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Right Angle Prisms

Right angle prisms are generally used to change the direction of light by 90° or 180° dependent on which surface the incident beam is directed at. This is due to the light undergoing total internal reflection (TIR) within the prism before exiting.

Knight Optical offers custom right angle prisms for customers requiring a component that differs from our stock range. We are able to help with any volume order and have often been involved in projects from prototype through to bulk orders, working closely with our customers on finalising the details of the optical component to ensure they fit seamlessly into their applications.

Below are our typical manufacturing capabilities, we offer right angle prisms in Schott and equivalent glass types such as BK7, as well as more specialist materials including UV or IR fused silica and crystalline materials such as calcium fluoride and zinc selenide, more information on these can be found on our infrared page.



Angular tolerances

Surface Figure


Right Angle Prism

2mm to 100mm+

< 1 arcminute

< 0.5 fringe

< 60/40

Coatings can also be applied to either the small faces or the hypotenuse dependent on the end application. Our current stock precision right angle prisms have different coating options which can be applied to your custom order:

  • Antireflective (AR) coating: Antireflective coating on both short faces to achieve optimal performance. The coatings can be broadband to encompass a large wavelength range.
  • Protected mirror coating: mirror coating and optical black paint on the hypotenuse to achieve high internal reflection over a greater angular range.
  • External reflector range: protected mirror coating on hypotenuse for use as a mirror.

Contact our technical sales team and discover how Knight Optical’s high quality custom right angle prisms and service can improve your instrumentation and supply chain

Additional Information

  • A right angle prism is a deviation prism, it changes the path of the incident beam (via TIR). However, the returned image is is either left- or right-handed dependent on whether the light is deviated by 90° or 180° respectively.
  • Total internal reflection (TIR) occurs when the incident ray enters the prism, passing straight through with no refraction, then hits the glass-air boundary at a 45° angle which is larger than the critical angle (approximate 42° in glass). This leads to the phenomenon TIR of the light ray which is completely reflected by 90° and exits straight through the prism with no further refraction.
  • Right angle prisms are often used in place of plane mirrors due to their ease of mounting and alignment within a system.
  • Generally when the light is deviated through the prism by 180° it is more commonly known as a porro prism and often used in pairs to revert the image back to its original orientation within a system.


Knight Optical offer a variety of coatings which can be applied to the surface of your right angle prism.
These include:

  • Antireflective (AR) coatings such as BBAR.
  • Mirror coatings for UV, visible and IR wavelengths.
  • Protective black optical paint to enhance the reflection off the back surface.

Quality Assurance

In our metrology laboratory our technicians check your optical components against their given specification. This testing includes:

  • Angular dimensions which are checked on our Trioptics PrismMaster which is accurate down 3 arc seconds.
  • The surface flatness or irregularity measured on our Zygo Verifire interferometer.
  • Optical coatings verification on our Agilent Cary 7000 Spectrophotometer which can perform
    spectral scans at multiple angles of incidence and different polarisations.

All optics are 100% visually inspected before packaging, our staff are trained to ISO 10110 and MIL-0-13830A, and can check down to 10/5 scratch/dig which is especially critical for lenses used in laser applications.

Our 2022/2023 Catalogue

Inside Knight Optical’s catalogue you’ll find details of the industries we serve as well as the many other services we can offer. It also showcases hundreds of our most popular products, supported by useful technical information, to help you choose the right part for your application.
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