meteorite
Vendor (meteorites)
Reged: 01/28/06
Posts: 268
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Hello Everyone,
I currently use a very nice 6 inch f/8 reflector for lunar and planetary observing. It is also a great scope for double stars and the brighter DSO objects. I really like this scope, for various reasons.
I have been considering purchasing a 120 mm Skywatcher ED, refractor to basically replace my 6 inch reflector. For only $1500.00, the Skywatcher comes with an RACI finder, rings, 2 inch crayford focuser and dovetail (as well as two eyepieces). This is a really good deal, IMHO.
I am thinking the refractor would give nice contrast with very pinpoint stars (which is what I like)
I would appreciate opinions on whether the refractor would provide a more pleasing view via for example, better resolution, quicker cooldown time, more contrast than the reflector, etc.
I realize only I can decide if the refractor is right for me; just seeking others opinions. Concerning my viewing habits, I place quality of views over quantity. For me aperture does not always rule. I am not interested in AP, just visual.
I also realize I am asking this in teh Refractor forum so opinions may be somewhat biased 
Thanks everyone.
-Wal
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watcher
sage
Reged: 11/21/07
Posts: 406
Loc: NJ
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Personally,I wouldn't hesitate. I was a one scope man from 1987 until 3 years ago. I had a Celestron super C8 of average optical quality. It fell into disrepair a couple years before I got back into the hobby, so my comparison isn't a side by side,but the 120mm achro I got gives up very little if anything to the 8" for planetary and lunar. The rest of the sky is purely the domain of the refractor. The views are really something that the SCT was incapable of. I have to believe that going from a 6" reflector to a 120ED would be even more rewarding. To top it all off, you'll finally be looking into the right end of the telescope!
Joe
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(quote)"That does it! Next Big Bang, someone has got to rethink this gettin' old business!" Joe Daugert
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1986 Celestron c-8 (retired)
Celestron Omni XLT 120
Celestron Astromaster 70 AZ
Vixen GP2 mount on Omni XLT tripod (soon to be driven by iOptron GOTO Nova)
Meade 16x50 binoculars
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DLB242
professor emeritus
Reged: 07/29/08
Posts: 545
Loc: Pen Argyl, PA
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Quote:
Hello Everyone,
I currently use a very nice 6 inch f/8 reflector for lunar and planetary observing. It is also a great scope for double stars and the brighter DSO objects. I really like this scope, for various reasons.
I have been considering purchasing a 120 mm Skywatcher ED, refractor to basically replace my 6 inch reflector. For only $1500.00, the Skywatcher comes with an RACI finder, rings, 2 inch crayford focuser and dovetail (as well as two eyepieces). This is a really good deal, IMHO.
I am thinking the refractor would give nice contrast with very pinpoint stars (which is what I like)
I would appreciate opinions on whether the refractor would provide a more pleasing view via for example, better resolution, quicker cooldown time, more contrast than the reflector, etc.
I realize only I can decide if the refractor is right for me; just seeking others opinions. Concerning my viewing habits, I place quality of views over quantity. For me aperture does not always rule. I am not interested in AP, just visual.
I also realize I am asking this in teh Refractor forum so opinions may be somewhat biased
Thanks everyone.
-Wal
The What kind of mount do you have for the 6" f/8 Reflector?
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David B
10" f/5 DOB
6" f/8 DOB
Celestron C8
Antares 1529 6" f/6.5 MoonLite Focuser
Orion ShortTube 130mm f/5 Reflector
Stellarvue SV102BV f/8.7 LOMO Doublet APO
Stellarvue SV90T f/7 Fluorite
Synta ShortTube 80
Stellarvue SV70ED
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drshr
professor emeritus
Reged: 06/09/08
Posts: 675
Loc: Darwin, Australia
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I think you will find that the 120ED is better at just about everything, esp if your mirror coating is a little past its best.
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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.
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meteorite
Vendor (meteorites)
Reged: 01/28/06
Posts: 268
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Thanks for the comments.
David, the 6 inch Reflector is on a plain vanilla dob mount.
-Walt
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RAKing
Carpal Tunnel
Reged: 12/28/07
Posts: 2092
Loc: West of the D.C. Nebula
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Your 6 inch Newt is a very nice instrument, but with the typical 20 - 22 percent CO it won't have any better contrast than a 120mm refractor anyway. So why not go for the better optics and totally clear aperture. I have a Newt, but it collects dust in the closet. I hate to fiddle with collimation and like the views better through the refractor.
You will need a mount to go along with your new tool - and it could be anything from a simple alt-az push along (like your Dob) to a GEM w/Goto.
The 120mm refractor is a very nice size - small enough and light enough to be Grab and Go for many, yet big enough to pull in a nice array of objects.
My .02,
Ron
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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.
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Lane
Carpal Tunnel
Reged: 11/19/07
Posts: 1515
Loc: Frisco, Texas
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Most people seem to feel that a refractor has about a 1.5" advantage over a dob. So a 4.7" refractor should be a little better than the 6" dob.
However you do lose resolution because that is based on the width of the main objective. So the dob will still split doubles better and show more stars in the core of a globular. Although they might be prettier in the refractor.
You lose a lot of light gathering ability because that depends on surface area and the dob has 62% more surface than that refractor. And whether the dob has an old mediocre mirror or a great mirror has very little to do with that value. So you will be able to see very faint things with the dob that will not be visible with the refractor.
Contrast is where the refractor excels, the central obstruction even a small one does reduce contrast. And contrast means you see the faint details better. So the bands on Jupiter will be sharper and contain more detail in the refractor and you will be more likely to see details in a faint galaxy as well.
So overall you will probably like a 4.7" refractor better than a 6" dob or a 6" sct.
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Mounts: CGEM, ORION SIRIUS, AT Voyager/motorized
SCTs: C6, C8, C9.25, C11,
Refractors: TV Pronto, Orion ED80
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4947
Loc: MA
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Ask this question in the reflector forum to get a "fair and balanced" perspective.
A 6" f/8 with a ~20% CO (1.2") can be an outstanding planetary scope. IMO, the 120ED, though a great scope (I have an EON120), would not be any better, assuming your 6" is decent one. There are pros and cons of size, weight, collimating, equilibration, viewing position etc., but at the eyepiece, you'd be hard pressed to see any difference and could just as well find the 6" Newt to be slightly superior. The place where refractors really shine is in lower power wide FOVs.
If you want an excellent refractor, by all means get the 120ED. It's an outstanding scope and value. Just realize the views won't be substantially different from what you're getting with your Newt.
Noted astrophotographer Damian Peach's website has an excellent page that illustrates, through simulations, the relative effects of varying aperture, % obstruction, optical quality etc.. It's quite illuminating.
Edited by Luigi (11/01/09 10:32 AM)
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Ennis
sage
Reged: 09/11/06
Posts: 328
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I recently purchased a Sky-Watcher Pro 120ED, and, contrary to the Sky-Watcher website, the telescope does not come with a right-angle, correct-image (RACI) finder (apparently, it originally did come with such a finder). Nor does it come with two long eye relief eyepieces. The telescope does come with a very nice "regular" finder and two average Chinese eyepieces, however, and a decent 2" diagonal. Sky-Watcher really needs to update its website. Having said all that, I still love my 120ED and recommend it. I actually prefer its mechanics over the EON 120.
Ennis
P.S. If you do get a Sky-Watcher Pro 120ED, I recommend that you also get a Scope Stuff 2" compression-ring visual back. It's a very nice upgrade to the 120ED and fits perfectly.
Edited by Ennis (11/01/09 10:14 AM)
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cuzimthedad
Just Be Cuz
Reged: 04/09/06
Posts: 3725
Loc: Sonoma, Northern California
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Based upon what you have stated about your observing habits and likes, I would say you are probably making the right choice. With that said, I am finding the better I get at collimating my dob, the more apoish views of stars I am seeing and I can't see much of a difference between it and my TV102 on them. However, I love all three of my scopes and have no bias for any of them. They all serve a purpose so I feel I can say, unbiased mind you  , that you should go for the 120ED and enjoy what it shows you.
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Dan
20" f/5 Obsession
Antares 1529
TV102
Various Naglers, Ethos, UO Orthos and TV Plossls
The Off Fisher Lane Irregulars
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 4076
Loc: S. Philadelphia, PA
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I use my 120ED more than my 12" dob for viewing the planets and the moon at high mags because of its tracking, rapid cool down time, lack of set-up and unbeatable contrast. It's a great scope! - j
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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.
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mathteacher
Carpal Tunnel
Reged: 05/13/07
Posts: 2060
Loc: SF Bay Area
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The 6 f/8 reflector is a venerable design. I think a good 120ED will be a keeper for life.
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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
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moonnerd
member
Reged: 12/18/08
Posts: 25
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Quote:
Noted astrophotographer Damian Peach's website has an excellent page that illustrates, through simulations, the relative effects of varying aperture, % obstruction, optical quality etc.. It's quite illuminating.
I don't want to hijack this thread, but this seems like a good place to talk about the wonderful link Luigi pointed us to. Are the conclusions on Damien's page basically what you find in real life?
If so, from comparing the photos in Damien's conclusion, it seems that the key hurdles to overcome are having optics at 1/4 wave or better, and an obstruction at 35% or less. After that, the main issue is aperture, assuming you'e comparing two equally good samples. Is that a fair interpretation?
Thanks,
rob
In that case, Wal (original poster) might be better off keeping his reflector unless it is too difficult to set up
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wfj
sage
Reged: 01/10/08
Posts: 260
Loc: California, Santa Cruz County
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Boils down to the scope that's used most.
For a while I'd use my refractors - long and short - the most. Then my cats - SCT's and MCT's. Then my newts - big, small, and long/short. I even set up pairs of them and did comparatives.
It all boiled down to "lazy" or "industrious" observation. If I was being lazy, the refractors got used more. If industrious, a larger newt got used the most.
On my logged observations, the vast (5x) majority were with a 10" newt - if I was being lazy with a refractor, I didn't log them, nor did I see anything new (other than comets). For a while I used my refractors for doubles exclusively, but when I got obsessive with finding/eliminating optical flaws in my newts (and lowering the CO to well under 20%) I no longer saw the point after A|B tests. Ditched all my long refractors. Kept one long newt - a 6" f/8.3.
I typically use short refractors for widest field views of subtle objects in dark sky, where contrast really matters - nothing beats them for this. In a pinch it's quite good past 400x with little CA. Shoot doubles with my newts, and have no complaints with the long newt - its a fantastically versatile scope which can be used on just about anything.
But when I need to check out an object being talked about, I pick the 10" newt for no muss no fuss show me the damn thing - it stands out so I find it quick in a 2 dg FOV. Keep it in a Rubbermaid storage container outside with a large desiccant = always cold and setup/teardown in two minutes.
Which is why the number of log entries are so, so high. Even when I'm resistant to doing so.
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Fomalhaut
sage
Reged: 08/16/08
Posts: 244
Loc: Switzerland
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Even if you'd compare to a 4-inch Apo:
Though a 6-inch Newtonian with minimized obstruction indeed CAN slightly (!) outperform a 4-inch-Apo on planets, the sum of the 4-inch-Apo's overall attributes excels the ones of the 6-inch-Newtonian:
Lesser susceptibility to decollimation, tube seeing/ground seeing, stray light (=> faint low contrast objects); more useful FOV, better in photographical applications...
Even more so is this the case if you compare the 6-inch-Newtonian to a 120mm-ED (which, by the way, can not be called a true Apo if it's not a triplet, but nevertheless - if it is a decent one - will certainly not be second to any 6-inch-Newtonian, neither on Jupiter's surface nor on any other target...).
I personally would not hesitate to choose, say a Tak TSA-120 (ED-triplet) over any 6-inch Newtonian in the world!
Chris
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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 (11/02/09 12:35 PM)
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roadi
professor emeritus
Reged: 08/18/07
Posts: 531
Loc: Denmark
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Quote:
Ask this question in the reflector forum to get a "fair and balanced" perspective.
A 6" f/8 with a ~20% CO (1.2") can be an outstanding planetary scope. IMO, the 120ED, though a great scope (I have an EON120), would not be any better, assuming your 6" is decent one.
I fully agree..
I once had an excellent 6" f8 planetary Newton, made by a company on the demand of a planetary scope. It had a 1" secondary, thin spider vanes (0.3mm) and a 200mm diam tube made of some synthetic materiel.. the optics was simply excellent but I didn't ask that time wich brand the mirrors were.. He was a meade dealer though!
It easily beated my 4" f15 Jaeger achromat on all objects especially Jupiter both resolution and contrast, and the 4" jaeger was/is no slough either just about equal an excellent 4" Apo on planetary observation.
I'm pretty sure that a well made 6" f8 planetary Newton (Right tube and about 16% CO) with excellent mirrors will be right up to any 120mm Apo, be it a triplet or doublet of any brand. Probably slight better!
I think it will boil down to wether one likes the design/look.. Newton vs Refractor design but in optical performance in the field the well made 6" f8 reflector won't take a second place to any 4-5 Apo but pretty sure the opposide way around.
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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..
Edited by roadi (11/02/09 06:38 AM)
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wfj
sage
Reged: 01/10/08
Posts: 260
Loc: California, Santa Cruz County
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Quote:
I personally would not hesitate to choose, say a Tak TSA-120 (ED-triplet) over any 6-inch Newtonian in the world!
Chris
Once I would have agreed with you Chris - I have looked through that Tak too. No longer. Do anything with high regard for quality and you get similar results. Even APO's have limits one is wise to respect.
My point is in regards to quality always trumping in minimalistic optics.
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Fomalhaut
sage
Reged: 08/16/08
Posts: 244
Loc: Switzerland
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Quote:
Quote:
I personally would not hesitate to choose, say a Tak TSA-120 (ED-triplet) over any 6-inch Newtonian in the world!
Chris
Once I would have agreed with you Chris - I have looked through that Tak, too...
=> 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
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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 (11/02/09 03:10 PM)
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2704
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I personally don't think you will see much difference on the planets or moon assuming that the optics of your reflector are decent.
The additional 1.25" of aperture of the reflector is going to negate almost all of the contrast loss imposed by the secondary and spider, and the extra brightness in the 6" is enough to notice at the eyepeice on deep sky and on planets.
If your ultimate interest is in planetary observing, I would recommend that you go to a bigger, higher quality reflector like an 8" f/6. Put it on a tracking platform if you need tracking and you can still come out cheaper than a 120ED scope on a decent mount.
Small refractors make WONDERFUL planetary scopes when compared to small reflectors, but it is hard to beat good quality aperture, and it is VERY hard to be LOTS of aperture. Anyone that has ever seen Jupiter in an 8" Portaball or 7" Starmaster will tell you that there aren't to many refractors made that can provide BETTER views.
A 120mm ED scope may not actually provide ANY IMPROVEMENT in planetery performance over your current scope unless your current scope has poor optics. If it is a Vixen or similar quality reflector, don't look for any "OMG LOOK WHAT I HAVE BEEN MISSING!" moments, because there won't be any. If the quality is not very good, then a 120mm ED scope may offer a SMALL amount of improvement.
I have owned a variety of small refractors up to 6", and a good 8" f/6 reflector with high quality optics and 20% secondary would make a better planetary scope than any of them (perhaps includeing the Astro-Physics 6" I own).'
Go bigger if planetary is your passion. Get a high quality 8" f/6 and learn to be patient at the eyepieces, and you will see more than any 5" APO made today.
I like the 5" refractor range of telescopes because of their flexibility, but I do 100% of my planetary viewing with large reflectors (A CAT at that!). I don't even bother aiming my 4" refractor at the planets anymore because they just don't really provide much in the way of serious planetary observing detail and a 5" is not much better. Even a 6" refractor is only ok for planets.
Good luck. Enjoy your 120ED if you get it. They are nice all around telescopes.
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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.
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AlienRatDog
Pooh-Bah
Reged: 07/15/05
Posts: 1094
Loc: Ann Arbor
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How do you think a C9.25 would do against a 127mm APO??
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Abe -- the poor PhD student
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12" LX200GPS-SMT w/UHTC
Explore Scientific 127mm Triplet ED APO
Losmandy GM8 EQ mount
Nagler 31mm, 17mm, 13mm, 12mm, 9mm, 2.5x Powermate
12X50 Binoculars
Understanding wife
One beautiful daughter, Emma-Rose (born 7-29-2009)
Twin boys (cats), half Persian/half Alley Cat but all Vermin!
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starrancher
professor emeritus
Reged: 06/09/09
Posts: 620
Loc: Northern Arizona
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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 .
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LXD75 AR5
LXD75 SN8
Series 4000 Plossls
Misc. other stuff
Fort Rock , Az .
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wfj
sage
Reged: 01/10/08
Posts: 260
Loc: California, Santa Cruz County
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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?
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Jared
Carpal Tunnel
Reged: 10/11/05
Posts: 2540
Loc: Piedmont, California, U.S.
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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.
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- 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
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RAKing
Carpal Tunnel
Reged: 12/28/07
Posts: 2092
Loc: West of the D.C. Nebula
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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
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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.
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2704
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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.
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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.
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stevew
Pooh-Bah
Reged: 03/03/06
Posts: 1148
Loc: Vancouver
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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?
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TV Genesis SDF
Meade 127ED
Antares 152
Celestron C5
Celestron C8
Celestron C11
Coulter Odyssey 8
16 Dobsonian
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roadi
professor emeritus
Reged: 08/18/07
Posts: 531
Loc: Denmark
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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?
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Regards Rodi
60mm Polarex, Sky90, µ210, SKW150 Binoscope
Vixen GpDx, Astro5, LX200
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Couple of diagonals..
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Fomalhaut
sage
Reged: 08/16/08
Posts: 244
Loc: Switzerland
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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)
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Patrick
Postmaster
Reged: 05/16/03
Posts: 7811
Loc: Franklin, Ohio
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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
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10" f/6 Truss Tube Newtonian
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AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
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Patricko
Carpal Tunnel
Reged: 01/30/07
Posts: 1534
Loc: SE New Mexico USA
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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. 
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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
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PJ Anway
Pooh-Bah
Reged: 06/04/03
Posts: 1142
Loc: Michigan's U.P.
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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? 
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PJ
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Wilsonman
Pooh-Bah
Reged: 01/30/07
Posts: 1088
Loc: S.E. PA
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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.
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mathteacher
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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.
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Regards, Mr. Wang . . . . . . . My gallery . . . . . . . I'm a refractor guy!
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Patrick
Postmaster
Reged: 05/16/03
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Loc: Franklin, Ohio
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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
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10" f/6 Truss Tube Newtonian
Celestron C6S-GT SCT
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
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Patrick
Postmaster
Reged: 05/16/03
Posts: 7811
Loc: Franklin, Ohio
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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
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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
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Vixen GP2 Photo Guider Mount
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drshr
professor emeritus
Reged: 06/09/08
Posts: 675
Loc: Darwin, Australia
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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.
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Doc
14" F5 DOB.
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Fomalhaut
sage
Reged: 08/16/08
Posts: 244
Loc: Switzerland
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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...
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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)
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 4076
Loc: S. Philadelphia, PA
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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
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Gord
professor emeritus
Reged: 01/06/04
Posts: 694
Loc: Toronto, ON, Canada
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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
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* Celestron C10/Normand Fullum primary
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roadi
professor emeritus
Reged: 08/18/07
Posts: 531
Loc: Denmark
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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?
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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..
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2704
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My experience is similar. Very small refractors may not need cooling, but at around 5" and larger, they do need to cool.
And you can stick a boundry layer fan on a Newt and start using it almost immeditaly (if the fan is well balanced or well vibration mounted).
I personallly would not recommend a 5" or 6" APO as a planetary scope to someone that wanted to do reallly serious planetary observing. They just aren't big enough. I HAVE a big refractor and a bigger reflector (OMG, a CAT!) and there is little to compare. In every area of performance, in dozens of side by side comparisons, the big reflector always showed more detail if I was patient (which you HAVE to be to do serous planetary observing, unless you live on the top of Mt Everest).
A high quality 8" f/6 would be a far better choice if planets were the primary target, and a 10" f/6 would be even better, though this starts to get hard to utilize.
I agree that the bias towards refractors on this forum in this case could be damaging. For planetary observing, the big f/6 and slower Newtonian reflector remains the instrument to beat. Dismiss all of the nonsense on seeing and cooling. Patiance and aperture make for the best planetary viewing. Paying more for a small refractor that can never show you MORE detail and more often than not will show LESS detail is a questionable investment to me if your passion is planetary observing.
If the OP just wants to change to a refractor and his current scope has good optics (as he implies), I think he will be moving sideways. But if he just WANTS a refractor, then hey, Ca CHING and it is done!
Me? I have never had the pleasure of looking though a refractor that could beat a good 10" f/6 Newtonian on planets. I imagine that even an 8" APO would struggle to match it. I have looked though a couple of dedicated 10" f/6 Newts (optomized secondary, curved vane spider, fans, dedicated to planetary observation, so somewhat narrow field of illumiation compared to more common light bucket designs) and they have been STUNNING.
I looked though an older Portaball once and just about fell out of the chair! If people have never used a Newt with a premium mirror, they could be fooled into thinking their refractors are magical. The reality is that for the money you would spend on a 120mm ED refractor, you can buy an high qualty 8" Newt (or buy a cheap one and have the mirror refigured) and STILL have money for a set of top quality planetary eyepeices!
So, I too think that the OP should move to a bigger reflector than a smaller refractor. If he moves up at all from his current scope, it is likely to be a baby step.
Anyone that has never seen Jupiter or Mars in a high quality 10" Newt with fans is missing a specatacular sight.
Make - my - funk - the "P-funk" and make my planetary scope a BIG reflector. 
Make the OPs scope whatever he wants.. LOL.
Regards.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
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