Re: [Utah-astronomy] Collimation of a Dobsonian
This discussion of collimation has been fascinating! I've owned my 10" Odyssey Dobsonian for almost 20 years, and I have never collimated it, unless I did so when I first got it (which I definitely cannot remember). Indeed, I'm sure I wouldn't know how to begin - even after reading all of these wonderful posts. If my scope is "off," I'm too much of a rank amateur to know the difference. I use my scope to look at planets, the moon, an occasional comet, and various Messier objects and easy double stars. Mostly, I use it to dazzle my family or some school, church or scout group. Since my limited knowledge is slightly greater than theirs (or my misinformation is beyond their detection) they think I'm a great astronomer - as often as not they call me an "astrologer." So, I read Chuck Hards' posting: "But if you are mainly observing deep-sky objects at low to medium powers with wide-field eyepieces, collimation can be off by a surprising amount with no noticeable effects on the imagery," and I figure I can probably go another 20 years without worrying about collimation. But then, in that same entry he said: "A fast system (say, f/4) of long effective focal length (i.e., large aperture), used for imaging at high power or planetary viewing or very close double star splitting, should be collimated very precisely," and I wonder if any of that applies to me, and if I should think about collimation. Unfortunately, I don't even know the f/ value of my scope. (It's a red tube about 4 ft. long with a 10" diameter mirror. Does that help?) I do look at planets (especially Jupiter, Saturn, Venus and Mars), but usually not with my high-power lense. I haven't noticed any difficulty in getting a crisp image by fine-tuning the focuser, so I don't know if my views would improve with collimation or not. Any advice from any of you REAL experts to an admitted rank amateur like me? To give you an idea of my lack of sophistication, when I first got my scope, I couldn't even figure out how to focus it. Patrick Wiggins took the time to patiently explain how to extend the focussing tube. Duh! Patrick, you're the greatest! Raeburn G. Kennard 12082 Joey Park Place Draper, UT 84120 (801) 321-4867 rkennard@kmclaw.com
If it's been 20 years, it's time to clean your mirrors. That's a subject unto itself, don't try it without learning about cleaning first-surface mirrors beforehand. The Odyssey telescopes can be frustrating to collimate due to the oversimplified optical supports. If you can bring it to a star-party, I'd be happy to take a look and help you tweek the collimation, if needed (and it probably does need it). We can help you clean your optics as well. On Wed, Apr 23, 2008 at 11:48 AM, Raeburn Kennard <rkennard@kmclaw.com> wrote:
This discussion of collimation has been fascinating! I've owned my 10" Odyssey Dobsonian for almost 20 years, and I have never collimated it, unless I did so when I first got it (which I definitely cannot remember). Indeed, I'm sure I wouldn't know how to begin - even after reading all of these wonderful posts.
Raeburn, I have a 10" Coulter Dob that is an even older blue tube. Your scope like mine is probably an f/4.5. When my scope is collimated well I have been able to view planets with amazing detail at 400x or more. In order to get this kind of performance I need to collimate it every time I use it. At low power 100x or so you won't notice much difference but at higher powers the difference is dramatic. Clear Skies, Don -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Raeburn Kennard Sent: Wednesday, April 23, 2008 11:49 AM To: utah-astronomy@mailman.xmission.com Subject: Re: [Utah-astronomy] Collimation of a Dobsonian This discussion of collimation has been fascinating! I've owned my 10" Odyssey Dobsonian for almost 20 years, and I have never collimated it, unless I did so when I first got it (which I definitely cannot remember). Indeed, I'm sure I wouldn't know how to begin - even after reading all of these wonderful posts. If my scope is "off," I'm too much of a rank amateur to know the difference. I use my scope to look at planets, the moon, an occasional comet, and various Messier objects and easy double stars. Mostly, I use it to dazzle my family or some school, church or scout group. Since my limited knowledge is slightly greater than theirs (or my misinformation is beyond their detection) they think I'm a great astronomer - as often as not they call me an "astrologer." So, I read Chuck Hards' posting: "But if you are mainly observing deep-sky objects at low to medium powers with wide-field eyepieces, collimation can be off by a surprising amount with no noticeable effects on the imagery," and I figure I can probably go another 20 years without worrying about collimation. But then, in that same entry he said: "A fast system (say, f/4) of long effective focal length (i.e., large aperture), used for imaging at high power or planetary viewing or very close double star splitting, should be collimated very precisely," and I wonder if any of that applies to me, and if I should think about collimation. Unfortunately, I don't even know the f/ value of my scope. (It's a red tube about 4 ft. long with a 10" diameter mirror. Does that help?) I do look at planets (especially Jupiter, Saturn, Venus and Mars), but usually not with my high-power lense. I haven't noticed any difficulty in getting a crisp image by fine-tuning the focuser, so I don't know if my views would improve with collimation or not. Any advice from any of you REAL experts to an admitted rank amateur like me? To give you an idea of my lack of sophistication, when I first got my scope, I couldn't even figure out how to focus it. Patrick Wiggins took the time to patiently explain how to extend the focussing tube. Duh! Patrick, you're the greatest! Raeburn G. Kennard 12082 Joey Park Place Draper, UT 84120 (801) 321-4867 rkennard@kmclaw.com _______________________________________________ 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
Saturday I met with Raeburn Kennard to examine his 10" Odyssey. The optics were remarkably clean for such an old telescope, so much so that a cleaning wasn't warranted. He is to be commended for taking such care to protect his optics. Also his collimation was so close that it came down to the utilitarian sink-trap focuser being the sole reason for any out-of-collimation condition. Again, remarkable to see a cardboard Dobsonian hold collimation so well, for so many years. Upgrading to a new, more precise focuser was discussed as an option. Many veteran observers could take a lesson from the meticulous care Raeburn has obviously exercised with this telescope. The optical tube is essentially in new condition, even though he has used it extensively over the years.
This reminds me of a question I've been meaning to ask some of you experts. What seems like a simple solution to dust on primary mirrors -- a piece of saran wrap gently laid over the primary to act as a dust barrier when stored, I've been told is a really bad idea, as there is some kind of out-gassing of plastic compounds that interacts with the mirror surface, etc. Is this in fact true, and if so, it seems to me that some enterprising chemist could come up with the equivalent "plastic wrap" that would not have such a problem. Or is the problem something else (e.g., risk of scratching, etc.)? --- Chuck Hards <chuck.hards@gmail.com> wrote:
Saturday I met with Raeburn Kennard to examine his 10" Odyssey. The optics were remarkably clean for such an old telescope, so much so that a cleaning wasn't warranted. He is to be commended for taking such care to protect his optics. Also his collimation was so close that it came down to the utilitarian sink-trap focuser being the sole reason for any out-of-collimation condition. Again, remarkable to see a cardboard Dobsonian hold collimation so well, for so many years. Upgrading to a new, more precise focuser was discussed as an option.
Many veteran observers could take a lesson from the meticulous care Raeburn has obviously exercised with this telescope. The optical tube is essentially in new condition, even though he has used it extensively over the years. _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com
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Years ago my 10" Parks mirror came packaged just as you described, with plastic wrap directly adhered to the aluminum surface. So, thinking that Parks wouldn't do anything to their mirror that would cause problems, I also stored it that way. Bad idea. My mirror has permanent marks on it, whether from out-gassing or some other process I couldn't say. The marks look a bit like streaks left from Windex. As near as I can tell the performance has never been compromised, but I am sorry that I marred the surface. BTW, the Parks mirror has been a fabulous investment - well-figured, very sharp images (even at high power) and a joy to use. Kim -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Richard Tenney Sent: Monday, May 05, 2008 12:13 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Collimation of a Dobsonian This reminds me of a question I've been meaning to ask some of you experts. What seems like a simple solution to dust on primary mirrors -- a piece of saran wrap gently laid over the primary to act as a dust barrier when stored, I've been told is a really bad idea, as there is some kind of out-gassing of plastic compounds that interacts with the mirror surface, etc. Is this in fact true, and if so, it seems to me that some enterprising chemist could come up with the equivalent "plastic wrap" that would not have such a problem. Or is the problem something else (e.g., risk of scratching, etc.)? --- Chuck Hards <chuck.hards@gmail.com> wrote:
Saturday I met with Raeburn Kennard to examine his 10" Odyssey. The optics were remarkably clean for such an old telescope, so much so that a cleaning wasn't warranted. He is to be commended for taking such care to protect his optics. Also his collimation was so close that it came down to the utilitarian sink-trap focuser being the sole reason for any out-of-collimation condition. Again, remarkable to see a cardboard Dobsonian hold collimation so well, for so many years. Upgrading to a new, more precise focuser was discussed as an option.
Many veteran observers could take a lesson from the meticulous care Raeburn has obviously exercised with this telescope. The optical tube is essentially in new condition, even though he has used it extensively over the years. _______________________________________________ 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
____________________________________________________________________________ ________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ _______________________________________________ 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 ______________________________________________________________________ This e-mail has been scanned by Cut.Net Managed Email Content Service, using Skeptic(tm) technology powered by MessageLabs. For more information on Cut.Nets Content Service, visit http://www.cut.net ______________________________________________________________________ No virus found in this incoming message. Checked by AVG. Version: 7.5.524 / Virus Database: 269.23.8/1415 - Release Date: 5/5/2008 6:01 AM No virus found in this outgoing message. Checked by AVG. Version: 7.5.524 / Virus Database: 269.23.8/1415 - Release Date: 5/5/2008 6:01 AM
Yes, bad idea. Besides contact abrasion, moisture gets trapped beneath the film. I've had excellent results with just making sure the tube assembly is capped on both ends, and the focuser. Then, and here's an important detail, store the tube horizontally, so the mirror surface is vertical. Dust is less prone to settling on a vertical surface. Some people prefer a "contact" mirror cover. In that case, use a breathable, soft material such as felt. It will actually only contact the mirror on the edges unless the f-ratio is very slow, but there is still the probable risk of scratches due to abrasion. I'm surely no expert, but 4+ decades of experience has taught me many lessons. It's an unfortunate fact of life that the people in the shipping department of some optical companies are not highly-paid expert technicians! On Mon, May 5, 2008 at 1:38 PM, Kim <kimharch@cut.net> wrote:
Years ago my 10" Parks mirror came packaged just as you described, with plastic wrap directly adhered to the aluminum surface. So, thinking that Parks wouldn't do anything to their mirror that would cause problems, I also stored it that way. Bad idea. My mirror has permanent marks on it, whether from out-gassing or some other process I couldn't say. The marks look a bit like streaks left from Windex. As near as I can tell the performance has never been compromised, but I am sorry that I marred the surface. BTW, the Parks mirror has been a fabulous investment - well-figured, very sharp images (even at high power) and a joy to use.
participants (5)
-
Chuck Hards -
Don J. Colton -
Kim -
Raeburn Kennard -
Richard Tenney