| Abstrakt: |
The Abbe prism employs a 90° roof so as to give image erection without displacing or deviating the optical axis. However, one disadvantage of this prism is that it divides each ray pencil into two fractions, which undergo opposite orders of reflection at the two roof surfaces. This leads to the formation of a double image whose relative splitting depends on the error in the roof angle, which therefore requires high manufacturing precision. This paper is concerned with the development of a non-roof prism that could replace the Abbe prism. The general solution of the prism design is discussed, and this is reduced firstly to a family of symmetrical prisms. The problem is then further reduced to give a solution specifying a set of symmetrical prisms having rectangular pupils centred on the optical axis. Finally, an 'optimum' solution is presented which employs total internal reflection at all four reflecting surfaces, and has a square entrance aperture centred on the incident optical axis. |
