Custom penta prisms

Penta Prisms, Polished and Mirror Coated in Rye

Kingsview Optical makes custom penta prisms to your drawing for rangefinders, alignment instruments, viewfinders and laser systems. We polish the faces to tight angles, mirror-coat the reflecting faces and AR-coat the transmitting faces in our own chambers, then check every angle on an autocollimator.

  • Made in Rye, East Sussex
  • Angles checked by autocollimator
  • Coated in-house
  • ISO 9001:2015
Send Your Prism Drawing See the Specification
Custom penta prisms made by Kingsview Optical in Rye, UK
Penta prisms, polished and coated in Rye.
Prisms made here, start to finish. Shaped, polished, coated, cemented and measured at our site in Rye.
See how we make them →
The basics

What a Penta Prism Does

In short: a penta prism is a five-sided prism that turns a beam through exactly 90° using two internal reflections. The deviation stays at 90° even if the prism tilts slightly, and the image is neither inverted nor reversed.

The two reflecting faces sit at 45° to each other, so the angle between the beam going in and the beam coming out is fixed by the prism itself, not by how accurately it is mounted. That makes a penta prism the standard choice wherever a true right angle matters: optical squares, rangefinders, alignment tools and laser levelling.

The reflections inside a penta prism happen at angles below the critical angle, so the two reflecting faces must be mirror coated. We usually use protected aluminium or silver, then blacken the coated faces to protect them. The entry and exit faces get an AR coating for your wavelength.

Because the angles between the faces set the deviation, they are the tolerance that matters most. We polish the faces on angle jigs and check them on an autocollimator. A penta prism with a roof replacing one face is a roof penta prism, used in camera viewfinders; see our roof prism page.

Penta prism: two reflections turn the beam through a constant 90°.
ObjectFPenta prismImageF
Two reflections keep the image the right way round.
Applications

Where Our Penta Prisms Are Used

RangefindersConstant-deviation optics that keep the measurement independent of small mount errors.
Alignment and surveyingOptical squares and alignment tools that set out a true right angle.
Laser levelling and squaringTurning a laser beam through 90° without drift as the instrument moves.
ViewfindersFolding the view through 90° with a correct, upright image.
MetrologyAutocollimation and flatness measurement set-ups.
Defence and securitySighting optics where the line of sight must stay fixed.
Specification

Penta Prism Specification

These are our standard tolerances. If your design needs tighter, tell us which parameter. We'll tell you plainly whether we can hold it, and what it adds to cost.

Size range0.8mm micro prisms to over 100mm
Dimension tolerance±0.1mm
Angle tolerance±3 arcmin standard, tighter on request
Deviation90° constant, set by the prism angles
Reflecting facesProtected aluminium or silver, blackened over the coating
Flatnessλ/4 @ 633nm
Surface quality (scratch-dig)60/40 standard, 40/20 on request
MaterialsSchott, Ohara and CDGM optical glass; fused silica
CoatingsMirror coating on the two reflecting faces; broadband AR, V-coat or MgF2 on the entry and exit faces
FinishingBlackened edges, protective chamfers, steps, bevels, drilled holes

Not sure what to specify? For a penta prism, the angle between the two reflecting faces sets the 90° deviation, so tell us the deviation tolerance your system needs and we'll set the face angles to suit.

Options

Made to Fit Your System

CoatingsMirror coatings on the reflecting faces and AR on the entry and exit faces, all coated in our chambers
Edge featuresProtective chamfers, steps, bevels and blackened faces, CNC shaped to suit your mount
Mounts and housingsPrism mounts and housings from our own machine shop Cementing and assemblyPenta prisms fitted into mounts and instrument assemblies
Questions

Penta Prism Questions

Why does a penta prism give a constant 90 degree deviation?
Because the beam reflects off two faces that are fixed at 45° to each other. If the prism rotates slightly, both reflections change together and the errors cancel, so the beam still leaves at 90°. A single mirror or right angle prism doesn't have this property.
Does a penta prism invert the image?
No. With two reflections, the image is neither inverted nor reversed, so it stays the right way round.
Why do penta prisms need mirror coatings?
The beam meets the two reflecting faces at angles below the critical angle, so total internal reflection doesn't happen. Those faces need a metal or dielectric mirror coating. We coat them in-house and usually blacken over the coating to protect it.
What angle accuracy can you achieve on a penta prism?
Our standard angle tolerance is ±3 arcmin, and we can go tighter for constant-deviation work. We check prism angles on an autocollimator with OEG software. Tell us the deviation tolerance you need and we'll confirm what we can hold.
What is a roof penta prism?
A penta prism with one reflecting face replaced by a roof, two faces at 90°. The roof adds an extra reflection, which is used in camera viewfinders to give an upright, correct image. We make these too; see our roof prism page.
What do you need to quote a penta prism?
A drawing with the aperture, face angles and deviation tolerance, the glass type, the mirror and AR coatings you need, and quantities for prototype and production.

Other Prisms We Manufacture

Right angle Penta Roof Dove Risley Optical wedges PSPolarizing cubes

Or see our full optical prism manufacturing capability, and our optical design service if you need help choosing or designing a prism.

Getting a Quote for Penta Prisms

Send us your prism drawing. An engineer from the team that would make your prisms, not a sales team, will review it. They'll tell you plainly what's achievable and what will drive cost.

What to send

  • Drawing (PDF or ISO 10110) with dimensions and angles
  • Glass type, or the wavelength range if you're not sure
  • Deviation and angle tolerances
  • Mirror coating, AR coating and wavelength range
  • Quantities: prototypes and expected production volumes

What happens next

  1. An engineer reviews itWithin one working day, flagging anything that will drive cost or lead time.
  2. We quote the prismFor the prototype, and for production at your volumes.
  3. We make, measure and deliverAll in Rye, with inspection data if you need it.
Start Your RFQ

Need a Custom Penta Prism?

Send your drawing, or describe what the prism needs to do. We'll tell you plainly how we'd make it, what it will cost and how long it will take.

Send Your Prism Drawing Call 01797 226202
Made in Rye, East Sussex. NDA-friendly. Defence and security work welcome. ISO 9001:2015.