Penta Prisms
Penta prisms deviate beams of light by a constant of ninety degrees. In imaging applications, the penta prism maintains the original orientation and does not reverse the image.
Standard penta prisms are used in image erecting assemblies, laser insertion prisms for range-finding, and advanced surveillance. Their fixed deviation, unaffected by slight rotations, makes them valuable for precise applications where exact alignment is challenging. This stability ensures a clear image despite minor movements. At Avantier, we produce custom prisms for metrology, surveillance, range finding and many other applications.
How a Penta Prism Works
A penta prism has two transmitting faces, arranged at a ninety-degree angle, and both entrance and exit faces are typically coated with anti-reflection coating. It also has two mirror faces coated with reflective coatings and one face between the two mirror faces that has no optical function except to join the two mirrors. Because the beams are incident at an angle less than the critical angle, the reflections are not due to total internal reflection. Instead, metallic or dielectric coatings are applied to the two reflective faces to create mirror surfaces. A beam of light will enter the first transmissive face and be reflected on the first mirror, be transmitted within the prism to the second mirror, and then be reflected from that out of the second transmissive face.
The geometry of these prisms requires coating the reflecting surfaces. The reflective coating is often aluminum, which may be coating with a protective coat of black paint overcoat.
Benefits
Some benefits of incorporating a penta prism into your optical system include:
- No inversion or reversion
- Insensitive to alignment
- Exact 90 degree deviation
They are a great choice when you want to turn a beam of light by precisely degrees, irrespective of the exact orientation of the prism. An alternative to the prism would be three mirrors, placed in a configuration called “the pentamirror”. Either a prism or mirror will deviate the light. But a penta prism is inherently much more stable than a pentamirror, and since light enters and exits the system only once it exhibits much better optical performance.
Roof Penta Prisms
A roof penta prism is often used in photography, especially in the viewfinder of single lens reflex cameras. This type of camera also includes a camera lens which produces an image that is reversed vertically and laterally, and a mirror which re-inverts it, removing the vertical reversion but leaving an image laterally reversed.
It is almost identical to a regular prism, with one key difference: one reflective face is replaced by a roof shape, where two surfaces meet at a ninety-degree angle. When this prism is used in an optical system, such as a single- lens reflex camera, the image is not only deviated ninety degrees it is also laterally reversed (returning to normal in the case of the camera).
Factory Standard
Material: | BK7 Grade A optical glass, Corning Fused Silica 7980, JGS1, JGS2 |
Dimension Tolerance: | +/-0.1mm |
90 Deviation Tolerance: | Precision series: up to 2 arc seconds |
Flatness: Precision series: | 1/4 l at 632.8 nm |
Reflectivity: | R > 95% per face from 630 to 680 nm |
Surface Quality: | 60-40 scratch and dig |
Coating: | On request |
Protective Bevel available |
Custom Penta Prisms at Avantier
Whether you need a penta prism, a roof penta prism, or any other custom optical component, our team here at Avantier is ready to help you find the perfect part. Our optical designers can assist in designing the ideal prism for your specific application, or if you already know what you need, we can fast-track the prototyping and manufacturing process to deliver it faster than any other custom optics provider. Our unparalleled supplier network, extensive in-house manufacturing equipment, and state-of-the-art metrology enable us to produce almost any part you might require. Please contact us today to place an order or schedule an initial consultation.
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