Seeking advice for 8" visual OTA. GSO RC or SCT?

[zathras (Mark)]

Hi everyone,

I'm interested in only visual (for now) viewing to set up in the back yard. I want an easy and quick setup that can plonk onto a permanent mounting post. The actual mount I will decide later.
From what I have read and understand, seems an SCT is the overall winner for ease of use and applicability to visual Astro. Compactness, optical quality, collimation, aperture etc.
So the choices I see are;
GSO RC f/8 which is an amazing price
Celestron/Meade 8" (EdgeHD/ACF) type OTA

Now the SCT OTAs are not attractive for their price, especially here in OZ. (Yes, I would really prefer the "corrected" optics for SCT).
The RC seems too good to resist but I have read reviews on these GSOs that remark it is not suitable for visual work.
I don't really understand that since the SCTs are f/10 and the f/8 RC should be "better" for a wider field.
Why would the RCs not be a good comparison to the SCTs for visual work?
Any comments/advice please?

[RickS (Rick)]

Originally Posted by zathras

Why would the RCs not be a good comparison to the SCTs for visual work?
Any comments/advice please?

RCs generally have a much larger central obstruction than SCTs and hence provide lower contrast. Have a look at: http://legault.perso.sfr.fr/obstruction.html

Cheers,
Rick.

[allan gould]

For visual I would recommend an 8" Meade ACF scope - flat field and cheaper than the Celestron model. I would put it on an HEQ5 Pro mount and have a great portable set up.

[zathras (Mark)]

Originally Posted by RickS

RCs generally have a much larger central obstruction than SCTs and hence provide lower contrast. Have a look at: http://legault.perso.sfr.fr/obstruction.html

Cheers,
Rick.

Thanks for this very interesting link Rick.

[gregbradley]

RC design typically has a large secondary and thus not great for visual. Although those who actually own one could make a definite statement.

SCTs though are great for visual.

Greg.

[Satchmo]

I think typical 8" SCT's are about 38% obstruction at the secondary baffle ( for the F10 - the F8 may be larger). If you had to pick the one as the lesser of two evils it would be the SCT !

[zathras (Mark)]

Originally Posted by gregbradley

RC design typically has a large secondary and thus not great for visual. Although those who actually own one could make a definite statement.

SCTs though are great for visual.

Greg.

Greg the specs on the GSO RC are 47% by diameter!! That does put a crimp on the RC.
Now the Meade OTA Allan suggests is around $1600AUS, more than twice the RC.

[netwolf]

Mark, I would look at the used market for an SCT, some good deals to be had locally. Some very good deals to be had from US. Have a look at Astromart. The real headache is getting finding someone willing to ship it and 2 who is capable of packing it well for shipment. I had a C8 Fastar sent over and it arrived safe and sound.


Have you ruled out a 8" Newt or Dob? If only visual then this or a 10" are
good bang for buck.

BTW I did notice a LX90 8" EMC in the used section price is very good compared to the new ACF OTA cost. IMHO a very good scope, my greatest regret is i sold mine. By far the best grab and go I ever had.

Edit: I just noticed there is more than one LX90 on sale one is a bit newer UHTC model.

Regards
Fahim

[Terry B]

Another option is the vixen VC200L which is nice both visually and for imaging.
I have had one for many years and dont think I will ever sell it.

[MortonH]

Newtonians will generally have smaller secondaries (unless optimised for imaging) and therefore better contrast. I have a Skywatcher black diamond f/5 and it's pretty good. Same as this one currently for sale in the classifieds. Much cheaper than a SCT too!

http://www.iceinspace.com.au/forum/s...d.php?t=102784

[zathras (Mark)]

Originally Posted by netwolf

Mark, I would look at the used market for an SCT, some good deals to be had locally. Some very good deals to be had from US. Have a look at Astromart. The real headache is getting finding someone willing to ship it and 2 who is capable of packing it well for shipment. I had a C8 Fastar sent over and it arrived safe and sound.


Have you ruled out a 8" Newt or Dob? If only visual then this or a 10" are
good bang for buck.

BTW I did notice a LX90 8" EMC in the used section price is very good compared to the new ACF OTA cost. IMHO a very good scope, my greatest regret is i sold mine. By far the best grab and go I ever had.

Edit: I just noticed there is more than one LX90 on sale one is a bit newer UHTC model.

Regards
Fahim

Fahim,

I am worried about transport if I buy from the US. I saw a used Vixen VC200L recently on eBay from the UK but skipped it for this same reason. The prices are soo tempting though.
Thanks for the tips on the LX90, I'll have a look.

I own a 12" Newt but I'm sort of time-poor now and would just like to take out a smaller compact scope quick and easy. (I do have a slight concern I may be dissapointed a little going down in aperture.)
You know what? Now thinking it was a mistake to go too large?!
What's the old saying: Best scope is the one you use more often.


Thanks for your comments and advice.

[zathras (Mark)]

Originally Posted by MortonH

Newtonians will generally have smaller secondaries (unless optimised for imaging) and therefore better contrast. I have a Skywatcher black diamond f/5 and it's pretty good. Same as this one currently for sale in the classifieds. Much cheaper than a SCT too!

http://www.iceinspace.com.au/forum/s...d.php?t=102784

Yeah, that's a great price.
Prob should have got something like this in the first place.

[zathras (Mark)]

Originally Posted by Terry B

Another option is the vixen VC200L which is nice both visually and for imaging.
I have had one for many years and dont think I will ever sell it.

Terry,

Had a look at this model when I saw it on eBay. Looking specs http://www.chuckhawks.com/vixen_VC200L_telescope.htm , it has 40% secondary. Which is at least smaller than the GSO RC.
Now I regret not going for it.

[ausastronomer (John Bambury)]

Originally Posted by gregbradley

SCTs though are great for visual.

Greg.

Hi Greg,

I can't agree with this comment at all.

There are a whole lot of reasons why someone might choose a SCT as their scope of choice for visual astronomy, including convenience, lack of storage space, or dual purpose as an imaging platform.

The quality of the views isn't a reason anyone would choose a SCT, unless they don't know what they are looking at. Look at all the specialist visual lunar/planetary observers, look at all the specialist double star observers, look at all the specialist variable star observers, look at all the specialist deep sky observers, you will be lucky if you find any of them using a SCT for visual work.

The pure physics of the design precludes them from being the optical equal of a newtonian or a refractor.

1) Large Central Obstruction
2) Closed tube design with corrector plate hinders fast cooling
3) More air to glass surfaces introduces additional aberrations and light loss.
4) The optical quality of the scopes themselves in many cases is poor. Although there are a few good ones. I just haven't seen very many.

Mark,

If you don't plan on imaging in the foreseable future I would be giving serious consideration to downsizing your current 12" newtonian to a 10" and being done with it. Sell the 12" on IIS and buy a 10". There isn't a huge difference in the views, but there is an enormous difference in portabality, particularly if you went with a collapsible tube version. A 10" newtonian is going to be a better visual scope on just about every single target as compared to a SCT or RC.

If you do plan on imaging one of the Advanced Come Free scopes would be a good choice as an "allrounder".

Cheers,
John B

[swannies1983 (Dan)]

I have never owned a SCT but have a RC8. At this stage, I have purely used the RC8 for imaging. The only time I have "looked" through the scope is to find my DSO that I plan to image. Mind you, I have had a brief look at Jupiter and I wasn't impressed. Then again, the seeing may not have been great.

[Poita (Peter)]

Originally Posted by ausastronomer

Hi Greg,

I can't agree with this comment at all.

There are a whole lot of reasons why someone might choose a SCT as their scope of choice for visual astronomy, including convenience, lack of storage space, or dual purpose as an imaging platform.

The quality of the views isn't a reason anyone would choose a SCT, unless they don't know what they are looking at. Look at all the specialist visual lunar/planetary observers, look at all the specialist double star observers, look at all the specialist variable star observers, look at all the specialist deep sky observers, you will be lucky if you find any of them using a SCT for visual work.

The pure physics of the design precludes them from being the optical equal of a newtonian or a refractor.

1) Large Central Obstruction
2) Closed tube design with corrector plate hinders fast cooling
3) More air to glass surfaces introduces additional aberrations and light loss.
4) The optical quality of the scopes themselves in many cases is poor. Although there are a few good ones. I just haven't seen very many.

Mark,

If you don't plan on imaging in the foreseable future I would be giving serious consideration to downsizing your current 12" newtonian to a 10" and being done with it. Sell the 12" on IIS and buy a 10". There isn't a huge difference in the views, but there is an enormous difference in portabality, particularly if you went with a collapsible tube version. A 10" newtonian is going to be a better visual scope on just about every single target as compared to a SCT or RC.

If you do plan on imaging one of the Advanced Come Free scopes would be a good choice as an "allrounder".

Cheers,
John B

I keep seeing all these reasons why newts give better images than SCTs, but a lot of those disadvantages don't play out in actual use.
You do want to have cooling for the SCT, mine gets down to ambient in under 20 minutes with the fans.
The light-loss is a bit of a furfy, I challenge anyone to show any noticeable light-loss from a current model coated SCT vs a same diameter newtonian. Side by side I have never found anyone that can discern a feature in a similar diameter Newt that is not as clear in my SCT.
There are more than 'a few good ones' but like many dobs and SCTs a lot of people don't collimate theirs properly. This will make any scope appear to be a poor performer.

The optical quality in some dobs are poor, the optical quality in some SCTs are poor. Whichever scope you buy, get a star test done. The optics in my C9.25 HD test excellently and it is a joy to look through and to image with. I've owned a VC200L before, and they are also a good scope.
But if I ould only have one scope (which is what has happened now) I would go the SCT... and I did

Whatever you buy, make sure the optics are decent, and if they aren't, then take it back.

[Capricorn1(Tom)]

Concur with Peter's comments, I have a C14(farstar version) and a C8...the C8 is a fantastic visual plateform---nice and light(and yes I have refractors and a mak-newt to make a judgement). Also if you can afford a hyperstar for the C8 in the future---you can image a F2----google images on the internet and see for your self.

Cheers

[ausastronomer (John Bambury)]

Originally Posted by Capricorn1(Tom)

Concur with Peter's comments, the C8 is a fantastic visual plateform---nice and light(and yes I have refractors and a mak-newt to make a judgement).

Cheers

Hi Tom,

Am I correct in assuming that in addition to the C8 and the C14 you mentioned, you have an 8" refractor and an 8" Mak Newt which you are comparing against the C8?

Cheers,
John B

[Capricorn1(Tom)]

Good Day John

My comment was a generalization. I agreed with Peters comments....if I was to have one scope it would be a SCT. The other scopes I have are a 150 Mak-Newt, WO Megrez 88 and a WO Zenithstar 80.

Cheers

[ausastronomer (John Bambury)]

So Tom you really haven't actually compared you're 8" SCT against any other 8" telescopes of different optical design?

Cheers,
John B