|
|
Thread Tools | Display Modes |
#31
|
|||
|
|||
On Sun, 06 Feb 2005 11:56:59 -0500, Stephen Paul
wrote: Dan McShane wrote: Stephen Paul wrote in message Nothing like a lightweight, fast cooling solution. Of which, both the OA and the refractor are capable. If the bottom line is price/performance, the OA is likely the winner, but a refractor is generally more trouble free. If the two perform equally. Unfortunately, there's no way to know that (equal quality), without doing a direct comparison. Order them both, keep the better one. You have 30 days (last I checked). Stephen, I would fortify the opinion that only a top shelf 4" APO will give an OA-4/3.6 a run the money. Right, and so the question remains whether the Orion OA is better at the eyepiece than the Orion 100ED, and whether the buyer is one who cares more about the optical differences than the differences in design (eyepiece position, maintenance, and mount requirements come to mind). I hope that there's no one reading this who is interpreting my comments as negatively or positively favoring one design over the other as a matter of optical quality. While I do prefer the refractor for the design, I think I'm on record as backing the OA 100% as an optically excellent alternative to a long focus APO of equal aperture. The OA Pros: Excellent optical performance if will implemented. The Cons: Length of OTA and resultant eyepiece position. (Long focus Newts just don't scale well, imposing aperture limits.) -Stephen How about collimation issues? That's a con. Or light throughput compared to the refractor? -Rich |
#32
|
|||
|
|||
I too have been looking at this scope.
So, is it the consensus of the group that their performance can match a 4" APO? Has anyone done a side by side comparison? TMT |
#33
|
|||
|
|||
RichA wrote in message ... On Sun, 06 Feb 2005 11:56:59 -0500, Stephen Paul wrote: The OA Pros: Excellent optical performance if will implemented. The Cons: Length of OTA and resultant eyepiece position. (Long focus Newts just don't scale well, imposing aperture limits.) -Stephen How about collimation issues? That's a con. Not all refractors are perfect out the box. Objectives aren`t always squared to the optical axis. I would cite all the problems Meade had with their ED`s 3 or 4 years ago. Or light throughput compared to the refractor? "While the AP threw up a slightly brighter image, there was little to choose between the scopes." http://www.scopereviews.com/page1m.html#3 Which is pretty much what you could expect because the Traveller is 105mm vs. 98mm for the OA-4. And that`s vs. a high quality APO with high quality coatings (97% TX, objective only). OANs have just 2 coated surfaces with enhanced 96% coatings so you`re getting 92% TX at the focal plane. I doubt the current crop of budget APOs have nearly as good TX%, especially air spaced EDs. It is a myth that the APO has any significant, if any, advantage in throughput. Dan McShane -Rich |
#34
|
|||
|
|||
On Mon, 7 Feb 2005 21:15:42 -0500, "Dan McShane"
wrote: Hi Dan, OANs have just 2 coated surfaces with enhanced 96% coatings so you`re getting 92% TX at the focal plane. Understood and I'm sure you're using top quality coatings, but that's the coating efficiency of freshly aluminized surfaces. According to Bryan Greer (Protostar), all aluminum coatings begin losing reflectivity upon leaving the chamber, falling a few percentages after a few months. Refractors keep refracting at virtually the same transmission unless the coatings are damaged. One factor that can hold a high quality OAN back from consistantly refractor-like performance is the fact that open reflective systems are affected by thermal gradients near the optical surfaces and in the tube. Add to that the disadvantage of the primary at the bottom of the deck that must pierce periodic wafting of heat fom the observer traversing the optical path, an equal sized refractor (of any type) will, as you like to say, put the max. energy in the diffraction disk--- for a greater percentage of time---than a reflector with the primay at the bottom. Getting the objective as far off the ground and as far away from the operator as possible is an irrefutable advantage for high power viewing. Why don't you add an optical window? Think of the potential of keeping the tube quiescent and the mirrors clean and bright for years, and your next wave of SAA infomecials could cover even more ground... Dan C. |
#35
|
|||
|
|||
Dan Chaffee wrote in message ... On Mon, 7 Feb 2005 21:15:42 -0500, "Dan McShane" wrote: Hi Dan, OANs have just 2 coated surfaces with enhanced 96% coatings so you`re getting 92% TX at the focal plane. Understood and I'm sure you're using top quality coatings, but that's the coating efficiency of freshly aluminized surfaces. According to Bryan Greer (Protostar), all aluminum coatings begin losing reflectivity upon leaving the chamber, falling a few percentages after a few months. Refractors keep refracting at virtually the same transmission unless the coatings are damaged. Well let me see, just to lay down my creditials, beginning in 1984 I worked for Balzers USA, Contraves, Corion Inc, Optical Corporation of America, Corning Photonics Division up until April 2002. I`ve been involved with some of the most sophisticated technologies and thin film processes there are. At Optical Corporation of America I was involved with the development of the first ultra-narrow, ultra hard coating bandpasses which were the prototypes of filters used in fiberoptics Wavelength Division Multiplexers (WDM). And I designed my own Nebula Filters. http://users.erols.com/dgmoptics/LPRfilters.htm. So I think I can speak with a degree of authority on the subject of optical thins that very few on this or any other group can. A properly applied RX% coatings *might* lose a few 1/10ths of a percentage of RX%, NOT a few percent. Only the most poorly executed coating would lose that much RX% in such a short period. BTW, your statement regarding AR coatings used for refractors is not completely accurate in that even improperly applied hard oxide coatings are also subject TX% loss, and even some WL shift, if the coating is not dense enough and/or a non-dense film is not identified and carefully low temperature annealed. All it takes is a single layer applied during the process to compromise the film. With thin films process is everything and it applies to all optical thin films, not just RX% coatings. Why don't you add an optical window? Think of the potential of keeping the tube quiescent and the mirrors clean and bright for years, and your next wave of SAA infomecials could cover even more ground... SAA infomercials? I consider it more like countering the SAA *Office of Speculative Baseless Disinformation*. :-) Dan McShane Dan C. |
#36
|
|||
|
|||
I remember that pickture. I always wanted to build one, since, before
the advent of dobs, it looked like a good solution to getting a lightweight mount. It was a standard Newtonian, as I recall. I don't remmeber how many were actually built, but there was an article on it in an old Sky & Tel probably from the 1950's. Bill Meyers Jb2269 wrote: Dan, An interesting discussion on the construction of modern OAN's but isnt this an ancient design used at long f ratio as far back as the 1800's? I seem to remember a picture of one with a bipod set of legs at the eyepiece end so it could be proped up in one of the ATM books. Bill Bambrick 41 N, 73 W, 95 ASL |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
IMAGINOVA's ACQUISITION OF ORION | Victor | Amateur Astronomy | 1 | January 15th 05 07:42 AM |
Ted Taylor autobiography, CHANGES OF HEART | Eric Erpelding | Policy | 3 | November 14th 04 11:32 PM |
Sedna, space probes?, colonies? what's next? | TKalbfus | Policy | 265 | July 13th 04 12:00 AM |
meade ETX125 v Helios 5.1" reflector | Quaoar | Misc | 3 | November 9th 03 09:42 PM |
SCT CO and Aperture question | Roger Hamlett | Amateur Astronomy | 3 | August 8th 03 08:14 AM |