New GSO Classical Cassegrains

[Charles Kirk]

On 03/01/2020 at 11:10, johninderby said:

Some interesting info on the CC vs RC.

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

Am I correct in assuming that the spot analysis is for the edge of a 2.0 inch (50mm) field for 20 inch RC and CC apertures?

The analysis is very interesting and probably explains why they went for the CC design at f/12 instead of an f/12 RC design, the CC design being slightly easier to build.

I don't understand the effective aperture discussion in the CN review

https://www.cloudynights.com/articles/cat/user-reviews/telescopes/gso-8-inch-true-cassegrain-r3215

Using a smaller secondary will increase the contrast of fine planetary detail and reduce the fully illuminated field diameter which the review states is  100% over a 15mm diamater, but the effective aperture is going to be similar to that of a Celestron 8 Edge as they both have central obstructions of similar size. I wonder if the lower image brightness in the CC was one or both of higher magnification and a smaller fully illuminated field diameter .

Edited January 8, 2020 by Charles Kirk

[vlaiv]

3 hours ago, Charles Kirk said:

I don't understand the effective aperture discussion in the CN review

It just does not make sense to me.

If there is fully illuminated part of the field - let that be 15mm diameter - then any aperture stop needs to be on primary mirror itself - and there does not seem to be any. Any aperture stop that happens after primary mirror will be at some distance from focal plane and will impact field illumination - but if you have piece of fully illuminated field - then that light reaching that part of field is not stopped down - thus saying that mirror size is effectively 7.4" and there is 15mm of fully illuminated field - simply does not makes sense.

[nfotis]

So, the question becomes: Skymax 180 or CC8? 

Having f/12 instead of f/15 and an open tube (fewer acclimation delays) seem to be the main advantages (and a good dual speed focuser) for the GSO (I suppose that these are the same quality as the TS units).

On paper, the main advantage of the Skymax 180 seems to be a slightly longer focal distance (not a huge difference). And no diffraction spikes due to the spider vanes.

What's the visual and imaging quality, though? I haven't seen many examples in Astrobin by both types.

 

N.F.

 

 

[johninderby]

Visually it’s no contest. The CC8 is the clear winner. Shows more detail and will take higher magnification which I assume is partly due to the bigger aperture.. I liked my Skymax180 when I had it but it is outclassed by the CC. No way would I go back to the 180 mak.Like the CCs quicker cool down and lack of dewing problems.

I upgraded the focuser to a Baader Steeltrack with a much greater drawtube travel so don’t need to use the focuser extentions. 

I see TS is now stocking a 10” truss tube version of the CC. 🤔

Edited September 16, 2020 by johninderby

[Macavity]

On 08/01/2020 at 19:44, vlaiv said:

It just does not make sense to me.

"Who knows"? Perhaps best (for me) not to go there! There have always been
a lot of Mak Dissenters... "Planetary only scopes" etc. But I spent quite a while
pondering SW MAK127 / 150  FoV's... Hard vignetting... Soft vignetting etc. 🙃



The rays diverge outwards after passing through the meniscus? The (thicker)
OTA (does) stops down the tube? I sensed that most of *vignetting* was due
to the "baffle" tube along which the mirror travels... But without ray tracing? 🤔

The MAK127 is know to provide (at least visually) a usefully wider field than
the complete pessimists suggested? I did note you could shine a BRIGHT
white LED torch though the secondary mirrors! But idem "10**5" Solar Film... 😉

Edited September 16, 2020 by Macavity

[johninderby]

I love my little Bresser 100 grab’n’go mak. Gives great views in a small package.  🙂

Edited September 16, 2020 by johninderby

[quigley]

Update: I sold my 8" GSO CC. It has been known for a while that GSO did optical adjustments on these rendering a rather 7.3" aperture compared to the 200mm or 8" advertised. I compared this to an vintage C8 without special coatings dated 1976 and the C8 image was brighter and while giving the nod to the GSO for higher resolution, sold it. I have kept the 6" GSO CC because it functions as a true 150mm scope and has ultra sharp optics that outperform an 8" SCT resolution wise. I was disappointed with the nameless dealer who insisted that an 8" is an 8", is an 8". Obviously jaded toward selling GSOs. On another note, perhaps not the right forum but I also had a GSO 8" f:5 newt. I needed a coma corrector for that to achieve marginal coma with SWA and UWA eyepieces. I just purchased an Orion XX12i f:4.9, expecting to see coma...did not! Whatever Orion's owner Synta did with the optics in the 12" truss tube model at least, are he finest optics I have looked through in that aperture! No coma even with the Ultra wides...so I have a GSO coma corrector for sale on CL and FB Marketplace now....

[quigley]

Some time ago I posted a relatively stellar review of the GSO Classical Cassegrains as well as their 8" f:5 reflector. I also posted a brief on the information I found out about these scopes. Here I want to expand a bit.

I have had two years to further evaluate these mechanical gems. And, mechanically they are a lot for the money with quality build and 10:1 Crayford focusers standard. My initial reaction was one of the high reflectivity and lack of a corrector, thus making these far superior to SCTs including the fact that there is no image shift with the focusers on these scopes and a fixed primary. However....while I will give them credit for mechanical superiority to some other scopes. This is the REAL facts that came forth after using them for a while and comparing them with other scopes I acquired since the GSOs. The CCs do give incredible resolution, no doubt about that given an f:12. HOWEVER, THEY DO NOT OPERATE AT THE APERTURES ADVERTISED! This is NOT a 6" and an 8" and due to the design operate more on a 5.4" and 7.4" aperture. Comparing these to an older 1976 Celestron SCT confirms that the 8" CC is no match for it in light gathering power and the design 'flaw' is just as apparent in the 6" CC when compared to a Celestron 6" XLT SCT. Not as bright. The secondary and primary system may measure the distance but the primary does not yield the full aperture advertised. I sold both of mine and never looked back! My recommendation, skip the 6" GSO CC completely. If you're happy with a 7" CC advertised as an 8" with superb views of the moon and planets and not deep sky objects then that's up to you. I didn't like the compromise, nor the primary seller of these either and there are a couple. They are cloned by several dealers so if it's a 6" or 8" CC f:12, it's a GSO made by Guan Sheng Optical (GSO) and it shares the same 'disability.'

Another scope is plagued by the same optical limitations and it comes in the form of the 127 f:12.x MAKS, any brand since they all come from Synta. They claim to be a 5" but again, due to the same optical flaws it really only functions as a 4.4" MAK. I know this to be true since I have a 4" MAK, same 'brand' Orion and compared them on M13 one night and expected a noticable difference between 102mm and 127mm. Not so. The 127mm that really operates at about 114mm was only slightly brighter, difficult to discern the difference at all.

Now on to the GSO 8" f:5 reflector. Again, mechanically outstandingly built same sort of Crayford 10:1 and I expected the optics to be great given the specs from high reflectivity and specs from GSO's primary seller. NOT SO! I have owned a number of 8" f:4.9/f:5 reflectors from Orion, Cave and others. Most did not have sufficient coma to even require a coma corrector. The GSO HAD to have a coma corrector and even with one made by GSO there was a tremendous amount of coma in the eyepieces. Even those of moderate 60 degree AFoV. I never considered any light gathering limitations only because the coma was so bad that it wasn't worth using. That was sold as well. Another word of caution in general on the GSO reflectors, the tube rings are very tight. I had a 6" f:5 where the hinge on the rings was unprotected and badly scratched and dented the tube. I discovered it after the 30 day return period had expired and the major seller of GSOs made me pay the return shipping even though it was a manufacturing defect and they knew it. 'Very bad!

I have had quality issues with some of the Sytna products but when Orion's truss tube 12" XX12i was available a year ago, late spring 2021, I bought one. I wanted the Object Locator and the 12" optics. I felt for sure that I'd have coma in such a short focal length rich field telescope. However, I must have gotten a needle in a haystack because when I hit dark skies I put in the GSO coma corrector and it had too much out-travel to focus and I figured for certain that I'd have a lot of coma. NOT! No coma even using Meade's 5000 UWA 82 degree AFoV eyepieces! I was truly amazed! And it didn't stop there. The scope of that focal length and design isn't supposed to be a planetary wonder. Seeing the Encke Division at 400x made me think again! It performs like a 12" f:8 or better with the finest optical balance I've ever encountered in a scope this size. Put in a Lumicon 2" UHC filter and nebulosity abounds. And the Object Locator, the easiest manual GoTo I've ever had the pleasure to use. Bortle 2 dark skies yielded the central star in M57 - visually!

However...that's an aside. Needless to say the GSO scopes aren't what they seem and neither is the 127 MAK, your choice of brand..they are all the same if made by Synta. The information on the GSOs as well as the limitations on the 127 MAKs are all well documented on CN...

[johninderby]

Love my 8” CC and impressed with the views as are many using it and don’t give a damm about the reduced aperture as the scope is still an exceptional performer.

It’s the views through the scope that counts. Had a Celestron C8 and much prefer the CC8”

 

Edited March 18, 2022 by johninderby

[neil phillips]

On 18/03/2022 at 18:05, quigley said:

Some time ago I posted a relatively stellar review of the GSO Classical Cassegrains as well as their 8" f:5 reflector. I also posted a brief on the information I found out about these scopes. Here I want to expand a bit.

I have had two years to further evaluate these mechanical gems. And, mechanically they are a lot for the money with quality build and 10:1 Crayford focusers standard. My initial reaction was one of the high reflectivity and lack of a corrector, thus making these far superior to SCTs including the fact that there is no image shift with the focusers on these scopes and a fixed primary. However....while I will give them credit for mechanical superiority to some other scopes. This is the REAL facts that came forth after using them for a while and comparing them with other scopes I acquired since the GSOs. The CCs do give incredible resolution, no doubt about that given an f:12. HOWEVER, THEY DO NOT OPERATE AT THE APERTURES ADVERTISED! This is NOT a 6" and an 8" and due to the design operate more on a 5.4" and 7.4" aperture. Comparing these to an older 1976 Celestron SCT confirms that the 8" CC is no match for it in light gathering power and the design 'flaw' is just as apparent in the 6" CC when compared to a Celestron 6" XLT SCT. Not as bright. The secondary and primary system may measure the distance but the primary does not yield the full aperture advertised. I sold both of mine and never looked back! My recommendation, skip the 6" GSO CC completely. If you're happy with a 7" CC advertised as an 8" with superb views of the moon and planets and not deep sky objects then that's up to you. I didn't like the compromise, nor the primary seller of these either and there are a couple. They are cloned by several dealers so if it's a 6" or 8" CC f:12, it's a GSO made by Guan Sheng Optical (GSO) and it shares the same 'disability.'

Another scope is plagued by the same optical limitations and it comes in the form of the 127 f:12.x MAKS, any brand since they all come from Synta. They claim to be a 5" but again, due to the same optical flaws it really only functions as a 4.4" MAK. I know this to be true since I have a 4" MAK, same 'brand' Orion and compared them on M13 one night and expected a noticable difference between 102mm and 127mm. Not so. The 127mm that really operates at about 114mm was only slightly brighter, difficult to discern the difference at all.

Now on to the GSO 8" f:5 reflector. Again, mechanically outstandingly built same sort of Crayford 10:1 and I expected the optics to be great given the specs from high reflectivity and specs from GSO's primary seller. NOT SO! I have owned a number of 8" f:4.9/f:5 reflectors from Orion, Cave and others. Most did not have sufficient coma to even require a coma corrector. The GSO HAD to have a coma corrector and even with one made by GSO there was a tremendous amount of coma in the eyepieces. Even those of moderate 60 degree AFoV. I never considered any light gathering limitations only because the coma was so bad that it wasn't worth using. That was sold as well. Another word of caution in general on the GSO reflectors, the tube rings are very tight. I had a 6" f:5 where the hinge on the rings was unprotected and badly scratched and dented the tube. I discovered it after the 30 day return period had expired and the major seller of GSOs made me pay the return shipping even though it was a manufacturing defect and they knew it. 'Very bad!

I have had quality issues with some of the Sytna products but when Orion's truss tube 12" XX12i was available a year ago, late spring 2021, I bought one. I wanted the Object Locator and the 12" optics. I felt for sure that I'd have coma in such a short focal length rich field telescope. However, I must have gotten a needle in a haystack because when I hit dark skies I put in the GSO coma corrector and it had too much out-travel to focus and I figured for certain that I'd have a lot of coma. NOT! No coma even using Meade's 5000 UWA 82 degree AFoV eyepieces! I was truly amazed! And it didn't stop there. The scope of that focal length and design isn't supposed to be a planetary wonder. Seeing the Encke Division at 400x made me think again! It performs like a 12" f:8 or better with the finest optical balance I've ever encountered in a scope this size. Put in a Lumicon 2" UHC filter and nebulosity abounds. And the Object Locator, the easiest manual GoTo I've ever had the pleasure to use. Bortle 2 dark skies yielded the central star in M57 - visually!

However...that's an aside. Needless to say the GSO scopes aren't what they seem and neither is the 127 MAK, your choice of brand..they are all the same if made by Synta. The information on the GSOs as well as the limitations on the 127 MAKs are all well documented on CN...

Well 7.4 is good its bigger than i thought. I thought it was 7.3. Yes a 8" SCT may well be brighter. But the CCs are not really for deepsky, most planets and the moon are bright. So working at 7.4 rather than 8" isnt really a huge problem. If you got the scope for lunar and planetary. Which considering its design. Is likely. You mention a few of the positives. Then concentrate on the downside. Which as mentioned is actually not that major. I would recommend the scope to people who may be in the market for a 7" Mak. which isnt 7" either so as a alternative to that its brighter. Each to there own if that slight drop in brightness bothered you that much. Then you did the right thing for you i guess. I love mine. Ive seen it outperform a C9.25 on the same night on lunar imaging over at CN. which is considerably larger.  I would pit my scope against any 8" SCT imaging the moon in the UK I believe it would have the advantage. All scopes are a compromise. And the CCs are no exception. Both CCs and SCTs are great scopes. With different strengths and weaknesses. 

[johninderby]

What’s that old saying “Horses for courses”🤔

[neil phillips]

2 hours ago, johninderby said:

What’s that old saying “Horses for courses”🤔

I dont have to whip mine. It runs alright 🤣