| The diffraction pattern, which is the image of a star, of a telescope can be changed considerably by using different aperture shapes in combination with appropriately shaped occulting mask on the optical axis. The improvement, or lack thereof, in the resolution of UNR's 16"-f/11 cassegrain telescope caused by different shaped obstructions on the optical axis and different shaped aperture stops is discussed. Photographic results obtained at the telescope, using Polaris ((alpha)-UMin) as the test system, give good agreement with the theoretical calculations. The theoretical intensity distribution for an unobstructed circular aperture of unit (1) diameter is used as the comparison standard for the theoretical calculations of the diffraction pattern. Polygonal aperture and mask shapes studied were the circular, triangular, square, pentagonal, and hexagonal. A special section on non-polygonal (non-angled) aperture and mask shapes, using Sonine type diffraction integrals to define the shapes, is included. A combination of square aperture and square mask produced the best clear sharp images of the Polaris system, while a combination of Sonine type aperture and mask produced the largest separation distance between Polaris and Polaris B. |
