Re: [Utah-astronomy] Saturday night at the Gravel Quarry
Bob wrote: <snip> > German Platero and myself were left. German had
just learned to use his Bino-viewer with a lot of help from Kurt Fisher and was having fun with it on his 12" Meade Cat.
German's difficulty was that when a f6.3 focal reducer is placed in an f/8-9 SCT, the generous range of back focus - for which SCT's are well known - decreases proportionately. With the focal reducer in place, the maximum back focus range could not be raised to the level of focal plane of a right-angle with binoviewer. Removing the focal reducer restored the SCT's default longer back focus range and then the binoviewer worked fine. I did not take a precise measurement, but guesstimate that with the 6.3 focal reducer in the place, the backfocus was limited to less than 120mm. Lesson learned: For those of you interested in buying a binoviewer for use with an SCT, be aware of this limitation. As far as the performance of binoviewer, I had a chance to compare M27 in Lowell's SCT with and without an O filter with German's SCT equipped with no filter and the binoviewer. The distinction between the two is the binoviewer splits the light in half but spreads it across two human wet-ware retinal detectors inside of just one organic "ccd" chip. The magnifications were not the same, but my impression was that the binoviewer without contrast filter met or exceeded the single eyepiece filter combination in terms of detectable visible contrast detail.
After 12:30, as everyone else left, as predicted by the Clear Sky Clock, we were treated a moonless crystal clear sky and a blazing Milky way and spent another two hours with spectacular views of numerous deep sky favorites.
After leaving at midnight and driving back to Salt Lake, as is my usual practice, I stopped at Little Mountain pass to give the current sky condition one last peek with binoculars. On stopping, I saw the same, clear, cloudless sky with good seeing that Bob described. M7 (Ptolemy's cluster), M6, M8 (Lagoon) and M24 (Small Sagittarius Star Cluster) were all naked-eye objects. Milky Way light cloud regions could be seen from Sagittarius through Cepheus. Theta-Rho Oph dark lanes could not be seen - too close to SLC light pollution gradient. Sky orientiation was typical for early July with the Milky Way spinward arm at 40 degs alt to the eastern horizon. Essentially, it was like a Unita class sky for seeing and transparency, reduced in contrast by SLC light pollution. The air was cold and still - I could easily see my breath during normal breathing. Pulling out 10x50 binos I was able to quickly tick off the basic Messier summer objects: the globs M10 and M14 in Oph; M22, M24, M17 in Sagittartius; M11,the Scutum Star Cloud and M27 and the Coathanger asterism in Sge; split Alberio; M29 in Cyg; the some of the outline of NGC7000 and Harrington 14 in Cyg; M52 in Cep; the Herschel's Garnet star in Cep - which was looking particularly garent that night; and ending with splitting the cat's eye wide double Drac 16-17. Really a quite amazing half-hour. Then I drove home (20 minutes), got out of the car and looked up to find the next incoming band of mid-altitude clouds directly overhead covering 20 percent of the sky. Lesson learned: This year may be "eastern" or "midwest" style observing. The opportunities will be in the leeward side of passing cloud fronts and last an hour or two. Plan to set up, read a book for a while until a cloud band passes, the sky opens up and "magic time" begins. - Kurt
Denkmeier has a .5 focal reducer made specifically for SCT's and I have had no problem using it on both an 8-inch and 14-inch Celestron SCT's with a 2" diagonal. It works great making an 8" SCT a wide field scope with pinpoint stars. -----Original Message----- From: utah-astronomy-bounces+djcolton=piol.com@mailman.xmission.com [mailto:utah-astronomy-bounces+djcolton=piol.com@mailman.xmission.com] On Behalf Of Canopus56 Sent: Sunday, June 08, 2008 4:55 PM To: Utah Astronomy List Serv Subject: Re: [Utah-astronomy] Saturday night at the Gravel Quarry Bob wrote: <snip> > German Platero and myself were left. German had
just learned to use his Bino-viewer with a lot of help from Kurt Fisher and was having fun with it on his 12" Meade Cat.
German's difficulty was that when a f6.3 focal reducer is placed in an f/8-9 SCT, the generous range of back focus - for which SCT's are well known - decreases proportionately. With the focal reducer in place, the maximum back focus range could not be raised to the level of focal plane of a right-angle with binoviewer. Removing the focal reducer restored the SCT's default longer back focus range and then the binoviewer worked fine. I did not take a precise measurement, but guesstimate that with the 6.3 focal reducer in the place, the backfocus was limited to less than 120mm. Lesson learned: For those of you interested in buying a binoviewer for use with an SCT, be aware of this limitation. As far as the performance of binoviewer, I had a chance to compare M27 in Lowell's SCT with and without an O filter with German's SCT equipped with no filter and the binoviewer. The distinction between the two is the binoviewer splits the light in half but spreads it across two human wet-ware retinal detectors inside of just one organic "ccd" chip. The magnifications were not the same, but my impression was that the binoviewer without contrast filter met or exceeded the single eyepiece filter combination in terms of detectable visible contrast detail.
After 12:30, as everyone else left, as predicted by the Clear Sky Clock, we were treated a moonless crystal clear sky and a blazing Milky way and spent another two hours with spectacular views of numerous deep sky favorites.
After leaving at midnight and driving back to Salt Lake, as is my usual practice, I stopped at Little Mountain pass to give the current sky condition one last peek with binoculars. On stopping, I saw the same, clear, cloudless sky with good seeing that Bob described. M7 (Ptolemy's cluster), M6, M8 (Lagoon) and M24 (Small Sagittarius Star Cluster) were all naked-eye objects. Milky Way light cloud regions could be seen from Sagittarius through Cepheus. Theta-Rho Oph dark lanes could not be seen - too close to SLC light pollution gradient. Sky orientiation was typical for early July with the Milky Way spinward arm at 40 degs alt to the eastern horizon. Essentially, it was like a Unita class sky for seeing and transparency, reduced in contrast by SLC light pollution. The air was cold and still - I could easily see my breath during normal breathing. Pulling out 10x50 binos I was able to quickly tick off the basic Messier summer objects: the globs M10 and M14 in Oph; M22, M24, M17 in Sagittartius; M11,the Scutum Star Cloud and M27 and the Coathanger asterism in Sge; split Alberio; M29 in Cyg; the some of the outline of NGC7000 and Harrington 14 in Cyg; M52 in Cep; the Herschel's Garnet star in Cep - which was looking particularly garent that night; and ending with splitting the cat's eye wide double Drac 16-17. Really a quite amazing half-hour. Then I drove home (20 minutes), got out of the car and looked up to find the next incoming band of mid-altitude clouds directly overhead covering 20 percent of the sky. Lesson learned: This year may be "eastern" or "midwest" style observing. The opportunities will be in the leeward side of passing cloud fronts and last an hour or two. Plan to set up, read a book for a while until a cloud band passes, the sky opens up and "magic time" begins. - Kurt _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com
I realize that ATMing is a dying practice, but home-made focal reducers aren't too difficult using surplus optics. The trick is sometimes finding just the right achromats, but pin-point stars are easily obtainable for not a lot of money. On Sun, Jun 8, 2008 at 6:47 PM, Don J. Colton <djcolton@piol.com> wrote:
Denkmeier has a .5 focal reducer made specifically for SCT's and I have had no problem using it on both an 8-inch and 14-inch Celestron SCT's with a 2" diagonal. It works great making an 8" SCT a wide field scope with pinpoint stars.
participants (3)
-
Canopus56 -
Chuck Hards -
Don J. Colton