Review of the GSO 6" f/12 Classical Cassegrain - How Does the "Class Cass" Perform?

About $600 USD, depending on where you buy it.
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[@MrBonger88]

Thanks Ed. Great video. I’m always learning something new from your reviews

[@bobbya8622]

Always enjoy your reviews, especially when you include images! Thanks for this review. I am wanting to add a Cassegrain, and CC is becoming appealing to me, particularly the Orion version, although the Celestron Nexstar 6SE or 8SE SC’s are very appealing also.

[@michaelklemm-abraham7298]

Dear Ed, I have one of those. It is a great telescope but in many ways you are correct: I currently have three scopes in use, this is the third of those three I bought. My other two are a 200/1000 newtonian and a 80/600 apo. Both used for astrophotography. The Cassegrain I bought for visual and planetary photography. There is also a 0.67x reducer available that works on the Cassegrain as well as the RC variant that is available with a faster f-ratio. With the reducer it gets way better for DSO imaging. Also, I only use APS-C and M4/3 size sensors so I have no issues with sensor coverage. Best, Michael

[@johndrummond3697]

Ed seems to be a very clear and detailed presenter. Very well done!

[@johnhoward6201]

Great review very helpful, with lots of interesting general points and not restricted to the Classical Cassegrain. Reviews of mounts would be great, especially SkyWatcher SkyTee 2, EQ5 Pro and HEQ5 Pro, or Celestron equivalents.

[@endautrestermes]

Thanks for the review, Ed. I would love to see you reviewing mounting options, just as I heard you speaking about paying too much attention to OTA indeed. Cheers !

[@LiquidAudio]

Another excellent review, thanks Ed!

[@mudlee1058]

I bought one in January. Sold it a week ago. It’s like a hell to collimate. You can only do it properly by your eyes, laser does not work properly. Also, the way how to collimate depends who you talk to. The focuser must be without any optical elementa, but the secondary with the 90 diagonal. When you think you are done with the collimation, if you rotate the focuser, then it’s done. You must start over. Once you collimated 100%, it’s a perfect scope. Till you change anything in the optical line. I could never collimate it to 100%, I managed to do a 95% approx. Almost all night went for setting it up, instead of observing. I do only recommend this to people who really know what they are buying.

[@edufau815]

Very interesting tip... I think this warning can also be part of Mr. Ting's very quietly enthusiastic review...

[@RT65CB-SWL]

Hi Ed. Excellent video👍. I do like catadioptric 'scopes😜 Also agree about the plastic backend of the Meade ETX [Maksutov] series. I had an minor accident😣 with my 'de-forked' 105 several years back and got a local engineering workshop to make a replacement backplate for it. Luckily the impact did not or only caused a minor shift in collimation, as it fell in long grass which helped cushion the impact. The only snag is that I have attached the dovetail bar to the OTA with some padded 'Jubilee' / hose rings so I can attach it to my Tele-Optic Giro or AOK-AYO alt/ax mounts, as I cannot find any tube rings that are the same diameter [about 124mm]... the nearest I have seen are about 125mm🤔.

[@johnhoward6201]

The daylight comparison of the telescopes was really very helpful, it would be great if you could use this technique with other scopes. Resolution, contrast, distortion, and CA were all readily apparent. Brilliant !

[@solarscopedunedin3853]

I like this test too but I don't think the CC6 is any less sharp there than the C6 - especially once you allow for the CC's larger image scale and ignore the different illumination. Combined with the flatter field, the CC does the better job here, at least to my eyes.

[@briankotak403]

Great video Ed. I have a 51mm and 110 mm aperture refractor but have been looking at higher focal length scopes for planetary and small DSO imaging. Thinking about a 8” Edge (and the 0.7x reducer) but also the Orion 8” classical cassegrain. I am leaning towards the Edge, as collimating the CC scares me a bit. Seems like a lot of people have difficulties in achieving and maintaining collimating of CCs and RCs. Best wishes. Dr B from Manitoba, Canada 🇨🇦

[@ohwell2790]

I have the Orion 150 mm classical cassegrain and have a heck of a time with collimation. Actually prefer my Orion 120 mm short tube refractor, but I keep trying anyway. Bought it because of your review and really like it, use it with a minus violet filter and stars look just fine.

[@stevehanson5556]

Great information thank you Ed

[@KingLoopie1]

Nice balanced review for these low end scopes. I did notice, that the classical cass had a more pleasing natural color due to the mirror system. At least on my phone's screen... Maybe this was just exposure and lighting? 👍

[@anorup]

Great review! Of course you can better judge the quality from the original images, but my quick impression from your daylight test was that the GSO CC actually provided the sharpest images, but with low contrast, as if there is a straylight issue. Maybe the sky is directly visible from the focal plane, looking beyond the edge of the small secondary mirror?

[@rebsredone450]

Thanks for the video Ed. Talking about lens covers that fall off. My new Celestron C6 has similar issues. The lid isn’t cheaply made, but it does not generate enough friction to stay on. Three dots of hot glue took care of that issue.

[@edting]

Mine does that too! I used sticky-backed felt to shim up my C6 cover.

[@rebsredone450]

@@edting You might be interested in this: I just told my wife that you had replied to a post of mine. She said: Tell him I think he is really smart and his style of presentation is really, really good!

[@ishanr8697]

Seems like a great budget alternative to a Newtonian if you want to use an EQ mount. If I had a bit of money and wanted to do compact planetary or close-up lunar, I'd go Mak-150 on an EQ5. Closed tube, meniscus corrector, small obstruction. If I wanted to spend a lot to get deep-field DSO and high-res lunar / planetary imaging, I'd probably go with a 9.25 Edge HD on an EQ-6 Pro. If money, size, space and weight were no object, I'd get an RC500, an EQ8 and a roll-off roof.

[@robi4514]

A great video Ed, thanks, very interesting to hear your views, particularly on the quality of the optics. One thing you didn’t mention (I think?) is the CC6’s lack of a corrector means it doesn’t dew up nearly so readily and no dew shield or heater is required most of the time (in my experience of owning an RC6 for imaging, I use a C8 for visual). That’s a big plus in my book, but perhaps less so for others. Thanks again for a great review and keep up the good work. 🙂

[@Astronurd]

It’s an easy job to fix the mirror shift on your ETX. Garnett Leary on KZbin made a video showing the procedure

[@Muesli711]

Thanks for the video. I don't think the price difference is so pronounced in the US but here in Germany, I checked the latest prices: 6'' CC: € 498 6'' SCT: € 985

[@edting]

Wow, the 6" SCT costs a lot where you live! I've heard similar stories about pricing in Europe.

[@arandomdude7391]

I've been eyeballing a few models as my next scope, I currently have a c90. One of the most appealing features of a CC is the lack of a large corrector plate, therefore I have less to fear of breaking during shipping (all the way to Central America). Is there any sights of stray light making it's way to the sensor/eyepiece?

[@skygazerII]

Just ordered your book, I hope to get it by Monday!

[@edting]

Thank you so much!

[@skygazerII]

@@edtingJust finished your book, a good read! Targeted information, laid out clearly, no fluff. I wish I'd had this book five years ago, when I started getting into astrophotography.

[@AmatureAstronomer]

Never heard of these before this video.

[@Astronurd]

Another great video Ed👍. I was contemplating buying the 8” model of this scope in the UK. My other choice was a C8 but I’ve heard several folk saying that they encountered mirror slip when focusing. What has your personal experience been using the C8?

[@brentjablonski3730]

Galileo: Ed is outstanding in his field! Simplicio: That's not his field he's standing in. Galileo: Well, his videos are still great, wherever he chooses to stand.

[@MountainFisher]

The Orion Star Blast is still available from $420 to $480. I do not know how good that one sided Dobsonian mount is. You mention the Celestron C6 and I just bought a C6-N f5 OTA reflector new in the box. I collimated it using a Cheshire and then double checked with a Laser collimator and Wow! I couldn't be happier views are clear to the edges with no discernable coma. I'm using a tripod and with a mount that's too light for it while I build a Dobsonian for it using that 8 1/4" Vixen base.

[@edting]

It's still $269 on the Orion web site. Check their "clearance" section also for possible deals.

[@engelhorns]

I have a Meade LX85, 5" refractor. I know they are no longer in production but could you do a review of them? I am looking at a Celestron 6" SCT and could really use a good comparison and will the LX85 mount handle the SCT.

[@BerrieBadslof]

Great review thanks! Can you tell me something about your exposure/gan settings for the Orion Nebula photo? I am struggling so hard to get this right. Thanks in advance.

[@edting]

HuTech modded EOS 5D Mk3, 30 X 25 second exposures at ISO 1600 stacked with darks, processed in PixInsight. Keep in mind if you don't have my equipment or software the numbers don't translate. I don't think that Orion Nebula image is all that great, nor is this scope very good for deep sky imaging in general.

[@hyperboogie]

Just seeing this now. A great review as always Ed 👍 Out of curiosity, why is this scope heavier than a sct even though it has no corrector plate?

[@edting]

The Class Cass is overbuilt. Normally I like this, but this thing is probably too heavy for its own good.

[@kingdavidcoffee]

Nice review but as you’re speaking I continually change my gaze and look at the Portaball behind you. I wish I had kept mine.

[@edting]

I remember your Portaball!

[@darkwood777]

I would love to find a source for hyperbolic secondary mirrors. Mine was damaged and all I can find are custom labs were the wait time is several years.

[@edting]

Sadly, in today's disposable economy, the cheapest solution may be to get another telescope.

[@mycarolinaskies]

Thanks Ed for the insight on the CC6. Honestly I'm non-plussed with smaller CCs having any relevancy other than no mirror shift vs an SCT or Mak of similar aperture if they aren't fitted with an external focuser. The lunar images didn't impress nor the terrestrial lackluster performance. Sure it's nice to have a large focal plane if shooting with a Full frame camera, but even with a corrector is it really 'superior' to the alternatives? I think not. Visually there isn't a compelling reason to buy a 6" CC as it isn't the superior viewing telescope. I think Ed hits it on the head, those buying a 6"(or 8" for that matter) simply are doing it more out of curiosity or some specific criteria in their collection. Most forum threads on the CC6 & CC8 GSO and similar are loaded with similar results to Ed's as well as a large percentage having rid themselves of these smaller versions.

[@tuunaes]

Non-catadioptric Cassegrains have far lower vulnerability to dew/frost than SCT (or Mak/MCT) which can be very big ease of use factor in many climates. Very exposed corrector is simply dew magnet needing mitigating measures.

[@daddyzac62]

Great video as always I own the GSO 6 inch RC. Will you review that scope also?

[@edting]

Every person I've talked to who owns one of those RCs has the same concern - collimation. If yours came perfectly collimated from the factory you won the lottery. Don't touch it. If yours isn't collimated you may be in for a long frustrating haul.

[@alcosound]

RCs are a specialized scope (more about photography). The GSO RC6 and RC8 are a bear to collimate accurately, due to the focuser construction as far as I understand. This guide might be helpful, though: www.dropbox.com/s/avpu2vn6s3ynsz5/Collimating%20GSO%20Ritchey%20Chretien%20with%20a%20plastic%20disc%20V2.pdf?dl=0

[@keithsmith8062]

@@edting I have an Apertura 8RC showing up tomorrow and I was just searching your channel for any thoughts on Ritchey-Chretien because after some research I had the same concern. But I am doing mostly astrophotography and I liked the Idea of having the normal Crayford Focuser like my SV503. Also No Corrector Plate at front to dew/Fog up. Have gotten lots of great info from your channel. Thank You so much. I'm not going to fret. Its just another skill to learn. I hope I hit the lottery also because the Saturn is nice and high right now, and I rather practice collimation after that at least. Clear Sky's

[@claws58]

Hi Ed! Which scope would you choose? The Orion SkyLine 10" Dobsonian Reflector Telescope or the Sky-Watcher Classic 250 Dobsonian 10-inch telescope? Thanks

[@edting]

At this point, take anything that's in stock. They are very similar. There are minor issues (the SW has those side handles that you can bump into in the dark, and I don't like the Orion's roller bearing azimuth system) but nothing's perfect and those things may not bother you.

[@andrewpitt9994]

Hi Ed - thank you for your channel, love your presentation style and content. I have a question please? I'm considering a new scope to view planets, specifically mars. I'm strictly visual for now and wonder which of the two scope you'd recommend as you've reviewed both. 1) 6 inch classical cassegrain (I'm looking at the Orion model) or the skywatcher 100ED. My preference is for a grab and go arrangement , what would you recommend? For context I have an 80mm F11, a ST80 and the Orion 120 short scope (based on another of your reviews) Thanks Andy

[@edting]

If you've looked at Mars through your existing scopes, you know it's not very interesting. A better scope won't do much more. Based on your current collection, you are seriously in need of an 8" Dob. I'd get one.

[@andrewpitt9994]

@@edting thank you for the fast response and your suggestion - I kinda wondered if you'd recommend the dob or something else. I'll take your advice and no doubt be grateful when it arrives. Best Andy

[@schmetterling4477]

@@andrewpitt9994 The only telescope that will make Mars look interesting is the camera on a Mars orbiter. If that is what you want to do with your life, it's probably time to get a job at JPL.

[@gowrissshanker9109]

Sir, Is it ok to use Monocular than to use binular in the beginning of studying about astronomy??

[@edting]

Most monoculars are awful. Stick with binos.

[@alcosound]

Would like to read a test of the eight inches version, it may be a useful planetary scope?

[@solarscopedunedin3853]

There is one in the Articles & Reviews section of the Cloudy Nights forum

[@Neanderthal75]

I recently bought a GSO RC6", which looks exactly like that telescope, but of course it has both mirrors hyperbolic. While collimation can be a either a nightmare or at least a challenge to even the more experienced astronomer, my bigger dilemma is that I have a 127mm Maksutov and also a 150mm Newtonian. I wanted a bit more magnification and I was just curious about Ritchey Chreiten, since I never owned one. I was hoping that it fills in as my med-high power telescope at 1350mm focal length, but its strange to see that my Maksutov could nearly match its performance and it's in the same price range. I imaged and did my visual visits with both scopes now, and I hate to say, but while the Mak may gives me a slightly softer look and a bit slower , it's ease of use, zero maintenance and grab-n-go capability outmatches the 3x heavier RC. I keep getting reminded about the old saying, that the best telescope is the one I will use the most often and by just looking at the scopes in the storage, I'm gravitated towards the Mak, for the reasons above.

[@ishanr8697]

I've never used a Mak, but I also hear them get praised left, right and center. I don't think they can be beaten if you aren't super worried about the extra weight of having a meniscus lens and don't need a huge aperture.

[@alcosound]

RCs are a specialized scope (more about photography). The RC6 and RC8 are a bear to collimate accurately, due to the focuser construction as far as I understand. This guide might be helpful, though: www.dropbox.com/s/avpu2vn6s3ynsz5/Collimating%20GSO%20Ritchey%20Chretien%20with%20a%20plastic%20disc%20V2.pdf?dl=0

[@alcosound]

@@ishanr8697 the Skymax 127 and 150 are very nice, but the largest one (the Skymax 180) is termed a "planet killer" thanks to its 2700mm focal distance. You need a steady mount, though, and probably an external focuser in order to avoid mirror flop

[@ishanr8697]

@@alcosound Believe it or not, I got myself a tiny little 60 mm Mak as a genuine " grab and go, throw in a backpack" scope to compliment my 305 mm Dob.

[@astrodojo1]

On spot, I'm not new to the hobby, not my first rodeo, I might leave it on the shelf and the reason is the low mount count to use it, I would rather use the mount to do some AP due to clear skies are scarce, but what I really don't get is that you are not impressed with it. So I'm less convinced now. Are you still leaving the 8" dobsonian to take it's place. So I'm in between an 8" CC or a 8" or 10" dobsonian, I f you could answer this would be much appreciated.

[@solarscopedunedin3853]

If you plan to do anything visual while the AP rig does its thing, get the 8" dob, no question. I have the GSO CC8 and also their 8" dob. The CC is a specialised high-power instrument. I haven't compared the two directly yet but I suspect its planetary performance is actually a tad better than the dob's. But the dob is much more versatile overall. It gets used all the time. The CC only come sout when conditions are great.

[@gowrissshanker9109]

Sir, Is 20*80 binacular suitable for beginners in astronomy? Thank you sir 🌟

[@edting]

Your issue isn't the binoculars, it's the mount. 20X80 binos are big and heavy and you aren't going to be able to handhold them. Shop the mount first and be sure they can hold such large binoculars. Also, be aware that binos become uncomfortable on your neck as you look upwards.

[@brodymk45]

did you ever do a review on the Sky-Watcher 102mm f/13 Maksutov-Cassegrain Telescope

[@edting]

All the Chinese-sourced Maks are the same. Decent value for the money, some QC issues. The bigger issue is the mount. Experience shows beginners almost always underestimate the size of the mount necessary to hold these long focal length optical tubes. As a result we are seeing an epidemic of undermounted Maks out there.

[@taraswertelecki9586]

@@edting I have a 90mm Orion 90mm Mak, and believe it or not I use to it to on my AVX mount which is more than steady enough for it. Even for the 8-inch Celestron EdgeHD SCT that mount supports it steadily, especially with the vibration suppression pads. As for the Mak, it's quite good from what I can see.

[@MiguelAriasS]

Is there an amateur Infrared (or near infrared) Astronomy?

[@solarscopedunedin3853]

Yes.

[@Python_Knows]

Would you ever consider doing a review on the celestron astromaster 130 EQ.

[@edting]

Junk. In the same category as the PowerSeeker 127.

[@Python_Knows]

@@edting thanks.

[@stefan-alexandruszakacs694]

Hello sir , I’m new and ready to make my first order , is Omegon a good choice ? I’m looking at Omegon Telescop Dobson Advanced N 203/1200 , may I please have an answer ? 🙏love all your videos , peace be with you

[@edting]

Yes, that is the class of telescope I've been recommending for 20+ years. We call them 8" Dobs here in the US. If you can find one in stock, grab one.

[@stefan-alexandruszakacs694]

@@edting astroshop is a realiable website ?

[@edting]

I can't say, as I don't know about the retailers outside the US.

[@GaryMCurran]

Ed, could you respond with the differences between a 6" Classical Cassegrain and my GSO 6" R.C.? Other than the focal length being longer, and I would assume the tube is longer and the mirrors configured for that, I don't really see a difference.

[@edting]

It all depends on the state of collimation in your RC. Every RC owner I've talked to complains about it. A classical cassegrain isn't too bad to collimate but and RC can be an ever-spiraling nightmare if you get it wrong. The RC is thought by some to be the ideal telescope because it is suitable for visual and photographic use (they are usually faster than CCs and Maks).

[@Astrofrank]

@@edting But don't forget the high obstruction of the RC - the common 50% will reduce contrast far more than the about 38% of the shown classical Cassegrain or the 37% to 40% of many SCTs.

[@alcosound]

These have different mirrors. The RC has both the primary and secondary mirrors as hyperbolic design, so any small change from the optimum collimation tends to depart the ideal area quickly. A Maksutov with spherical corrector and primary mirror is more "gentle" and easy to collimate. The Classical Cassegrain has a spherical/parabolic primary and a hyperbolic secondary mirror, so it's moderately hard to collimate correctly (I think that the focuser on the 6 and 8 inches RC versions acts on the primary mirror directly?)

[@edufau815]

@@Astrofrank I think the CO in the OSG CC is lower, around 33%

[@Astrofrank]

@@edufau815 You are right, only the 6" has 38%. Sorry!

[@mikenofi281]

Ed, The classical cas has baffles. Did you notice superior image contrast compared to the Celestron Cass 6 and Meade 5 Mak?

[@edting]

I didn't notice any difference in contrast between the three scopes. Nice to see those baffles in there though.

[@DavidEman]

Is there any chance for you to review the 8" model in the future? :)

[@edting]

The Chinese stuff within a particular line tends to be very similar. Scale up my comments on the 6” and you’ll get a good feel for what the 8” is like. Keep in mind you are going to need a very sturdy mount to hold that 8”.

[@DavidEman]

@@edting Thanks Ed. I've read it on various forums that these models dont really operate at full aperture. These reports usually state 138mm for the 6" and 187mm for the 8", which makes the actual obstruction (including the secondary baffle) larger. I believe its 44% for the 6" and 37% for the 8", thats why I was curious for your insight. The 44% CO would explain why the C6 is actually sharper than the 6" classical cass.

[@user-qe9ji7hj4w]

What is the difference between a classical Cassegrain and a Ritchey Chretien?

[@edting]

A Class Cass has a parabolic primary and a hyperbolic secondary. In an RC both mirrors are hyperbolic (good luck collimating your RC if it goes out).

[@MrLink-dk7yn]

Hey Ed, do you compose the music for your videos?

[@edting]

No, but you're giving me ideas....

[@MrLink-dk7yn]

@@edting I'm completely alien to the music business but a quick googling landed me to this yt vid kzbin.info/www/bejne/o2Haaomgecymh5I It's a hole new rabbit hole for sure!

[@trackdayadventures]

Do you think this would make a decent planetary imaging scope?

[@solarscopedunedin3853]

My 8" CC works great for planetary imaging. One feature of the CC that isn't mentioned in the video is that being a pure reflector, the lack of glass in the optical path means there is less to interfere with transmission, and being a Cassegrain, you can do high-power imaging at prime focus without adding glass back into the mix (barlows) with suitable sensors (the IMX178 is a great match for an f/12 optic). The combination of these two features is key. To visual-only observers this doesn't matter much, and explains why Maks are so highly regarded by some. However, this becomes a significant factor to consider should you choose to venture outside the visual spectrum, into UV and IR, which to me is part of the reason I use cameras in the first place.

[@trackdayadventures]

@@solarscopedunedin3853 Exact reasons why I am researching this scope. I am about to buy the Orion version to try out. I had a Mewlon 180 and it was about perfect but the lack of mounting options on it made me sell it. I didn't want to mess up a work of art by drilling mounting holes. It seemed perfect for my location and I didn't have to worry about dew like on my SCTs. GSO products seem very well made from the items I have owned

[@StereoSpace]

A Celestron CGEM will set you back around $1,800.

[@edting]

Yes, that's about right...

[@gowrissshanker9109]

Sir, Don't we have a Telescope that is powerful enough to see A FLAG IN MOON?... IF NOT HOW BIG THE TELESCOPE SHOULD BE TO SEE A FLAG IN MOON? THANK YOU SIR 🌟

[@MrAstrojensen]

More than 100 meters in diameter. No such telescope exist or will exist in the foreseeable future. Think about it: You're trying to see a small flag, more than 350000 kilometers away.

[@johnhoward6201]

The ELT currently under construction in Chile might see a very large flag on the moon as it is hoping to have a resolution of 0.005 arc sec.

[@edufau815]

Although visualizing the flag is theoretically possible with the ELT, let's remember that the optical resolution is a theoretical value only achievable outside the atmosphere. Active and adaptive optics systems bring the real value of resolution closer to the theoretical one, but I am afraid that it will not be reached even under the best seeing conditions, such as those that can occur in the Atacama desert... so I have doubts about that the famous little flag can be distinguished even with the future ELT.