New GSO Classical Cassegrains

[Doc]

12 minutes ago, iPeace said:

I keep looking at these; very much inclined to try one for visual.

I do too, the price is good as well.

[AstroFin]

The 6 inch model seems to be available in Europe now. The price is €399 at Astroshop, sounds like a superb deal to me! ?

https://www.astroshop.eu/telescopes/ts-optics-cassegrain-telescope-c-154-1848-ota/p,60781

[Bob Curtiss]

I have owned numerous SCTs, Newts, MAKS and Refractors of both varying size and focal lengths over the past 50 years. I purchased two GSO f:12 classic cassegrains, the 6" a year ago and an 8" very recently but long enough to draw some conclusions. The f:12 is free of coma and that is to the edges of an UWA 20mm Meade series 5000. Both scopes are 100% achromatic, they feature quartz mirrors with 96% reflectivity. This is just about equal to a 7" and a 9" in either configuration given the difference between standard reflectivity found in many scopes. There is no corrective lens, the tubes are fully baffled and while the secondary is present as are the spiders, the contrast is excellent with a velvety black background against fully corrected objects. I have heard the 14mm Meade UWA compromised in another forum but those who use it don't know how fine an eyepiece it truly is. Again, edge to edge sharpness with a huge field of view. The same holds true of the 8.8mm and 5.5mm. These are bargain basement eyepieces compared to TV and some others and yet the panorama and field flatness is negligible for the price. Collimation is critical in the classic cassegrains. Yet, if you find collimation of the secondary an issue, you will likely find the same with a reflector or SCT. I purchased Bob's Knobs for these fine scopes and precise collimation can be had with a collimation eyepiece and results in images that are incredibly sharp. I am confident that magnification on transparent skies at a decent altitude above the horizon will allow me to push these to 60x - 80x/inch on close doubles or planets with no more degradation than you'd get at the suggested 50x max. They are compact, lightweight for size and best of all, feature three large setback rings of 2" and to of 1" to be used alone or stacked or removed completely. I find the 2" incredibly well made. Taiwan GSOs are light years ahead of Synta/Chinese optics and the rings will allow the use of cameras, autoguiders and on the 8" it features a top Vixen rail for accessories. I paid tax free, $499 US with free shipping for the 6" and $899 US for the 8" from Agena Optical. They have a master optician check each and every GSO (only) scope they sell out for optical perfection, cosmetics and more. Also featured is a dual speed 10:1 Crayford focuser on the back of the OTA. They are about as good as you can get and a lot more for the money compared to what is on the market. No mirror flop because they are not a part of the focusing....GREAT TELESCOPES! I would know and if you want to compare field flatness, light gathering power and all of the things that a similar priced MAK or SCT can't beat...try a GSO classic cassegrain....you won't be displeased. In fact you'll wonder why you bought either the MAK or the SCT instead.....Oh, standard features also include  a full length Vixen dovetail on the 6" and a Losmandy D plate 20" long on the 8". If you have a Celestron mount that doesn't accept the wider Losamady, two adapters are available that allow the 8" to fit a Vixen dovetail. I used one from Orion that needed shimming to fit, a simple and easy way to go for about $5 in parts. 5 STAR RATING ON GSO and I own another GSO f:5 newt that performs marvelously with flat fields with the 82 degree UWA's and using an inexpensive GSO coma reducer. Enhanced mirrors in that scope as well! 

[Alan White]

On 15/09/2018 at 10:38, iPeace said:

I keep looking at these; very much inclined to try one for visual.

So do I, we are too alike Mike!

It does sound an interesting telescope, very compact as well.
Good job I am trying hard to save my pennies for a new mount, otherwise my wallet would have flexed.

[Alan White]

1 hour ago, Bob Curtiss said:

I have owned numerous SCTs, Newts, MAKS and Refractors of both varying size and focal lengths over the past 50 years. I purchased two GSO f:12 classic cassegrains, the 6" a year ago and an 8" very recently but long enough to draw some conclusions. The f:12 is free of coma and that is to the edges of an UWA 20mm Meade series 5000. Both scopes are 100% achromatic, they feature quartz mirrors with 96% reflectivity. This is just about equal to a 7" and a 9" in either configuration given the difference between standard reflectivity found in many scopes. There is no corrective lens, the tubes are fully baffled and while the secondary is present as are the spiders, the contrast is excellent with a velvety black background against fully corrected objects. I have heard the 14mm Meade UWA compromised in another forum but those who use it don't know how fine an eyepiece it truly is. Again, edge to edge sharpness with a huge field of view. The same holds true of the 8.8mm and 5.5mm. These are bargain basement eyepieces compared to TV and some others and yet the panorama and field flatness is negligible for the price. Collimation is critical in the classic cassegrains. Yet, if you find collimation of the secondary an issue, you will likely find the same with a reflector or SCT. I purchased Bob's Knobs for these fine scopes and precise collimation can be had with a collimation eyepiece and results in images that are incredibly sharp. I am confident that magnification on transparent skies at a decent altitude above the horizon will allow me to push these to 60x - 80x/inch on close doubles or planets with no more degradation than you'd get at the suggested 50x max. They are compact, lightweight for size and best of all, feature three large setback rings of 2" and to of 1" to be used alone or stacked or removed completely. I find the 2" incredibly well made. Taiwan GSOs are light years ahead of Synta/Chinese optics and the rings will allow the use of cameras, autoguiders and on the 8" it features a top Vixen rail for accessories. I paid tax free, $499 US with free shipping for the 6" and $899 US for the 8" from Agena Optical. They have a master optician check each and every GSO (only) scope they sell out for optical perfection, cosmetics and more. Also featured is a dual speed 10:1 Crayford focuser on the back of the OTA. They are about as good as you can get and a lot more for the money compared to what is on the market. No mirror flop because they are not a part of the focusing....GREAT TELESCOPES! I would know and if you want to compare field flatness, light gathering power and all of the things that a similar priced MAK or SCT can't beat...try a GSO classic cassegrain....you won't be displeased. In fact you'll wonder why you bought either the MAK or the SCT instead.....Oh, standard features also include  a full length Vixen dovetail on the 6" and a Losmandy D plate 20" long on the 8". If you have a Celestron mount that doesn't accept the wider Losamady, two adapters are available that allow the 8" to fit a Vixen dovetail. I used one from Orion that needed shimming to fit, a simple and easy way to go for about $5 in parts. 5 STAR RATING ON GSO and I own another GSO f:5 newt that performs marvelously with flat fields with the 82 degree UWA's and using an inexpensive GSO coma reducer. Enhanced mirrors in that scope as well! 

Bob, interesting feedback, thank you.

Have you replaced Celestron or Meade SCT's with these?

 

[johninderby]

I have the TS Optics 8” version and have been very impressed with it. A big srep up in performance compared to my old Skymax180..A great advantage over a mak or SCT is the lack of dew problems and faster cooldown.

 

Edited November 25, 2019 by johninderby

[John]

A further review of one of these interesting scopes has appeared recently on another forum:

https://www.cloudynights.com/topic/686955-gso-8-inch-true-cassegrain/

The most interesting comments in that review for me, relate to the effective aperture of the instrument. Are there variations in spec for these scopes ?

 

[johninderby]

I think you’ve run into the typical CN “experts” who have never actually seen one and don’t know what they are talking about. The ones that have actually used one seem very positive.

While they use the same tube as the RC version inside they are a lot different with a much smaller obstruction and different mirrors. Think many are confusing the specs for the RC version with it’s big central obstruction and the CC. The early RC scopes had focuser problems but now sorted out.

You can buy a focuser tilt unit if you want but not needed for visual. The stock focuser is not bad at all but replaced mine with a Baader Steeltrack refractor focuser.. I have owned two C8s and they would be totaly outclassed on lunar / planetary compared to the classical cassegrain. which has better contrast and will take a lot higher magnification. The C8 has advantages for DS0’s when used with a focal reducer though.

One of the best features of the CC though is it’s not affected by dew unlike of course SCTs or Maks.and the shorter cool down time.   🙂

This is one of my all time favourite scopes. Impresses me every time out and such a pleasure to use. 👍🏻👍🏻👍🏻

Edited January 2, 2020 by johninderby

[Chris]

On 07/07/2018 at 12:44, Davey-T said:

Only 33% central obstruction 

Dave

38% for the 6", pretty much the same as a 6" SCT. Could be a cheaper option than a SCT without the dew issues, but I'm sceptical for some reason.

[johninderby]

I’ve not seen much on the 6” version but it is a lot cheaper than the 8” so is it as good? Having had the 8” SCT as well as the CC for me it’s a no contest for lunar / planeary observing. However that is the thing to keep in mind. It is a specualist lunar / plantary scope. 

[Chris]

34 minutes ago, johninderby said:

I’ve not seen much on the 6” version but it is a lot cheaper than the 8” so is it as good? Having had the 8” SCT as well as the CC for me it’s a no contest for lunar / planeary observing. However that is the thing to keep in mind. It is a specualist lunar / plantary scope. 

The 6" has 96% reflectivity on it's mirrors, whilst the 8" has 99%. Not sure why the difference? 

You're saying the CC is better for lunar? 

[vlaiv]

31 minutes ago, johninderby said:

I’ve not seen much on the 6” version but it is a lot cheaper than the 8” so is it as good? Having had the 8” SCT as well as the CC for me it’s a no contest for lunar / planeary observing. However that is the thing to keep in mind. It is a specualist lunar / plantary scope. 

Don't know, I would not label it as one trick pony. It scores rather high on my "quintessential do-it all beginner scope" list

You know, when people come and ask - is there a scope that can do it all - a bit of DSO observing, a bit of planetary observing, but I want also to be able to take pictures of those planets and the moon, and you know those nice looking colorful images of galaxies - want those as well. Btw, I live in center of major city and sky is really bright, but regardless I want to see it and don't mind using gadgets - EEVA. And yes, my budge is limited to ...

- it's relatively cheap (bested only by newtonian in 6" class and not by much - about 50% or so)

- It's compact and light(ish) - can be carried by EQ3 / EQ5 class mount (again reduces price of the mount to fit within budget constraints)

- it is 6" scope - meaning rather large aperture - good for dso and planets (light gathering, resolving power)

- it has about 40mm fully illuminated field - it can use 2" eyepieces with large field stop, although focal length is large it is not strictly narrow field scope.

It can almost frame M45 with GSO superview 38 mm EP

- again same illuminated field and slow F/ratio means that it will give enough FOV for imaging:

- for planets - it's obviously good for both imaging and observing

- with eyepiece projection, I think it is also good for EEVA (something that I'll test out with even slower F/13 scope, hopefully soon).

 

[johninderby]

They both have 96% reflectivity. There is a mistake on the TS website. 

The CC has better contrast and will take a lot more magification than either the SCT or MAK. My 8” CC gives better views than my 10” dob for lunar. Also the build quality is better than the SCT or MAK. Had someone take a look at the CC and he was impressed by the build quality and he owns a Tak Mewlon.

Yes it certainly can perforn on DSOs but it’s on lunar / plaetary where it is something special.

Edited January 3, 2020 by johninderby

[vlaiv]

2 minutes ago, johninderby said:

They both have 96% reflectivity. There is a mistake on the TS website. 

All of RC range is said to have 99% dielectric coatings on both primary and secondary, there is graph of reflectivity included as well on TS - which leads me to believe that is genuine claim.

These CC scopes share quite a bit with RC line - same/similar tube, same focuser, both have hyperbolic secondary, and prices are about the same (a bit larger for RC). It's not far fetched that mirrors have been coated to 99% with dielectric coatings as well.

[johninderby]

There was a discussion on CN on the subject of reflectivity and both GSO  and Orion  are claiming 96% so I’ve gone with the safe option of just claiming 96%.  Whichever is correct it is still a great performer.

Would like to see a proper review of the 6” to see how it compares to the 8”.

[johninderby]

Having another look at the manufactures specs for this scope they are claimng “better than 96%” reflectivity. 🤔

Not going to be too bothered by the precise figure though. It simply works brilliantly and wouldn’t hesitate recoomending this scope. I love it 👍🏻👍🏻👍🏻

Edited January 3, 2020 by johninderby

[Charles Kirk]

I wonder why they didn’t make an f/12 RC instead, which would be have a smaller central obstruction than the current f/8 models. I suspect that they wanted clearer product differentiation and saw a market for the classical Cassegrain design. No corrector plate to dew up saving the cost of a dew shield is certainly attractive.

[vlaiv]

2 minutes ago, Charles Kirk said:

I wonder why they didn’t make an f/12 RC instead, which would be have a smaller central obstruction than the current f/8 models. I suspect that they wanted clearer product differentiation and saw a market for the classical Cassegrain design. No corrector plate to dew up saving the cost of a dew shield is certainly attractive.

My guess is that they simply put existing products / manufacturing lines together to make new product and it worked well.

People expect "fast" systems for imaging, and their RC line due to large central obstruction is primarily considered imaging instrument - so they utilized F/8 design. My guess is that they have machine manufacturing of mirrors and that these machines can be set up for a certain "profile of the curve" - stronger curvature probably requires different tools or something like that. They have hyperbolic secondaries in RC line and they have parabolic primaries for their newtonian line. I just think they put two together to make new Cass line. Cost effective way to get new product out.

Designing new F/12 RC line would probably require change of tooling for machines as it would require slower curves on hyperbolic mirrors.

[johninderby]

Some interesting info on the CC vs RC.

http://www.dreamscopes.com/pages/projects-04/ccvrc-04.htm

[johninderby]

The GSO CC is actually a “fast” design. CCs were much more commonly f15 to f20 or slower.

[Live_Steam_Mad]

6 hours ago, johninderby said:

They both have 96% reflectivity. There is a mistake on the TS website. 

The CC has better contrast and will take a lot more magification than either the SCT or MAK. My 8” CC gives better views than my 10” dob for lunar. Also the build quality is better than the SCT or MAK. Had someone take a look at the CC and he was impressed by the build quality and he owns a Tak Mewlon.

Yes it certainly can perforn on DSOs but it’s on lunar / plaetary where it is something special.

Interesting. Can you post / link to proof of the "99 per cent Dielectric" claim by TS being wrong?

Regards

[johninderby]

Simple. The scope is made by GSO. and GSO says the reflectivity is 96%.

[vlaiv]

45 minutes ago, johninderby said:

Simple. The scope is made by GSO. and GSO says the reflectivity is 96%.

Not sure if that is anything conclusive as GSO makes these scopes for those who order them under their own brand - like TS, Altair Astro and iOptron.

Maybe they have options when ordering batch of scopes - "please tick box next to wanted mirror coating type a) 96% b) 99%"

 

[Live_Steam_Mad]

If anyone gets a chance to compare the TS 8" CC with a C8 XLT or Meade 8" UHTC (SCT/ACF) side by side at the same magnification, I would love to hear what the brightness difference is, as I am interested in buying this scope for the return of Mars later this year, I was hoping that it the 8" CC would outperform my Meade 7" Mak (which has the best corrected and smoothest optics of any scope I ever tested) and my rough, primary misaligned and overcorrected C11 and my rough SkyWatcher 8" F8 Newt which has some Spherical Aberration.

If Meade product designers ever read this, please bring us an 8" version of your 7" Mak, it was wonderful.

Regards.

[Greymouser]

Got to admit I found these very tempting after reading the thread by @johninderby, but would probably consider the 6" version, ( the price is superb... ) certainly at first, but even that is a good twice the weight of my little C5 which puts me off a little bit, it is even heavier than the C6. Of course if it proved to be much better, I would then probably get the 8" to replace my C9.25. Perhaps, but the 9.25 is very good. For my needs, it is a shame they do not do an even smaller one for that added mobility. I don't suppose anyone knows of anyone who does an even smaller one?

I guess there are worse problems to have, than worrying about which astronomy direction to go in next eh?