Posts Made By: Rod Kaufman

Finally got the scope out last night in front of my home and despite the fact that I've got moderate light pollution and a crescent moon up till midnight, the scope performed beautifully. Under the aforementioned conditions with decent transparency and seeing, and while it just many be my personal bias entering into it, the images equaled or perhaps exceeded my expectations. I hit the major constellations around the zenith and that means Canes Venatici and Coma Berenices and that means galaxies and lots of them! For the best views under my observing conditions, I used a 17mm type four nagler with a CLS filter. I find this focal length works optimally with my filter and it wrings out detail that otherwise might be invisible under my skies. First up, M51, with detail in the structure that also held up well with a 10mm Ethos eyepiece. I hit six more messier/NGC galaxies in CV including the whale and the pup and the hockey stick. And no, I didn't forget M3 either! In Coma, M98 and M99 are a real treat along with NGC 4565 M88, M91(aka missing the messier) NGC 4725, M64, and the globular cluster, M53.  Although more into the light pollution for my locale I spent some time with the sombrero in Virgo and M81/82 in Ursa Major. 
I rounded out the evening with a detailed viewing of Jupiter with numerous intricacies in the belts and bands in a 9mm ES 100 AFOV and a paracor. 
I chose to replace my astrosystems/Discovery(same maker) 3.1" secondary because its coating was a bit weatherbeaten and since neither alcoat or majestic offer an enhanced aluminum coating and the other local boys are pretty much dog nuts on their prices for an enhanced recoat, I went with a new high end secondary from antares optical, see link in my initial post in this thread, and that comes with a highly enhanced coating along with interferometry data. 
If memory serves, I recall Roland Christian posting about a serious observer who frequently recoated his mirrors and claimed to discern a noticeable difference in performance. That was my impression last night and my optics have previously held their own and then some up against similar apertures under dark skies. In fact, Roland's statement about my primary mirror data on a real and not a synthetic interferometry report as posted on the Astromart years ago was, "quite nice mirror actually". 
I think it's optimal now with a new coating from alcoat...

Keith,
I noticed in your user profile that you have the means to test optics. I read one of the reviews on the alcoat site by an ATM who did just that and found pre and post coating values to be virtually identical. It would be interesting if you might consider doing the same. I found my optic to be delivering optimum performance after the recoat so I'm delighted with alcoat's service and I believe your experience with it would be of value to the general readership of the forum. 
Hope to read more from you...

Originally Posted by Keith Lawson

All,

Just got the mirror back from Alcoat. Quick turnaround. Looks real good Bob even refunded me my overpayment of $0.10! I have a new secondary that should arrive today. Time to get this old Cave back under the stars!

Keith (Scopejunkie)

Keith,
Glad you've got your mirror back and Alcoat's got a good turnaround time. 
Any chance you can place your mirror on an optical bench and check the smoothness of its surface post recoat?

Keith,
Good luck on the tests and your seeing conditions. Last night, Saturday 6-2, was one of the best in front of my home that I've ever seen. The transparency was incredible, thanks to a high pressure dome over SoCal. The seeing was poor early on and then firmed up enough to allow splendid views of galaxies. I could even see the milky way in Cygnus as it was rising up but well shy of the zenith. I was astounded on how much detail I could see in many galaxies as I viewed them in my 16" scope with an ES 14mm 100 AFOV eyepiece/paracor/CLS filter combo. It was just a great night and I observed until the moon rose over the horizon. I'm still jazzed about it!

Keith,
Looking forward to your reply on the performance of your scope, post recoat. 
I checked the clear sky clock for your locale on Sunday evening, 6-3, and it doesn't look too good with winds in the area.
I'm drooling over the clear sky clock prediction for Sunday evening, 6-3, at Mt Pinos with excellent seeing and transparency in the forecast with no wind. The latter is only an hour north from me but I've got a heavy day at work on Monday so it'll have to wait. Nevertheless, I'm still delighted over my observing session in front of my own home last night and I'm within the 10 mile observing radius of the clear sky clock prediction for Templin Highway so I'll keep an eye on that one.
Clear, dark and steady skies...

I generally have my 16" mirror recoated at ten year intervals but I decided to do it two years earlier than planned for various reasons. I selected alcoat to do my recoat for several reasons. First, it's relatively close to me in that I'm in Socal and alcoat is in Nocal so I didn't have to ship my mirror very far and the cost to do so is significantly less than shipping out of state or to the east coast where another popular coater called majestic is located. Both the latter and alcoat are reportedly one man operations wherein the work is done in a garage with a standard aluminum coat and quartz overcoat applied by the vendor. Alcoat is significantly less expensive than any other coater and at total initial cost of $135.00 including shipping, there's no comparo in terms of cost, period. Notice I stated "initial cost" because alcoat refunded me an additional twelve bucks and change that I didn't know I had coming to me because the shipping cost was actually less than anticipated. In other words, you're dealing with an honest gentleman. 
Turnaround time was a reasonable week and a half for decoat and recoat. The new coating looks beautiful as they usually do and I'll hopefully have first light with it soon.
I upgraded my secondary from an older but serviceable 3.1" discovery elliptical mirror to the high end antares optical secondary mirror from their website:
http://www.antaresoptics.com/
Check out alcoat here:
http://www.alcoat.net/
along with an image of the veteran coater Bob Fies of alcoat pictured with John Dobson when Dobson was still with us:
http://www.alcoat.net/al_4-00.htm
Hopefully Bob Fies will be coating mirrors for many years to come and I'm glad I had him service my mirror.

Tom,
I personally wouldn't want a 6" F12 due to the size of the supporting structure although you could leave the mirror spherical without the need to parabolize it and still have a primary at better than a quarter of a wave at that f-ratio. I wouldn't want to have an f-5 16" either due to the longer structure when an f4.5 like mine would do just as well. Unless you want to have a labor of love, I'd buy a GSO mirror from Agena astro at around 1200.00 and probably do well with it, similar to these tested by interferometry:
http://r2.astro-foren.com/index.php/de/11-beitraege/03-newton-systeme-und-verwandte-fragen/260-c065-zwei-gso-16-zoeller-f4dot5-im-vergleichgso
Then I'd put a cover over the mirror with a round hole in it about 5 or 6 inches in diameter, similar to a trap door installed on my astrosystems mirror cover, and open it for an unobstructed 6" f11 system or so, if I wanted that particular aperture along with the 16" primary without the cover. I think that's a better way to go...

It's amazing what somebody can cobble together that works and is dirt cheap:
First, the interferometer:
http://www.instructables.com/id/CHEAP-INTERFEROMETER-FOR-OPTICAL-TESTING-OF-TELESC/
Then, a 22" dob structure:
http://www.instructables.com/id/Making-22-Inches-Dobsonian-Telescope-Body-Under-10/
I bet that dob structure works a lot better than the stuff they sell to us...

While I don't own an ES 12" F5 dob, I did spend some time viewing thru one in a dark sky location. Before I begin my review, I do like to search the net for optical tests that may have been performed on similar units. I did find an example of another 12" F5 ES mirror tested with interferometry and that particular sample didn't fare very well at all:
http://www.astroreflect.com/images/pictures/tests_out/mirror3.png
Nevertheless, I had access to a model and I decided to put it thru its paces. The owner took awhile to put it together and and perhaps that was due to his unfamiliarity with it but it seemed it just took a lot longer than it should. In comparison, I probably could have assembled and disassembled my 16" astrosystems truss dob a couple of times over by the time the guy had it up and running. Although collimating the scope is relatively easy since you do it from the front of the scope versus the rear, this isn't really an innovation and Stephan Collet Phd of Bakersfield California had perfected a similar system years ago. I'm partial to the more traditional rear to front collimation procedure but either will work quite well so that's a matter of personal preference. 
While a shroud wasn't necessary under dark skies, you'd want to have one if neighbor's lights are a problem, and I feel it should be supplied with the scope instead being an option. But that's an issue you see with a lot of new scopes these days. 
Balance is a potential issue as well and I'd recommend an optional counterweight accessory, especially if you frequently change heavy two inch eyepieces in the focuser like I do. That's a problem in many scopes, though.  In contrast, the sticktion in my astrosystems dob allows me to changes eyepieces at virtually any useable angle without any counterweight necessary and that's a real convenience that I've come to take for granted. My previous Discovery 12.5?" truss dob had a similar balance problem with heavy eyepieces and that proved to be a pain in the butt, especially in cold weather environments. 
Movement of the ES 12" truss dob was well-controlled overall and the unit seemed to have a heavier substantial feel to it and I liked it better than my previous 12.5" Discovery truss dob. The design of the ES model is quite good in comparison to similar sized scopes that I have used in the past. 
The focuser works well and it, too, has a quality feel to it. I don't believe you'll find a real need to replace it. 
Observing comfort, even at the zenith, is very good and motions around "Dobson's hole" are well controlled.
There appears to be a paucity of DSC systems available for these models at this time and I personally consider that to be a significant drawback but that, too, is an individual preference.
Now to the optical performance of the unit in question. My particular sample worked very well. It thru up a bright, contrasty image of the Cat's Eye nebula under high magnification. Globular clusters were well resolved and similar in appearance to that of a more expensive premium style scope. The star test didn't reveal any glaring errors but just a bit of under-correction. I didn't see any astigmatism, either. So both the primary and secondary were likely ok in this sample. Unfortunately, the planets weren't well-placed for observation so I can't comment about it with this scope.
I must say I liked the scope very much but this is, of course, a sample of one so take that into consideration when considering the purchase of a production scope...

Scroll down to bottom page in link:
http://www.scopereviews.com/page1ap.html#1
Skywatcher is a good one that won't break the bank...