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Is an SCT a good all-rounder for visual + imaging?

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#1 Jarrod

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Posted 13 February 2013 - 09:20 AM

Thinking of getting a Celestron C6 or C8 or ?? on their new VX mount. This will be my first "serious" scope and I want it to be something that:

a) Provides good visuals
b) Is reasonably good for imaging DSOs, the moon, and planets (priority in that order).
c) No more than $2k for scope + goto mount.

I considered a mounted newt, but realized that all the added weight would require a much sturdier and $$ mount, making the whole thing much less convenient to move and store than a SCT. Someday I may add a 10-12" dob as a dedicated visual scope. In the meantime I need an all-rounder.

What about the size? My concern is aperture vs. field of view. Obviously the bigger mirror can collect more light. But the C6 and C8 are both f/10 or f/6 with a reducer. How much does the difference in FOV at prime focus impact astrophotography? Can you put a widefield in and use the projection method with reasonable results on these scopes? Basically looking to understand what are the tradeoffs.

Sorry - I know these are very basic questions, but I'm trying to get up to speed so I can make an informed decision.

#2 Eddgie

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Posted 13 February 2013 - 10:34 AM

As you have already surmized, but scopes are natively f/10 without a reducer and f/6.3 with a reducer.

For extended targets, brightness has nothing to do with aperture. It is totally a function of focal ratio and focal ratio alone, and this is true for both visual and imageing use.

For imaging an extented target, if you use the same camera at the same exposure in both scopes at f/10, you get the exact same brightness in each image. Same at f/6.3. For a given expousre time, the image will be just as bright in each scope.


For visual observing of extended objects (nebula, galaxies, and planets), if you have two f/10 telescopes and you use the same eyepeice in each, you get the same brightness as well. So, brigthness for extended targets is simply a function of focal ratio.

In the case of the C6, for whatever reason that only Celetron knows, they used a very small baffle, so this means thatwhen imageing you will get about the same size true field from it as you will get form a C8 before vignetting starts.

So, the C6 will give just as bright an image, but at a smaller image scale. No wider field though because of the vignetting imposed by the small primary baffle.

For visual use, you get more contrast and more angular resolving power, and better limiting magnitude (fainter stars visible in Globulars).

The C6 will on the other hand be lighter and easier to use for long exposures becasue it will make less demand on the mount.

My own recommendation would be for the C8 because in most things to do with telescope performance when used visually, a bigger aperture is generally a better aperture.

The C8 can give a field that is almost as wide and much better illuminated than a C6 when used visually. The C6 gains a lot of focal lenght when used with 2" diagonals, and will loose a lot of illumination at the edge of the field when used this way. The C8 can be used with eyepeices like a 35mm Panoptic and remain very well illuminated at the edge of the field makeing it (to me) a better wide field telescope.

And for planets and deep sky observing, the extra aperture allows for higher magnifications at the same brightness, which helps greatly in observing.

But a C8 weighs more, and there will be many people that say that the scope you use the most is the best scope (I personlly think bigger is just about always better, but that is me).

So, for exposure times, both will give about the same brightness and about the same well illuminated true field size, but the C8 will give a bigger image scale.

For visual, the C8 has the advantage of better resolving power, better contrast transfer, and a field that is more fully illuminated when using very low power wide field eyepeices. It will be better for just about all observing.

But it weighs more.

In my opinion, everyone should have a C8. The penalty in size and weight over a C6 is simply to small to me to be meaningful, though it is a factor when it comes to mount capacity for imageing.

People will think I am bashing the C6 though. I am not. For people with bigger scopes, the C6 can make a fine smaller scope.

But if I could only have one scope (and I do have a C5, a C8, a 6" APO, and a C14), it would be the C8..

LOL. Only kidding.. Dude.. It would be the C14. :roflmao: By my C8 would be my second choice.

But seriously, if you can only have one or the other, my own suggestion for all of the requirments you have put forward would be a C8. It will be better at imageing and at visual use for the requirements you specified.

Again, I am not C6 bashing, but the C8 does everything as well or better than the C6 in a package that is only a bit bigger and a bit heavier. The C6 might make a great second scope, but for a primary scope, the C8 to me is about 72% better.

#3 RichD

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Posted 13 February 2013 - 10:50 AM

Yes.

#4 REC

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Posted 13 February 2013 - 10:57 AM

An 8" SCT is a great all around scope. Get yourself 3-4 EP's and a 2" dielectric diagonal, a dew shield, a chair and you good to go! Fork mount is ok for viewing a short exposures and easy to point and use. GEM is bigger, but better for AP.

Have fun and welcome to CN:)

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#5 Julio

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Posted 13 February 2013 - 11:14 AM

C8..trust me, thay are fantastic if you get a good one. Celestron's quality control has improved quite a bit.

#6 t.r.

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Posted 13 February 2013 - 01:33 PM

There is good reason that the 8" SCT has garnered the reputation it has...BEST ALL AROUND, JACK OF ALL TRADES, BANG FOR THE BUCK! As an only scope...in a heart beat! ;)

#7 Crow Haven

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Posted 13 February 2013 - 02:35 PM

+1 :grin:
I've enjoyed both a C-5 and C-8 since the 1980's. So much so, in fact, that I recently ordered a new C-8 SE XLT orange OTA (should have it by the 19th) to replace my old C-8 that was bare-bones with only the "special coatings". I already have a f/6.3 reducer/corrector, and a 35mm Panoptic for wider fov use when needed. The C-8 is my ultra-portable med-large scope vs my 10" dob, which although is portable is certainly a bit less so. :lol:
---Maya

#8 WarmWeatherGuy

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Posted 13 February 2013 - 04:20 PM

You should watch this video about how important it is to determine your field of view before you buy your telescope and camera.

#9 jgraham

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Posted 13 February 2013 - 06:17 PM

I consider my 8" SCT to be the most versatile visual/imaging scope that I own.

#10 GeneT

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Posted 13 February 2013 - 06:33 PM

There is good reason that the 8" SCT has garnered the reputation it has...BEST ALL AROUND, JACK OF ALL TRADES, BANG FOR THE BUCK! As an only scope...in a heart beat! ;)


:grin: agree :grin:

#11 Jarrod

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Posted 14 February 2013 - 12:22 AM

Thanks for the feedback, especially Eddgie for taking the time to explain the differences between the C6 and C8 in such detail.

The C8 seems like a winner, until I go read the answers to basically the same question asked in the imaging forum. Apparently imaging is not possible unless you have a refractor :grin:

Jokes aside, it seems there is no easy answer.

#12 tim53

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Posted 14 February 2013 - 01:13 AM

I prefer newts and real cassegrains, but an 8" SCT is hard to beat for an all-rounder, as others have said.

-Tim.

#13 kansas skies

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Posted 14 February 2013 - 08:10 AM

A 6" SCT and an 8" SCT will take about the same amount of time to reach thermal equilibrium, so that shouldn't be much of an issue in making a decision. The 8" will take up more space and be somewhat heavier, making it a little less portable. Only you can decide if that's an issue. As already stated, given the same eyepiece, the 6" will offer a smaller image within a wider field of view at the same level of brightness. By selecting different eyepieces of appropriate focal lengths, it's possible to achieve the same field of view in both, in which case the 8" will present a brighter image. In addition, the 8" offers better resolution and will show fainter stars. That being said, either should work well for visual use and for photography. The mount required for the imaging might then be more of a factor.

Bill

#14 Illinois

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Posted 14 February 2013 - 08:32 AM

forget 6 inch! Use 8 inch for lifetime! If you have 6 inch then you will think about that should get 8 inch!

#15 Jarrod

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Posted 14 February 2013 - 09:43 AM

In addition, the 8" offers better resolution and will show fainter stars. That being said, either should work well for visual use and for photography. The mount required for the imaging might then be more of a factor.


Can we talk about that for a minute? I'm pretty set on getting the new Celestron Advance VX mount. Really can't see spending much more than that on a mount to start with, until/unless I'm *certain* that astrophotography is something I'm going to pursue longer-term.

So, I'm thinking really hard about the C8/VX package for around $1600.

#16 drbyyz

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Posted 14 February 2013 - 11:08 AM

I would push you towards the 8" as well. It is a very noticeable improvement over a 6" and most people have no issue with handling it...they aren't huge.

#17 bilgebay

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Posted 14 February 2013 - 11:29 AM

Just go the extra mile and buy the Edge 8". You will not regret it.

#18 Escher

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Posted 14 February 2013 - 11:32 AM

Just go the extra mile and buy the Edge 8". You will not regret it.


Yes!!

Get the 8" Edge and a CG5-ASGT and done... Its enough to get you going and you can do *some* AP with it... you will be able to resell the mount and upgrade to a heavier mount down the road.

#19 Jarrod

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Posted 14 February 2013 - 01:58 PM

So you are saying this one (I'd get it with the new AVX mount) is well worth the extra $400? What is this "Fastar" thing? f/2.8??!!

Do these things ever go on sale? $2k is at the upper limit of my budget and I'd need to still get some AP accessories (reducer, t-ring, filters, etc, etc.).

#20 Ed Wiley

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Posted 14 February 2013 - 03:53 PM

I vote for an Edge. Mine is on a Losmandy G-11--excellent mount. I have not experience with Vixen mounts but if you are contemplating astrophotography I would recommend doing some research as the mount is perhaps the most important component of any astrophoto system. This is not so important with solar system objects and webcams, but it is critical for DSOs. The usual formula is to keep the OTA+accessories about 1/2 the stated capacity of the mount. Many units are sold "undermounted" to the frustration of the budding astrophotographer. Investigate carefully.

Ed

#21 ahlberto

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Posted 14 February 2013 - 04:05 PM

Get a C8 Edge and a heq5 /cg5 mount,-a great combo for visual and for astropics. :smirk:

#22 northernontario

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Posted 14 February 2013 - 08:58 PM

I don't image, but if I did I would use a GEM.

I do observe however. And I do lots of it.

I have three scopes, one of each. I like them all, but...(I hope the other scopes aren't listening....I really love my SCT, as a matter of fact, my best planetary observations have been with the SCT. Mars, Saturn, Uranus, Venus and yes, even Pluto)

Most Messier Galaxies are eye candy in an 8 inch SCT.

I am very pleased with my Meade LX 200 Classic. It has been an amazing work horse over the years, and the optics are incredibly sharp. No regrets here.

jake

#23 cavefrog

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Posted 15 February 2013 - 12:00 AM

a Fastar is an optical unit that replaces the secondary mirror in the OTA. a camera then mounts on the fastar, eliminating the rest of the focal length. With the elimination of the rest of the focal length, it now becomes a very fast OTA that will make images in a very short amount of exposure time. your OTA has to be Fastar compatable, meaning it already has a removable secondary and ready to accept the Fastar. otherwise one has to get a converter kit to make it so.

hope this helps.

Theo

#24 mmalik

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Posted 15 February 2013 - 12:37 AM

Apparently imaging is not possible unless you have a refractor :grin:

Jokes aside, it seems there is no easy answer.


Not an easy answer. SCTs are primarily a visual platform; can they be used for imaging, sure, but they come second to refractors in that regard. Determine your ‘primary’ goal, then pick either SCT or refactor based on that.

In case imaging is your primary goal, then what comes before the scope is the mount. VX seems like a weaker contender for astrophotography. Thx

#25 Gary Z

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Posted 15 February 2013 - 01:16 AM

Personally, I have an 8SE with a GPS mount. Love the scope. While I am quite jazzed with the new VX mount, consider that the C8 OTA, according to manual weighs in at 24 lbs. The max payload for the VX mount is 30 lbs. Since I do not have an equatorial mount, I leave the following question/concern in far more experienced hands....Is the VX mount a reliable mount for an 8" OTA?






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