A penta prism is a five sided optical reflecting prismthat consistently defines a right angle. It reflects light inside the prism twice, and is used to deviate a beam by a constant ninety degrees.

Standard penta prisms have applications in image erecting assemblies, and are used as laser insertion prisms for range-finding and advanced surveillance.  The deviation provided by these optical devices don’t change when the prism is rotated slightly, which makes them valuable for situations where a precise deviation is necessary but precise alignment impossible or difficult. This same property gives it stability and allows it to provide a good image in spite of slight movements.

Since the beams are incident at an angle less than the critical angle the reflections are not caused by total internal reflection. Instead, metallic or dielectric coatings are applied to the two reflective faces to provide mirror surfaces.  Shanghai Optics provides penta prisms with aluminum or enhanced aluminum coatings. Black paint surfaces are sometimes used to increase reflection.

Variations on penta prisms include half penta prisms, which deviate a beam by forty five degrees, and roof penta prisms, which reverse the parity of the image.

Specifications for Standard Penta Prisms

Shanghai Optics uses state of the art metrology equipment to measure the accuracy of the 90 degree azimuthal beam deviation. Our precision instruments allow us to keep deviations very low, and we can work with you to produce highly precise penta prisms that meet any standard.

While our standard series has a 90° deviation tolerance of less than 10 arc seconds, the precision series has no more than a 2 arc second deviation.  Our standard series has flatness of l/2 l at 632.8 nm, while the precision series offers a flatness of up to l/4 l @ 632.8 nm. Surface quality of our standard line is 60-40 scratch and dig.

Our Penta prisms are available in BK7 Grade A optical glass, corning fused silica 7980, JGS1, and JGS2.

BK7 Grade A optical glass (optical borosilicate-crown) is an ideal all-purpose optical substrate. It has a clear, practically colorless appearance, and a very high refractive index homogeneity.  It performs well in chemical tests and no special handling are required.

Corning Fused Silica 7980 is high purity synthetic amorphous silicon dioxide. It is manufactured by flame hydrolysis, and has a very low thermal expansion coefficient. It is also a colorless non-crystalline substance, and is especially well suited for ultraviolet transmission.

JGS1 is high quality ultraviolet grade fused silica and is transparent in UV and Vis ranges. In the interval of 2600-2800 it has an intensive OH absorption band. JGS1 penta prisms are suited for deep UV and visible. This optical glass has essentially no bubbles or inclusions.

JGS2 is ultraviolet grade fused silica similar to JGS1. Micro prisms will be bubble free, but larger pieces may contain bubbles or inclusions, so it is best used for applications which are non-sensitive to such issues.

Our design team would be happy to work with you to design custom penta prisms and other optical systems that meet the needs of your application.

Factory Standard

• Material: BK7 Grade A optical glass, Corning Fused Silica 7980, JGS1, JGS2
• Dimension Tolerance: +/-0.1 mm
• 90° Deviation Tolerance:
  Standard series: < 10 arc seconds
  Precision series: up to 2 arc seconds
• Flatness:
  Standard series: l/2 l at 632.8 nm
  Precision series: up to l/4 l @ 632.8 nm
• Reflectivity: R > 95% per face from 630 to 680 nm
• Surface Quality: 60-40 scratch and dig

Contact us for manufacturing limit or custom specifications.