----------------------------------- Serban 26 Mar 2008 21:54 ----------------------------------- aici http://www.skyandtelescope.com/howto/diy/3306876.html zice asta: " Coma makes stars appear asymmetric even if the telescope is perfectly focused — the farther the star is from the center of the focal plane, the worse it gets. In particular, this aberration can dramatically reduce the clarity of planetary detail. Surprisingly, the size of the "sweet spot" depends only on the main mirror's focal ratio (the mirror's focal length divided by its diameter) and not its size. For instance, even a perfect f/4.5 mirror, small or large, can provide "diffraction limited" performance only within a 2-millimeter (0.08-inch) circle at the focal plane. An f/10 paraboloid's sweet spot, by contrast, spans 22 mm (0.87 inch). (For the mathematically inclinded, the sweet spot's diameter is proportional to the cube of the f/ratio.) " cam cat % din FOV acelui dobson 200 f/6 este afectat? devin foarte confuz.....