Click here if you are having trouble logging into the forums
Privacy Policy |
Please read our Terms
of Service | Signup and
Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
starrancher
professor emeritus
Reged: 06/09/09
Posts: 620
Loc: Northern Arizona
|
|
I'm more of a "classical" type guy . "Refractors & Newts" . But that 9.25 is supposed to have the best of optical quality in the SCT .
--------------------
LXD75 AR5
LXD75 SN8
Series 4000 Plossls
Misc. other stuff
Fort Rock , Az .
|
wfj
sage
Reged: 01/10/08
Posts: 260
Loc: California, Santa Cruz County
|
|
Quote:
=> You have already looked  through one of those Tak TSA-120s???!
Wonderful, so you were one of the first! - Please tell the rest of that story: What have you seen? 
Chris
One of the virtues of having Japanese business contacts ...
especially if you've appreciated the 102 before.
And especially if you are being lobbied to rejoin the fold. "The quality goes in before the name goes on".
I'm no reviewer, and one evening in Tokyo doesn't constitute representative performance - was I seeing a final product?
Plus one of the downsides of Japanese business contacts is to be subdued on sensitive matters like new product introductions. Otherwise ... but do you really doubt the firm in the slightest here?
|
Jared
Carpal Tunnel
Reged: 10/11/05
Posts: 2540
Loc: Piedmont, California, U.S.
|
|
By my calculations, and assuming typical Strehl ratios for each optic (I chose 87% for the Newt and 92% for the refractor--sample variations could be significantly better or worse) the Newt would have the following advantages:- 23% additional brightness (after accounting for light loss from scatter and the central obstruction)
- Very slightly better planetary performance under the absolute best circumstances--fully cooled, perfect collimation, seeing conditions of 1.8 arc seconds or better
- Free (since you already own it)
The ED refractor would have the following advantages:- Easier to mount on a GEM (if planets are your primary interest) for tracking
- No collimation required
- Faster cooling
- No diffraction spikes on planets
- Less susceptibility to tube currents
- Likely a nicer fit and finish
In my opinion, the benefits of the refractor are likely to outweigh the benefits of the reflector under all but the very best conditions, and even under ideal circumstances the performance between the two should be awfully close. If you can afford it, I'd go ahead and trade up to the refractor. It's one of those situations where you would be moving from a scope you need to worry about--is it fully cooled? Did I collimate it properly? Could it benefit from just a bit more tweaking?--to a scope that just gets out of the way and lets you observe. Go for it.
--------------------
- Jared Willson
- TMB 152 f/8 Apochromat
- Fluorostar FLT-110 w/ TEC optics
- Stellarvue SV80S
- Astro-Physics Mach1 GTO
- Takahashi Teegul SP Mount
- STL-11000
|
RAKing
Carpal Tunnel
Reged: 12/28/07
Posts: 2092
Loc: West of the D.C. Nebula
|
|
Quote:
How do you think a C9.25 would do against a 127mm APO??
I own both - a C925 carbon fiber SCT and a Tak FS-128. But since this is off topic, I'll just say they both work great. I also have a nice little 8 inch Newt and the Tak works better for me. 
I understand Ed's reasoning and value his opinion very much, but I still feel a 120mm would do a great job for the OP and I would be bugging some dealer about when I could get the new TSA-120. YMMV. 
Ron
--------------------
Time spent looking at the stars is added to your life.
Tak FS-128, C925-CF, C6SE, other stray cats and refractors.
A-P Mach1 GTO
Zeiss orthos to Ethos - and some stuff in between.
|
Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2704
|
|
On paper, I would give the C9 the upper hand. The extra aperture is highly obstructed robbing a lot of contrast, but there is a lot of aperture there as well. Even if the optics are not perfect, it should not do WORSE than the 127mm.
Ah, but the quality is the big variable. I owned a C9 about 9 years ago and that sample had perhaps the poorest optics on any SCT I have ever owned. I would have been afraid to match it up to a good 4" APO.
But that scope was a (I hope) rare exceptoin.
The other benefit of the extra aperture is that even if the contrast is not much better, you will find that the color saturation will be greatly improved in the larger scope. Mars will look redder, Saturn will look yellower and show more smokey detail in the clouds, and color detail on Jupiter will be much improved. This aspect is often overlooked in the small refractor vs large reflector comparisons, but it is one of the MAIN differences I can see when comparing say a 6" APO to a C14 (as an example). I see much richer color in the C14.
I know it seems unfair, but I often hear how much better smaller scopes are when the seeing is less than perfect, and I don't find that to be true. Last week I was out and had my C14 and my TV 101 out at the same time. Seeing was not great, but at 97x on the C14, I could see a sharper and more detailed view than at 140x in the refractor. Part of this was simply due to the fact that the belts and cloud bands not only have shapes and subtle details, they also have colors that differ greatly in tone. The C14 could show these color graduations very distintly. In the 4", all of the colors were rather drab.
I would expect the same in a C9 vs 5" APO comparison. I noted this difference when comaparing my C11 to my Meade 152ED. Often it was hard to perceive more detail in the C11, but the color saturation always seemed better in the C11. Even when seeing kept either scope from showing fine deatil, you still get the benefit of the richer colors in the larger scope.
--------------------
Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
|
stevew
Pooh-Bah
Reged: 03/03/06
Posts: 1148
Loc: Vancouver
|
|
Quote:
a 120mm-ED which, by the way, can not be called a true Apo if it's not a triplet,
Huh?.... It has to be a triplet to be considered an apochromat?
Does that go for the Tak FS line, or the TV102 as well?
--------------------
TV Genesis SDF
Meade 127ED
Antares 152
Celestron C5
Celestron C8
Celestron C11
Coulter Odyssey 8
16 Dobsonian
|
roadi
professor emeritus
Reged: 08/18/07
Posts: 531
Loc: Denmark
|
|
Quote:
By my calculations, and assuming typical Strehl ratios for each optic (I chose 87% for the Newt and 92% for the refractor--sample variations could be significantly better or worse) the Newt would have the following advantages:- 23% additional brightness (after accounting for light loss from scatter and the central obstruction)
- Very slightly better planetary performance under the absolute best circumstances--fully cooled, perfect collimation, seeing conditions of 1.8 arc seconds or better
- Free (since you already own it)
The ED refractor would have the following advantages:- Easier to mount on a GEM (if planets are your primary interest) for tracking
- No collimation required
- Faster cooling
- No diffraction spikes on planets
- Less susceptibility to tube currents
- Likely a nicer fit and finish
In my opinion, the benefits of the refractor are likely to outweigh the benefits of the reflector under all but the very best conditions, and even under ideal circumstances the performance between the two should be awfully close. If you can afford it, I'd go ahead and trade up to the refractor. It's one of those situations where you would be moving from a scope you need to worry about--is it fully cooled? Did I collimate it properly? Could it benefit from just a bit more tweaking?--to a scope that just gets out of the way and lets you observe. Go for it.
Not trying to talk the OP from buying a refractor  but my math says the reflector has a light throughput of at least 33% in advance over the refractor assuming 89% refl of the mirror and 0.5 mm spidervanes and a 1" CO.
At f8 collimation will be a simple matter and the 6" reflector is probably lighter than the 120ED.
If the optics of the refl. has a strehl .87 it'l beat the 120ED on planetary performance in modest seeing conditions too and go deeper on dimmer objects. Laws of physics.  The refl will likely cool down a bit faster than the ED120.
Since the OP already have the 6" refl and it probably wont bring him much cash by selling, why not keep it and buy the ED120 and compare?
--------------------
Regards Rodi
60mm Polarex, Sky90, µ210, SKW150 Binoscope
Vixen GpDx, Astro5, LX200
Modified Baader/Celestron Binoviewer.
Panoptics, Tak LE's, Baader Ortho's, Antares Erfle's
Couple of diagonals..
|
Fomalhaut
sage
Reged: 08/16/08
Posts: 244
Loc: Switzerland
|
|
Quote:
Quote:
a 120mm-ED which, by the way, can not be called a true Apo if it's not a triplet,
Huh?.... It has to be a triplet to be considered an apochromat?
Does that go for the Tak FS line, or the TV102 as well?
Go back to my original post and you'll see that I spoke of ED-doublets, and not of Fluorite-doublets.
Plus: Even Fluorite doublets, such as the FS-series, though having the best chromatic correction of all the doublets, were not true apochromats (in the sense of having three color crossings within the visible part of the spectrum).
While today Triplet-Apos can be made of the same quality with FPL53 as formerly with Fluorite crystal, the same had never been quite possible with doublets, because it was more difficult to find a very good single partner-glass for an ED-doublet (even for FPL53) than for fluorite crystal.
As for the question of quality as mentioned by Eddgie: I would certainly not prefer ANY of the (partially Chinese made) 110 - 127 mm "Apos"  over a first class, optimized 6-inch Newtonian. But as for an excellent one, such as the TSA-120 (based on everybody's experiences with its predecessor TSA-102), I would not hesitate for a second and there would be but a yawning gap at the place in the show-room where the TSA-120 had peacefully dreamt of the stars before...
(And believe me: Based on my own experiences I'm fully aware that a good Newtonian is superior to most other, more sophisticated and more expensive designs.)
Chris
Edited by Fomalhaut (11/03/09 06:04 PM)
|
Patrick
Postmaster
Reged: 05/16/03
Posts: 7811
Loc: Franklin, Ohio
|
|
I don't think you will see a lot of difference between the two scopes. I suspect the contrast differences will be slight due to the reflector's larger aperture and small secondary size, and the light grasp for viewing DSO's will be better.
The length of the 6" f/8 is approx 48" while the 120ED is close to 40" once you add the diagonal and dew shield, so there's not much difference there. A 6" f/8 Newtonian is small enough to mount on a CG5 class mount if you want tracking.
If you're planning on imaging, then the refractor makes more sense, otherwise I'd put the $1500 towards a good mount and a set of collimation tools.
Patrick
--------------------
10" f/6 Truss Tube Newtonian
Celestron C6S-GT SCT
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
Celestron Regal 8x42 Binocular
Canon XSi; Meade DSI;SPC900-NC
Vixen GP2 Photo Guider Mount
My Astronomy Pages
|
Patricko
Carpal Tunnel
Reged: 01/30/07
Posts: 1534
Loc: SE New Mexico USA
|
|
I'm with Patrick on this one, not enough of a difference to bother with getting a 120ED. Keep the cash unless you want to do imaging. 
--------------------
Clear skies,
Patrick
INTERNATIONAL DARK SKY ASSOCIATION
60MM TELESCOPE CLUB!
"You can always have better, but will you ever be happy with what you have?" - Me, myself, and I
|
PJ Anway
Pooh-Bah
Reged: 06/04/03
Posts: 1142
Loc: Michigan's U.P.
|
|
Quote:
I personally would not hesitate to choose, say a Tak TSA-120 (ED-triplet) over any 6-inch Newtonian in the world!
Chris
What if the 6" Newtonian was a Tak? 
--------------------
PJ
_________________
Lookum Observatory
|
Wilsonman
Pooh-Bah
Reged: 01/30/07
Posts: 1088
Loc: S.E. PA
|
|
Just my very personal opinion: I would ALWAYS prefer a high quality 4-5" refractor over a 6" reflector. I've seen a lot of 6" Newtonians over the years and I feel they do not match the refractor in overall viewing enjoyment. I believe that if you want to complement a good refractor in the 4-5" range with a reflector- you need at least an 8"- preferably a 10 or 12", if you want to see an appreciably greater amount of deep-sky detail.
--------------------
Orion X10 Intelliscope
Selsi 7X50 binocs
|
mathteacher
Carpal Tunnel
Reged: 05/13/07
Posts: 2060
Loc: SF Bay Area
|
|
Thanks, Wilsonman. I agree 100%. For some of us, there is just something special about a refractor. And yes, it goes beyond the laws of physics.
--------------------
Regards, Mr. Wang . . . . . . . My gallery . . . . . . . I'm a refractor guy!
CR 150-HD - The Hammer, Vixen ED100sf - The Skipper, Orion ST80 - The Pug, Orion 7x50 Scenix
Meade DSI Color, Vixen Porta Mount, Vixen Super Polaris, 2" pipe mount
Please join the International Dark Sky Association
|
Patrick
Postmaster
Reged: 05/16/03
Posts: 7811
Loc: Franklin, Ohio
|
|
Quote:
I believe that if you want to complement a good refractor in the 4-5" range with a reflector- you need at least an 8"- preferably a 10 or 12", if you want to see an appreciably greater amount of deep-sky detail.
Very true, but the OP is thinking about replacing his 6" f/8 Newtonian with a 120mm refractor, not complimenting it.
The biggest complaint I've had with the common variety 6" f/8 Newtonian is the focuser. However, that can be remedied pretty easily with an upgrade. If the mirror is not quite up to snuff, it can be refigured or replaced with a premium mirror, too. All totaled it would still be a lot less money than a 120ED.
Don't get me wrong though...I'd love to have a 120ED refractor. There are lots of reasons that refractors are nice, however, in this comparison, I don't think superior views are necessarily one of them.
Regards,
Patrick
--------------------
10" f/6 Truss Tube Newtonian
Celestron C6S-GT SCT
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
Celestron Regal 8x42 Binocular
Canon XSi; Meade DSI;SPC900-NC
Vixen GP2 Photo Guider Mount
My Astronomy Pages
|
Patrick
Postmaster
Reged: 05/16/03
Posts: 7811
Loc: Franklin, Ohio
|
|
Quote:
Thanks, Wilsonman. I agree 100%. For some of us, there is just something special about a refractor. And yes, it goes beyond the laws of physics.
 Yes...this is the refractor forum...I forgot, we don't have to obey the laws of physics here!
Patrick
--------------------
10" f/6 Truss Tube Newtonian
Celestron C6S-GT SCT
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
Celestron Regal 8x42 Binocular
Canon XSi; Meade DSI;SPC900-NC
Vixen GP2 Photo Guider Mount
My Astronomy Pages
|
drshr
professor emeritus
Reged: 06/09/08
Posts: 675
Loc: Darwin, Australia
|
|
I think the main problem with Newtonians IS those laws of physics. Below a certain aperture size those laws severely compromise their use. Similarly, the laws of physics go against refractors above a certain size.
IMO 8" to 10" is the threshold, above and below which the two designs show their respective strengths.
To answer the OP's question, for me a 6" Newt is just too much fiddle for the aperture. Contrast loss and spikes seal its fate.
I would sell it for what I could (not very much I fear) and buy the 120ED.
--------------------
Doc
14" F5 DOB.
APM 8" F6 Achro.
APM 105mm F6.2 CF APO.
120/F8.3
150/F5
80/F6.25ED
25x100 Binos.
To affect the quality of the day, that is the highest of arts.
|
Fomalhaut
sage
Reged: 08/16/08
Posts: 244
Loc: Switzerland
|
|
Quote:
Just my very personal opinion: I would ALWAYS prefer a high quality 4-5" refractor over a 6" reflector. I've seen a lot of 6" Newtonians over the years and I feel they do not match the refractor in overall viewing enjoyment. I believe that if you want to complement a good refractor in the 4-5" range with a reflector- you need at least an 8"- preferably a 10 or 12", if you want to see an appreciably greater amount of deep-sky detail.
I've personally even preferred a (true!) 4-inch-Apo over an 8-inch SCT (which after 17 years of use I sold in 1992 and which I have replaced by a Mewlon-180 not before this spring 2009).
I must admit I'm the kind of person who has always preferred quality (widefield, contrast, pinpoint sharpness and beauty => joy!) over quantity (brightness of everything - background included  in a limited FOV).
I have to admit my skies are NELM 5.5 to 6.5...
And of course, I accept that anybody's mileage varies...
--------------------
Currently:
Tak FS-60c (guidescope for:)
Tak FCT-100/640 on Tak EM-10
Tak Mewlon-180 on same
IntesMicro-M500
Zeiss 7X42-T*P-Dialyt + Nikon 18x70 Binoculars
Coronado Maxscope 40
Edited by Fomalhaut (11/04/09 07:09 AM)
|
jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 4076
Loc: S. Philadelphia, PA
|
|
Quote:
The refl will likely cool down a bit faster than the ED120.
Not even close. The 120ED doublet's cool down time is negligible. My 6" take a half-hour to cool completely and seldom can keep up at this time of year. That's the essential benefit of the 120ED. If your viewing sessions are short (under an hour set-up to tear-town), you'll get more out of your time with the 120ED, especially at higher mags. - j
--------------------
Fight indignorance!
The Green Goblin - 12" of dobsonian excellence!
The PortaBowl-a $100 4.5" f/8 ball-scope YOU can build!
Eero2-a 6" f/5 ball-scope you probably can't. 
|
Gord
professor emeritus
Reged: 01/06/04
Posts: 694
Loc: Toronto, ON, Canada
|
|
I know this is the refractors forum, but it's interesting how money doesn't even seem to be a consideration in most peoples responses, at least when talking about going the 120ED route.
Spend $1500 on the existing 6" newt and see what you come out with. You better have the best 120mm refractor on the planet, 'cuz that's what it's gonna take to even keep up. I'm not even so sure it could do that.
Heck, for well under $1000, that reflector is going to be crazy good. I've done it twice now, and as much as I love my 80ED and all the other very high end refractors I've had the chance to use, when you start comparing apples to apples, the big advantages that keep getting brought up for refractors don't seem to exist.
Spend a few hunderd on upgrading the optics and focuser on the 6", and then get a nice mount for it to ride on. The resulting package will stomp all over the 120ED performance wise.
And one final thought, there is no perfect scope. They all have issues. There is no free lunch. You will find advantages in the 120ED, and your reflector. It's all a matter of prioritizing what do you want most.
Clear skies,
-Gord
--------------------
* Celestron C10/Normand Fullum primary
* Tasco 11TR/Normand Fullum primary
* Orion StarBlast
* Orion Apex 102
* SkyWatcher 80ED
* Celestron CG5a mount
* MallinCam Pro & Color II
* Lots of other astro toys
...and the best wife I could ever dream of for letting it all happen!
--------------------
|
roadi
professor emeritus
Reged: 08/18/07
Posts: 531
Loc: Denmark
|
|
Quote:
Quote:
The refl will likely cool down a bit faster than the ED120.
Not even close. The 120ED doublet's cool down time is negligible. My 6" take a half-hour to cool completely and seldom can keep up at this time of year. That's the essential benefit of the 120ED. If your viewing sessions are short (under an hour set-up to tear-town), you'll get more out of your time with the 120ED, especially at higher mags. - j
I can tell for sure its close I know what I've seen no matter what you've read! and regarding cooldown time its close too, with equal in performance at least probably a slight edge to the reflector on planetary resolution and contrast, assumed same quallity of optics or just about the same and build to the right specs.
Difraction spikes are negligible when correct build/designed as with the 1" CO. I can tell from your post that you've never looked through such an instrument but just asuming an avarage budget reflector. By the way I'm a refractor guy my self but facts are facts.. also stating that cooldown time for an ED120 is negligible may be true in your area, but not so in many others.
All the refractors I've owned needed time to aclimate even in summer were I live.
And recommending a person to sell his scope/reflector no matter how cheap, is IMO an incompetent, and selfish advice so why not keep it and evt. compare?
--------------------
Regards Rodi
60mm Polarex, Sky90, µ210, SKW150 Binoscope
Vixen GpDx, Astro5, LX200
Modified Baader/Celestron Binoviewer.
Panoptics, Tak LE's, Baader Ortho's, Antares Erfle's
Couple of diagonals..
|
|
12 registered and 17 anonymous users are browsing this forum.
Moderator: desertstars, Remy Bosio, Jason B, LLEEGE
Print Thread
|
Forum Permissions
You cannot start new topics
You cannot reply to topics
HTML is disabled
UBBCode is enabled
|
Thread views: 1327
|
|
|
|
|
|
|
Previous
Index
Next
Threaded
[Re: 
Edit
Reply
Quote
