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GSO 6inch F12 Classical Cassegrain It’s A Winner!

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#51 Stephen Kennedy

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Posted 20 April 2019 - 08:24 PM

I am not really sure what the point of bringing this classical Cassegrain to market when GSO is already selling an RC of the same aperture.  Ritchey and Cretien designed the RC for the sole purpose of correcting the optical abberations inherent in the CC and other reflectors with paraboloidal primary mirrors. 

 

It seems that GSO is the only company in the world to have figured out how to mass produce high quality hyperparaboloidal mirrors.  Maybe they just wanted another product that they could use the convex hyperbaraboloidal secondary in. 



#52 Mirzam

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Posted 21 April 2019 - 07:33 AM

RCs are photographic scopes. CCs are more oriented towards visual.  Differences in obstruction size, illuminated fov and off-axis correction.  Agree that the GSO optical fabrication has become pretty good.

 

JimC


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#53 terraclarke

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Posted 21 April 2019 - 12:07 PM

I am not really sure what the point of bringing this classical Cassegrain to market when GSO is already selling an RC of the same aperture.  Ritchey and Cretien designed the RC for the sole purpose of correcting the optical abberations inherent in the CC and other reflectors with paraboloidal primary mirrors. 

 

It seems that GSO is the only company in the world to have figured out how to mass produce high quality hyperparaboloidal mirrors.  Maybe they just wanted another product that they could use the convex hyperbaraboloidal secondary in. 

I think (and probably rightly so) that they have perceived a demand in the market for a visual Cassegrain scope; their RCs are primarily for AP and best used for non-visual imaging work and Mewlons and DKs from other vendors are much more expensive. That said, I think they figured, why not, as most of the parts and technology for assembly were already on the shelf, in house from making their other products, the RCs in particular. I also think that their reasoning hit a major snag during assembly and testing of their initial output and it wasn’t anywhere near the snap they might have thought it would be. Hence the delivery deadlines being delayed almost since the get go. I pre-ordered with Astronomics when the AT-branded ones were first announced a year or more ago and after several delays I cancelled my order. While I think it is a cool idea, in practicality I am far from getting one.


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#54 Phil Cowell

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Posted 21 April 2019 - 04:20 PM

I think (and probably rightly so) that they have perceived a demand in the market for a visual Cassegrain scope; their RCs are primarily for AP and best used for non-visual imaging work and Mewlons and DKs from other vendors are much more expensive. That said, I think they figured, why not, as most of the parts and technology for assembly were already on the shelf, in house from making their other products, the RCs in particular. I also think that their reasoning hit a major snag during assembly and testing of their initial output and it wasn’t anywhere near the snap they might have thought it would be. Hence the delivery deadlines being delayed almost since the get go. I pre-ordered with Astronomics when the AT-branded ones were first announced a year or more ago and after several delays I cancelled my order. While I think it is a cool idea, in practicality I am far from getting one.

A DK could be another possibility. 



#55 Mirzam

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Posted 21 April 2019 - 07:50 PM

As long as there is no moving primary mirror arrangement the DK is an OK option.  Lots of off-axis coma though.

 

JimC


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#56 Thandal

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Posted 22 April 2019 - 09:27 AM

I am not really sure what the point of bringing this classical Cassegrain to market when GSO is already selling an RC of the same aperture.  Ritchey and Cretien designed the RC for the sole purpose of correcting the optical abberations inherent in the CC and other reflectors with paraboloidal primary mirrors. 

 

It seems that GSO is the only company in the world to have figured out how to mass produce high quality hyperparaboloidal mirrors.  Maybe they just wanted another product that they could use the convex hyperbaraboloidal secondary in. 

 

 

RCs are photographic scopes. CCs are more oriented towards visual.  Differences in obstruction size, illuminated fov and off-axis correction.  Agree that the GSO optical fabrication has become pretty good.

 

JimC

 

 

I think (and probably rightly so) that they have perceived a demand in the market for a visual Cassegrain scope; their RCs are primarily for AP and best used for non-visual imaging work and Mewlons and DKs from other vendors are much more expensive. That said, I think they figured, why not, as most of the parts and technology for assembly were already on the shelf, in house from making their other products, the RCs in particular. I also think that their reasoning hit a major snag during assembly and testing of their initial output and it wasn’t anywhere near the snap they might have thought it would be. Hence the delivery deadlines being delayed almost since the get go. I pre-ordered with Astronomics when the AT-branded ones were first announced a year or more ago and after several delays I cancelled my order. While I think it is a cool idea, in practicality I am far from getting one.

 

I agree with both of the above responses to the question: at a price I was willing (able) to pay, a CC or mak-cass were the two best choices for my priorities, which are strictly visual planetary and lunar observing. I haven't seen anything close to f/12 in an affordable RC.  In fact, don't really see any RCs in my price-range at all.

 

I wrote a long post containing my Pros and Cons between the two, (see Post #33, this topic) and why I went with the CC, but if Orion isn't able to ship the CC by next month I may reevaluate.  There are, after all... "options".  wink.gif



#57 Stephen Kennedy

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Posted 22 April 2019 - 02:38 PM

I had forgotten how many mainly visual and Solar System observers there are and agree that the CC is probably a better choice than an RC is for that. I now think that GSO saw that a CC would appeal to mainly visual astronomers while the RC would be attractive to those who are primarily imagers.

My TPO RC6 which I ordered several months ago from OPT arrived in less than a week and appears to have been shipped directly to me from GSO in Taiwan. It arrived in perfect collimation and at F/9 is good for DSO imaging and can be used for Solar System visual observing. I agree with Terra that given GSO's solid experience with making RCs it is surprising that there is a delay in production of CCs. It could be that they found the CC harder to produce than they expected. The only thing I can think of is that the very fast (F/2 to F/3) paraboloidal mirror that a CC uses for a primary may have been more difficult to mass produce than anticipated. The hyperparaboloidal primary mirror in my RC6 seems to be an F/3.
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#58 macdonjh

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Posted 22 April 2019 - 09:24 PM

As long as there is no moving primary mirror arrangement the DK is an OK option.  Lots of off-axis coma though.

 

JimC

But a Dall- Kirkham wouldn't take advantage of the paraboloidal primary mirror required for a classical Cassegrain, which GSO already makes for the Newtonian scopes they sell; or the hyperboloidal secondary mirror required, which they also already make for their Ritchey- Cretien scopes.

 

Dall- Kirkham scopes don't have annoying coma if they are slow enough.  I haven't looked through a Robert Royce DK yet; he recommended f/18 or slower I think. Mewlons are f/12 and I think they are great.


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#59 memento

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Posted 23 April 2019 - 02:17 AM

If this scope would be f/18 or at least f/15, the secondary could be smaller. Also there need to be some compromises made so that you can attach 2“ eyepieces or binoviewers etc. hence there‘s that huge extension ring before the focuser (see photo in first posts in this thread).

But I get that at this price point there just is no r&d and production money for a more uncompromised design, so they went with this f/12 configuration and extension tube design.
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#60 DJAZ

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Posted 23 April 2019 - 08:30 AM

The classical Cassegrain has a heavy steel tube apparently instead of aluminum.

The classical Cassegrain will absolutely have cooling issues. A 4” refractor or an insulated Mak/SCT, not so much. The classical Cassegrain will cool faster than a non-insulated Mak/SCT. Keep in mind it cost me $14 and half an hour with a pair of scissors to insulate my Mak. Any modification that doesn’t require a screwdriver isn’t much of a modification in my book.

Note the CC6 has baffles. Read reports about Mewlons and see how that wreaks havoc on cooling time. Have to leave the tube pointed straight up for an hour or so to let the heat escape the baffles. And hope bats and birds don’t dive bomb the mirror. You really aren’t gaining a significant advantage in cooling time with a CC over a Mak/SCT, and you lose the ability to eliminate cooling time by insulating. Just saying. Not saying the CC is a bad scope. But just don’t buy it for fast cool down times.

Scott

Modern CC's are not constructed with heavy steel tubes anymore.  They're using carbon tubes and carbon trusses.  Really, think of a modern CC like a modern Newt or Dob this way.

 

Cooling is better with a CC.  I've owned both a CC and mutliple SCT's.  My CC runs circles around any of my past SCT's  Peak seeing post sunset - CFF350 vs C14HD - planetary imaging with both scopes.  My C14HD would be rendered useless with internal heat plumes for 3-4 hours - not the case with the CFF CC it's ready to use post sunset.  I might add, I don't live near the coast with low delta T's.  I live in the hot desert with 30-40 F delta T's so worst case.  And with a closed tube scope, you cannot do an adequate boundary layer air sweep.  As temps drop, with any reflector, you will need to get rid of these bad layers around the primary.  You cannot do this in a closed tube scope, well unless you modify it and open it up so that proper sweeping can occur.  (but they are not made this way out of the factory of course)

 

Birds and bat droppings...well I suppose but they could also bomb the corrector plate of an SCT or Mak.  I've had my CC open probably for 300 hours for the past 4 years for planetary imaging, no bombs yet.  But yes, I suppose there's a slim chance.

 

DJ



#61 DJAZ

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Posted 23 April 2019 - 08:32 AM

RCs are photographic scopes. CCs are more oriented towards visual.  Differences in obstruction size, illuminated fov and off-axis correction.  Agree that the GSO optical fabrication has become pretty good.

 

JimC

Really it depends on the imaging target.  DSO's or planetary, both on extreme ends of the spectrum so to speak.  DSO imaging, RC's all the way.  Planetary imaging, CC's all the way.

 

DJ



#62 terraclarke

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Posted 23 April 2019 - 11:57 AM

DJ: The steel tubes are for the 6” and 8” models so cool-down should not be as great a problem. The larger ones planned are said to be truss-tubes.

 

Thomas: I agree, I would have preferred something in the F15 to F20 range to minimize the size of the central obstruction, and I would think that the less deep curvature of the longer focal length primary would have been easier for them to make, and the smaller secondary would have been cheaper; so I am somewhat puzzled as to the F12 choice. My only guess is that the selected size conformed better with jigs and templates used with existing products, so they anticipated a quicker turnaround. Obviously tho, they ran into unanticipated problems during production. I am still vacillating on one of the 6”ers as I am just so dammed curious about them. 


Edited by terraclarke, 23 April 2019 - 11:59 AM.


#63 memento

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Posted 23 April 2019 - 01:06 PM

Yes terra, I was looking into those cheap Bresser 4“ achromats for some easy Moon and Planet watching but ultimately what’s the point of that when I already have a good 5” SCT at home.

Now adding another inch to that, and having an open system with only two mirrors, no corrector plate, all that from a company who apparently have a long record of getting the mirror surfaces right (in all their RC’s) ... got me curious.

I mean it’s a 399 Euro scope. That’s small money for any type of scope. So some compromises are okay. But as with anyone here who already has some other scopes, it’s still easy enough to say “no” ...

I’d be really interested in any reports of planetary observing, or maybe even a 1:1 to a 5-6” Mak or a 4” refrac... I do realize these things just start hitting the market so maybe I have to have some patience. We have a big astronomy fair coming up locally in May. Maybe I’ll jump for the 6” Cass if I see it there in person ...
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#64 Phil Cowell

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Posted 23 April 2019 - 10:11 PM

DJ: The steel tubes are for the 6” and 8” models so cool-down should not be as great a problem. The larger ones planned are said to be truss-tubes.

 

Thomas: I agree, I would have preferred something in the F15 to F20 range to minimize the size of the central obstruction, and I would think that the less deep curvature of the longer focal length primary would have been easier for them to make, and the smaller secondary would have been cheaper; so I am somewhat puzzled as to the F12 choice. My only guess is that the selected size conformed better with jigs and templates used with existing products, so they anticipated a quicker turnaround. Obviously tho, they ran into unanticipated problems during production. I am still vacillating on one of the 6”ers as I am just so dammed curious about them. 

The f12 keeps mount requirements down. The moment arm would be larger in the F15 to 20 range.


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#65 terraclarke

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Posted 24 April 2019 - 07:31 AM

The f12 keeps mount requirements down. The moment arm would be larger in the F15 to 20 range.

Yes, and it gets a bit wider field, but at the expense of the CO. At F12 it makes it more of an ‘all around’ instrument, but a CC is already sort of a specialized instrument, best suited for planetary and lunar viewing. I would have preferred it to be F15 with a smaller CO, but that’s just me and it’s admittedly a minor nitpick.


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#66 SeattleScott

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Posted 24 April 2019 - 10:39 AM

Modern CC's are not constructed with heavy steel tubes anymore. They're using carbon tubes and carbon trusses. Really, think of a modern CC like a modern Newt or Dob this way.

Cooling is better with a CC. I've owned both a CC and mutliple SCT's. My CC runs circles around any of my past SCT's Peak seeing post sunset - CFF350 vs C14HD - planetary imaging with both scopes. My C14HD would be rendered useless with internal heat plumes for 3-4 hours - not the case with the CFF CC it's ready to use post sunset. I might add, I don't live near the coast with low delta T's. I live in the hot desert with 30-40 F delta T's so worst case. And with a closed tube scope, you cannot do an adequate boundary layer air sweep. As temps drop, with any reflector, you will need to get rid of these bad layers around the primary. You cannot do this in a closed tube scope, well unless you modify it and open it up so that proper sweeping can occur. (but they are not made this way out of the factory of course)

Birds and bat droppings...well I suppose but they could also bomb the corrector plate of an SCT or Mak. I've had my CC open probably for 300 hours for the past 4 years for planetary imaging, no bombs yet. But yes, I suppose there's a slim chance.

DJ

These particular models have steel tubes. And they don’t have boundary layer fans. I suppose if you are handy and comfortable doing such mods, then the CC could have much faster cooling than a closed tube scope. To me, it is much easier to wrap a closed tube scope in Reflectix than cut a hole in a steel tube for a boundary layer fan. I understand the merits of your high end model with the carbon fiber and fans, but this model is not the same.

Scott

#67 doug mc

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Posted 24 April 2019 - 07:31 PM

I have not noticed cooling of my CC to be any more of a problem than what I had with my newt. A small fan placed near the front of the open tube before viewing has been recommended for the Tak open tube cassegrains. 



#68 SeattleScott

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Posted 24 April 2019 - 10:26 PM

Technically there probably isn’t a big difference in cooling time between the CC and a Newt. A newt probably doesn’t have baffles to trap heat and a Newt has a more open mirror cell that can better accommodate fans, so a Newt should cool somewhat faster. The real difference is most people use a newt for observing DSO which doesn’t require thermal equilibrium for satisfying views generally. Or at least you can start with low power stuff while the mirror cools. This CC is intended to be a more specialized lunar/planetary instrument, so cool down is more critical. Most people don’t pre-cool their Dob, but pre-cooling would probably be important for this scope, for the targets it is used for. That is where a closed tube Mak or SCT is advantageous in that you at least have the option of insulating them to deal with cool down. Not saying the CC doesn’t have other merits. Just saying don’t buy it for the faster cooling time.

Scott
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#69 Bomber Bob

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Posted 24 April 2019 - 10:41 PM

I was looking into those cheap Bresser 4“ achromats for some easy Moon and Planet watching but ultimately what’s the point of that when I already have a good 5” SCT at home.

 

Is your 5" SCT sharp at 70x / 80x per inch?  The Bresser AR-102L is.  My 1970s orange C5 Astro cruises at 300x, but the 1980s white-tube spotter topped-out at 50x per inch.

 

My 6" F20 Tinsley Cass explodes Jupiter & Saturn at 70x per inch, and its 2" CO has minimal affect on contrast.


Edited by Bomber Bob, 24 April 2019 - 10:44 PM.

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#70 memento

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Posted 25 April 2019 - 04:49 AM

Is your 5" SCT sharp at 70x / 80x per inch?  The Bresser AR-102L is.  My 1970s orange C5 Astro cruises at 300x, but the 1980s white-tube spotter topped-out at 50x per inch.

 

My 6" F20 Tinsley Cass explodes Jupiter & Saturn at 70x per inch, and its 2" CO has minimal affect on contrast.

I don't go much past 30–40x / inch because I find observing at those small exit pupils very disappointing. Staying at .7mm exit pupil, I can keep e.g. mouches volantes still under control. That's why I decided a 6" scope will take me further when watching the Moon or planets than any 4".

 

6" at 40x / inch equals 240x with a .64mm exit pupil. I think that's plenty under most "normal" seeing conditions. In those ultimate nights, you could go well beyond, but normally not. Actually I will be happy at around 180x most of the time, with this 6" that would mean a 10mm eyepiece and .84mm exit pupil. That would be a very relaxed viewing experience for me.

I certainly wouldn't mind a "non-compromise" Cass like your Tinsley, but try find one this side of the pond ...

 

Also would not mind an 8" scope, but then require a bigger mount and also will have more cooling issues. Last not least, the price of this new 6" CC is really tempting ...


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#71 Bomber Bob

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Posted 25 April 2019 - 05:49 AM

Yeah, my Tinsley's FL is 3000mm, and 240x with my UO HD 12.5mm Ortho is comfortable most nights -- especially after Majestic re-coated the mirrors.


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#72 Thandal

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Posted 25 April 2019 - 10:55 PM

... Last not least, the price of this new 6" CC is really tempting ...

Exactly!  lol.gif

 

While I appreciate all the observations about how the "Pros" for the CC6" I've selected can be equaled (or surpassed) on other scopes, I keep coming back to, "Not at that price."

 

BTW: Was notified today that mine has shipped from Orion and should arrive mid-week.

Will post a first-light report as soon thereafter as the weather cooperates. wink.gif


Edited by Thandal, 25 April 2019 - 10:56 PM.

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#73 Vondragonnoggin

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Posted 25 April 2019 - 11:13 PM

Exactly!  lol.gif

 

While I appreciate all the observations about how the "Pros" for the CC6" I've selected can be equaled (or surpassed) on other scopes, I keep coming back to, "Not at that price."

 

BTW: Was notified today that mine has shipped from Orion and should arrive mid-week.

Will post a first-light report as soon thereafter as the weather cooperates. wink.gif

I looked on Astronomics and the Astro-Tech CC6 is only $499. That’s considerably less than the $850 I paid for my iOptron new.

 

Not a bad deal for all that it is.

 

I’ll be interested to hear the report on how long it will hold collimation with local backyard use. I know the starblasts and 6” F/8 dobs hold collimation very well and infrequently need collimating. I’m just guessing that the CC6 will also hold collimation well.



#74 memento

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Posted 26 April 2019 - 09:51 AM

BTW: Was notified today that mine has shipped from Orion and should arrive mid-week.

Will post a first-light report as soon thereafter as the weather cooperates. wink.gif

Congrats to the purchase. Looking forward to any reports on this scope. waytogo.gif 



#75 Stephen Kennedy

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Posted 26 April 2019 - 02:23 PM

My RC6 arrived perfectly collimated from GSO six months ago and has stayed that way and would expect the CC to do the same.  Both the RC and CC made by GSO use fixed mirrors, unlike SCTs where focus is achieved by moving the mirrors, so once collimated they should stay that way for a long time.


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