Penta Prism

A penta prism is a five sided reflecting prism used to deviate a beam of light by a constant 90 even if the entry beam is not at 90.  At Avantier, we produce custom penta 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 antireflection 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. 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 be reflected from that out of the second transmissive face. 

The reflective coating is often aluminum, which may be coating with a protective coat of black paint. 

Benefits of a Penta Prism 

Some benefits of incorporating a pent prism into your optical system include:

  • No inversion or reversion
  • Insensitive to alignment
  • Exact 90 degree deviation

A penta prism is a good choice when you want to turn a beam of light by  precisely  90 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 pentaprism

A roof pentaprism is a variant of the pent prism, and is often used in photography, especially in the viewfinder of single lens reflex camera. 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. 

A roof pentaprism is almost identical to a regular penta prism, with one key difference: one reflective face is replaced by a roof-shape, with two surfaces meeting 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 90 degrees, it is also laterally reversed (in the case of the camera, back to normal).

Factory Standard


BK7 Grade A optical glass, Corning Fused Silica 7980, JGS1, JGS2

Dimension Tolerance:


90 Deviation Tolerance:

Precision series: up to 2 arc seconds

Flatness: Precision series:

1/4 l at 632.8 nm


R > 95% per face from 630 to 680 nm

Surface Quality:

60-40 scratch and dig


On request

Protective Bevel available

Custom Penta Prisms at Avantier

Whether you need a penta prism, a roof pentaprism, or any other custom optical component, the team at Avantier is ready to help you with the perfect part. Our optical designers can help you design the ideal prism for your specific application, or if you already know what you want we can fast track the prototyping and manufacturing process to get you what you need in better time 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 need. Contact us today to place an order or schedule an initial consultation.


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