| 摘要 |
PURPOSE:To eliminate variation in geometric optical property against variation in the wavelength of luminous flux and temperature variation by sticking two prisms together and allowing the wavelength fraction of a refractive index and variation in refractive index to satisfy specific conditional equations. CONSTITUTION:Two prisms 2A and 2B having refractive indexes n1 and n2 are stucked to form a composite prism 2, on which luminous flux is incident at an angle theta1 and projected vertically from the projection surface of the prism. Wavelength fractions of the refractive indexes are denoted as DELTAn1 and DELTAn2 and an equation I derived from a Snell'slaw sintheta1=n1sintheta2 is condition that an angle of projection, i.e. vertical projection does not vary according to wave length variation. An equation II obtained by substituting the fractions in said equation with refractive index variations DELTAnT1 and DELTAnT2 withtemperature is the condition that the angle of projection does not vary with temperature. There fore, the light is projected vertically from the projection surface even if the luminous flux has wavelength variation and temperature variation. |
