Amici Prisms

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An Amici roof prism is a special prism that is meant to deviate a beam of light by ninety degrees while inverting the image. Shaped like a right angled prism whose hypotenuse has been replaced by a 90 degree TIR roof, these prisms are often used in the eyepieces of telescopes, spotting scopes and other optical instruments. They can be used in conjunction with other prisms to achieve desired parity.

Light rays enter the prism through one short face and strike the reflecting surface of one of the roof faces, are reflected to the other roof face and then are reflected a third time out of the prism. Since they revert and invert an image as well as deviated the line of sight, they are very useful in applications where one would need to take a previously-inverted image, bend it through a ninety degree angle and turn it right side for a viewer.

Specifications for Amici Prism

These prisms are also called Amici prisms or right angle roof prisms. Manufacturing an Amici prism requires precise craftsmanship because the roof angle must be extremely precise. If there is more than 4 arc seconds deviation from 90° an unwanted double image will result. Shanghai Optics is well equipped to handle this, with state of the art production facilities and a rigorous testing process.

Shanghai Optics manufactures Amici roof prisms in a variety of sizes and coating options. These roof prisms are available uncoated, with single layer AR coating on entrance and exit faces, or with the roof faces of the prism coated to provide mirror surfaces. Mirror coatings enable the amici roof prism to deviate angles other than 90°without being limited by total internal reflection.

Our standard roof prisms are manufactured from BK7 grade A optical glass. This Schott Borosilicate crown glass is chemically stable amorphous glass and has a refractive index of 1.51680 at 587.5618 nm, at the yellow Helium line. It’s transmission range is 350nm to 2.5 μm, and it has uniform transmission throughout the visible range. BK7 has a Knoop hardness of 610 and is a thermal expansion coefficient of 7.1 x 10-6 K-1. Without a reflective coating, it will exhibit a reflective loss of 8.1% at 587.5618 nm. BK7 glass is ideal for use in amici roof prisms because it requires no special handling and is stable over all normal operating conditions.

Our factory standard is a dimension tolerance of +/- 0.2mm. This enables an exact fit in any mounting, but if tighter specifications are required for applications in a particularly harsh environment, please call us to discuss our manufacturing limit for tolerances.Our prisms are made of highly polished glass, and our quality testing division ensures that every prism meets high standards of angle tolerance, dimension tolerance, surface quality, and flatness.

The flatness of any of our amici roof prisms is guaranteed to be at least λ/4 at 632.8 nm, and the clear aperture for our factory standard optics is greater than 80%. Our standard surface quality is 60-40 scratch and dig, and our amici roof prisms have an angle tolerance of ± 3arcmin.

Factory Standard 

Material: BK7 Grade A optical glass
Dimension Tolerance:+0,-0.2mm
Flatness: λ/4 at 632.8 nm
Surface Quality: 60-40 scratch and dig
Clear Aperture: >80%
Bevel: 0.2 mm to 0.5 mm x 45o
Angle Tolerance: ± 3arcmin

Part no.    A(mm)    B(mm)    h(mm)
RFP0101    27.4    20.0    20.0
RFP0102    41.1    30.0    30.0



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