Method for coupling narrow-band interference filters to two-mirror and catadioptric telescopes

摘要

A means for examining the sun in monochromatic light in which the separation of the mirrors of either a catadioptric, or pure two-mirror, telescope is altered to produce a virtual object for a converging lens, termed a "forcing lens," this lens being so located between the virtual object and a narrow-band, Fabry-Perot, etalon-type, interference filter, that the convergent beam of light from the telescope passes through the interference filter at a high focal ratio, relative to the telescope's conventional focal ratio, before it traverses the forcing lens, which in turn forms the optical system's only real image, at a different, and much lower, focal ratio. Image contrast is markedly enhanced, relative to the contrast obtained by the same telescope at its conventional focus. By means of a graduated series of entrance pupils, which may be generated by a graduated series of broad-band pre-filters, a step-wise-zoom, constant-contrast, solar monochromator may be constructed. Formulas are provided for parfocalizing a series of forcing lenses. By means of such a series, real-image height may be adjusted, allowing the optimization of an eyepiece/forcing-lens combination for viewing the solar disk and surrounding prominences simultaneously, out to a considerable distance from the solar limb.