On Wed, Jul 29, 2009 at 5:13 PM, Desjardins, Steve<[email protected]> wrote:
> OK, but I bet the bokeh sucks on the Hale. Yes, it's definitely "donut" bokeh, complete with obstructions from the secondary supports. Furthermore, given its age, the mirror figure is maintained by a mechanical system of springs and sliding weights that "tug" it into the correct figure as it points in different directions. When I was there, these contraptions had a tendency to bind up, distorting the figure and making the "bokeh" asymmetric and splotchy. Mike Johnston would not have approved. Fortunately, even with the 16,500-mm focal length, all of our subjects were "at infinity". The only time we had to see the "bokeh" was when the telescope was badly out of focus, such as at the beginning of a run when it had just been installed. Then the focal plane might be a whole millimeter or two out of position! We would point to a bright star, measure the diameter of the "donut" image, and calculate from that how far to move the focus. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
