective and eyepiece lenses. This makes roof prism binoculars more compact and streamlined than Porro prism designs, and easier to seal against moisture and dust. The trade-off is manufacturing complexity—the 90° roof edge must be produced with exceptional precision, and high-quality coatings are required to maintain image quality. Polarization states may rotate during reflection through the prism.
Star Optics manufactures roof prisms in N-BK7, H-K9L, and fused silica, with dimensions from 2mm to 80mm.
Applications
Roof prisms are used in binoculars and spotting scopes where compact straight-tube design is desired. They serve as image-erecting elements in terrestrial telescopes, providing correctly oriented views. In optical instruments such as rangefinders and surveying equipment, roof prisms provide 90-degree beam deflection with image correction in a minimal package. They are also used in laser systems when right-angle deflection is needed with compact geometry.
Specifications：
| Parameter | General Spec. | High Precision Spec. |
|---|---|---|
| Material | Optical glass (H-K9L, BK7), Fused silica | |
| Dimension | 2mm ~ 80mm | |
| Dimension Tolerance | ±0.1mm | ±0.02mm |
| 90° Deviation Tolerance | < 3 arc min | < 3 arc sec |
| Surface Flatness @ 633nm | λ/2 | λ/4 |
| Surface Quality | 60-40 | 20-10 |
| Coating | Upon customer’s request | |
Customization
Star Optics offers custom roof prisms with phase-correction coatings for polarization-sensitive applications. Each Amici prism is inspected for roof edge quality and angular accuracy. Contact us to discuss your requirements.
