On an early autumn day of 1608, Hans Lipperhey, a spectacle maker from Middelburg, in the Netherlands' coastal province of Zeeland, applied before the States General of The Hague  for a patent on an "instrument for seeing far". By that time, use of small rounded glass disks to aid the natural eyesight wasn't new. Those bulging out on both sides, resembling lentil - or "lens" in Latin - have been used to correct for farsightedness since the mid 13th century. But this was the beginning of something else. In the summer of 1609, Galileo, Harriot, and others, turned the new Dutch invention - the "spyglass" - toward the night sky. The telescope was born.

This tale grew old, but our fascination with telescopes has not. The following text is an attempt to give more of an insight into their inner workings. More specifically, how do they form images and what factors determine their quality. Somewhat unusual, the main aspect is that of the optical wavefront, as opposed to the geometric (ray) "interface". That deliberate choice, while perhaps somewhat less convenient, should throw more light at the underlying physical fundamentals. Main reference sources are as follows: (1) Astronomical Optics, Daniel J. Schroeder, (2) Aberration Theory Made Simple, Virendra N. Mahajan (3) Optics, Eugene Hecht, and (4) Telescope Optics, Harrie Rutten and Martin van Venrooij. Most of raytracing plots and routine checkups are by ATMOS, Massimo Riccardi, and OSLO, Lambda Research Corporation. Most of diffraction patterns were generated by Aberrator, Cor Berrevoets.

3. TELESCOPE ABERRATIONS: Types, causes
3.1. Wavefront aberrations
3.2. Ray (geometric) aberrations
3.3. Conics and aberrations 2
3.4. Terms and conventions
3.5. Aberration function, Seidel 

 5. INDUCED ABERRATIONS
5.1. Air-medium errors Turbulence
5.2. Alignment errors
5.3. Forced surface errors

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Web published on July 14. 2006. by Vladimir Saček