Well, at a guess: Focal length (given in the quoted post) is 16.5M. Diameter of the mirror is 200", which is pretty close to 5M. That makes the f-stop somewhere close to 3.3 by my calculation.
On Wed, Jul 29, 2009 at 10:44:11PM -0400, Desjardins, Steve wrote: > 16500? The obvious question: What's the max aperture in f stops? These > will be my fun facts for the day ;-) > > I wondered about the bokeh being donuts, but I like the idea of using the > "donuts of confusion" to focus the telescope. > ________________________________________ > From: [email protected] [[email protected]] On Behalf Of Matthew Hunt > [[email protected]] > Sent: Wednesday, July 29, 2009 5:28 PM > To: Pentax-Discuss Mail List > Subject: Re: K-7 new firmware 1.01 > > 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. > > -- > 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. -- 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.
