Abstract: Two reflective surfaces disposed in a predetermined angular orientation inside the optical tube assembly of a telescope intercept the optical beam and deliver it from the objective to the eye-piece. By translating these surfaces simultaneously along the axis bisecting the angle between them, the separation between the focal points of the objective and the eye-piece is adjusted as required to re-focus the telescope in a continuous and reversible fashion without changing its overall dimensions.

Abstract: A targeting unit is incorporated into the main body of a solar telescope. The targeting image is provided by an aperture facing the sun in the housing of the telescope through which sunlight is received and directed to a transmissive viewing screen placed in the housing on the same side of the telescope's eyepiece. All parts of the targeting system are fixed to the housing of the telescope and removed from accidental contact by personnel operating the telescope, thereby minimizing the chance for events that might cause misalignment. In addition, this configuration makes it possible to easily position both the viewing screen and the eyepiece on the same side of the telescope following any degree of folding of the objective beam.

Abstract: A solar filter assembly combines a high-precision Fabry-Perot etalon with a variety of conditioning filters judiciously selected to effectively block completely all radiation except for the spectral line of interest. In addition, a tuning mechanism is provided to precisely control the peak frequency of the filter's output by varying the optical length of the etalon's cavity.