Amici Prism

An Amici prism is an optical prism designed to turn light by a 90 degree angle while inverting the image. This non-dispersive prism is also known as an amici roof prism, a dachkanten prism, or a dach prism. Though this prism looks almost like a standard right-angled prism, it has an additional triangular piece (‘roof-shaped’) on the longest side. This roof shaped piece provides total internal reflection (TIR), which flips the image laterally.

The term amici prism is also sometimes used to refer to a dispersive prism made with two triangular prisms placed in direct contact. For this type of prism one of the triangles is typically crown glass (a medium dispersion glass) while the other is flint glass (higher dispersion). Since incident light is refracted at the first entrance and refracted again at the interface between the prisms it will leave the second prism at almost normal incidence. A dispersive amici prism is typically designed so that a specific wavelength (the center wavelength) will exit the prism parallel to the original beam, though off-set.  This prism is often used in spectrometers and hand-held spectroscopes. 

At Avantier, we produce custom prisms of many kinds, including dispersive amici prisms and non-dispersive amici prisms (amici roof prisms). We can manufacture prisms in many different sizes and with any coating desired.

Applications of Amici Prisms

Amici roof prisms are often found in the eyepieces of optical instruments such as telescopes, endoscopes,  spotting scopes, and profile projectors. They can be used to take an inverted image produced by other optical components, turn it right side up, and bend it at a ninety-degree angle. This makes them extremely useful in many situations. Amici prisms are often used with other prisms 

Manufacture of Amici Prisms

When an amici roof prism is in use light will enter the prism through a short face and hit the reflecting surface of one of the roof faces. The light will then be reflected off the other roof face and exit the prism through the second short face. Because of this, the roof angle of an Amici roof prism must be highly precise; just four arc seconds deviation from a perfect right angle will result in double images. Careful craftsmanship and thorough testing are required to manufacture quality Amici prisms, and not every optical supplier is up to the task.

 At Avantier, we pride ourselves on our high-quality machinery and state-of-the-art metrology that allows us to manufacture precision custom optics, including custom amici prisms built to order.  Amici prisms are typically cut and ground from premium borosilicate crown glass, but there are other substrate options available on request. Avantier standard surface quality is 60-40 scratch and dig, and our optical engineers ensure that the roof angle of our amici roof prisms are accurate to  3arc min.

Factory Standard


BK7 Grade A optical glass

Dimension Tolerance:



λ/4 at 632.8 nm

Surface Quality

60-40 scratch and dig

Clear Aperture:



0.2 mm to 0.5 mm x 45o

Angle Tolerance:

± 3arcmin

Custom Amici Prisms at Avantier

Whether you need an amici roof prism made to order for your telescope or endoscope,  a dispersive amici prism for your spectroscope, or any other custom prism for your optical assembly, we have you covered. If you would like an Amici roof prism but need your light bent by an angle other than 90 degrees, we can use mirror coatings to get you there. Please contact us today to place your custom order or schedule an initial consult.


Contact us NOW for sales & expert advice.