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GSO 8 inch classical cassegrain

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#1 Stopforths

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Posted 06 July 2020 - 06:28 PM

Taken the plunge on this scope in the guise of astronz.

claimed to be dielectric coatings.

 

Looks very nice out of the box.

 

I see a post where its alleged these scopes are only really 186mm!

 

My example has an f-3 primary 440mm approx between secondary and the primary  Secondary baffle is 68mm or 33.5 % obstruction.

 

The front baffle is 203mm.Everything appears right for a 203mm f12 Cassegrain with a 54mm secondary size needed.   

 

So this example won't be 186mm unless primary baffle vignettes.  Will startest when we get a clear night.

 

I sold a very good sw180 to buy this scope will be interesting to see if its as good or better on planets as the sw180.   

 

I expect faster cooldown.  Obstruction slightly bigger in the cass 33.5 v 30% but 2cm more aperture  20cm v 18cm. 

Attached Thumbnails

  • cc203.jpg

Edited by Stopforths, 06 July 2020 - 10:51 PM.

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#2 glend

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Posted 06 July 2020 - 08:15 PM

There are already threads on this scope, suggest you do some reading. I have one, no complaints. Don't nit-pick the specs, it is what it is, a classical Cassegrain, well engineered in my opinion, and a much better scope then the GSO RCs.


Edited by glend, 06 July 2020 - 08:18 PM.

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#3 Stopforths

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Posted 06 July 2020 - 08:42 PM

There are already threads on this scope, suggest you do some reading. I have one, no complaints. Don't nit-pick the specs, it is what it is, a classical Cassegrain, well engineered in my opinion, and a much better scope then the GSO RCs.

Done plenty of reading thanks. I'm not criticisng the design but will test to see if the suggestion its 186mm is true.  So far appears a full 203mm.

 

cheers

 

 

 

Phil Barker


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#4 Stopforths

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Posted 06 July 2020 - 08:46 PM

Who would love to see an f16 dall kirk version optimized for 1.25 inch fields?

 

With a f16 DK the secondary size would be 42.5mm versus 54 in the CC.     Means  around 26.5% with baffle.

 

Would have coma correction at edge of 1.25 inch field comparable to an f 7-8 Newtonian at edge of its 1.25 inch field.

 

food for thought a planetary killer in a compact design. 


Edited by Stopforths, 06 July 2020 - 08:55 PM.

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#5 jgraham

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Posted 06 July 2020 - 09:18 PM

I love mine! I have been using it for both imaging and visual, but I recently bought its 8" f/8 Ritchey-Chretien sibling, so the CC will likely end up being a visual scope. My initial impression is that it compares well with my Meade Mak 7. I found collimating the CC to be very easy and the fixed mirrors are very nice. I haven't touch the primary and I don't intend to unless absolutely necessary. I have a classic 6" f/20 Cassegrain that is a joy to use, but I had to collimate both the primary and secondary starting from scratch. One of these days I might even get it right. smile.gif

 

My baby...

 

Atlas GSO CC8 (5-26-2020)-2.jpg

 

 


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#6 chuckscap

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Posted 06 July 2020 - 09:30 PM

Classical Cassegrain is a very nice design.   From what I've read the "classic" proportions are an f4 primary with an overall f/16 giving a 25% central obstruction.   A DK with the same proportions would be very nice as well


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#7 Stopforths

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Posted 06 July 2020 - 10:52 PM

I love mine! I have been using it for both imaging and visual, but I recently bought its 8" f/8 Ritchey-Chretien sibling, so the CC will likely end up being a visual scope. My initial impression is that it compares well with my Meade Mak 7. I found collimating the CC to be very easy and the fixed mirrors are very nice. I haven't touch the primary and I don't intend to unless absolutely necessary. I have a classic 6" f/20 Cassegrain that is a joy to use, but I had to collimate both the primary and secondary starting from scratch. One of these days I might even get it right. smile.gif

 

My baby...

 

attachicon.gifAtlas GSO CC8 (5-26-2020)-2.jpg

have you tried a bino viewer is this possible?



#8 jgraham

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Posted 06 July 2020 - 11:33 PM

Not yet, but it shouldn't be a problem. I would just need to change out the spacing rings to give me enough back focus. Easy peasy.
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#9 Stopforths

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Posted 07 July 2020 - 11:25 AM

quick look last night wow 250mm plus back focus so binoviewing surely possible.   Seeing too bad to draw any conclusion other than cools faster than the sw180.



#10 Stopforths

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Posted 08 July 2020 - 11:19 AM

Collimation out a bit I found this morning in icy conditions.   Will try and tweak that.  No problems I'm sure I've collimated my 10 inch IM Mak Cass which involves primary and secondary adjustments.



#11 Stopforths

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Posted 09 July 2020 - 02:47 PM

Last night I dragged myself out of bed and having left the scope out after tweaking the collimation took to observing Jupiter and saturn.

 

Seeing pretty average but was able to use 200 x and the views came and went so to speak.  Jupiter was virtually overhead.  The southern alps are full of snow and this can affect the seeing.

 

Startest very  good virtually identical either side of focus and really snaps into focus.  Baffling very effective when Jupiter just out of the view I notice.  The Skywatcher 180 was similar on jupiter but the colour and purity of the image was better in the 8 inch Cassegrain.  More aperture probably.  Some really nice detail visible I felt like I was using a good Newtonian.  In really good seeing the SW was stunning in terms of fine detail hopefully the classical cassegrain is the same.

 

So clearly a performer got some little moments when the details on Jupiter really jumped out.   I noticed  an adjustment on the collimation ie unwind in all 3 screws evenly  brings focus forward.   I needed an extension where it is it must be close to 300mm behind the primary.

 

A dew shield will be needed.  Probably not a huge one I will work on that. 

 

While I was observing it reminded me of my excellent old Celestron c8 1994 vintage on jupiter.  That gave superb views and I owned it for around 6 years.   Lovely scope will try out on dso's etc and see how it goes.  Same for Saturn nice image very sharp plenty of detail at 200 X.

 

eyepieces I was using 12mm plossl 12.5 mm orthoscopic and 13mm Baader Hyperion.



#12 jgraham

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Posted 09 July 2020 - 07:09 PM

+1 on a dew shield, though there's not much room to mount one. After a long night of imaging I found that dew could make it all the way back to the mirror. I added a dew heater placed about 6" from the end of the tube.

Eventually I hope to compare the 8" CC with the Meade Mak 7.

Should be fun!
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#13 glend

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Posted 10 July 2020 - 03:29 PM

I have found that a dew shield is not required with the 8" CC, this is not a SCT or anything else with a front corrector. I live in the Southern Hemisphere, where it is mid winter,  right on the Pacific Ocean and have not had to use one. Humidity levels at night can exceed 80-90%, and tempertures well below dew point. My old MN190 Mak-Newt required corrector heater in these conditions, the CC does not. My one advantage maybe that it is located inside my roll off roof observatory, which is elevated above ground level, but some external tube condensation does happen after a couple of hours, but no secondary fogging, and certainly no primary fogging.

Now as to your 200x barrier, I can confirm that pushing high magnification is a problem, but not with the scope itself but with the Seeing conditions. You have a long focal length scope, and thus they are very susceptible to poor Seeing. 


Edited by glend, 10 July 2020 - 04:01 PM.


#14 Bill Barlow

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Posted 14 July 2020 - 11:42 AM

You can’t have temperatures below the dew point.  But they can be the same.  
 

Bill



#15 glend

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Posted 15 July 2020 - 04:17 PM

You can’t have temperatures below the dew point.  But they can be the same.  
 

Bill

Actually you can Bill. If you read my post I said, "...and temperatures well below dew point". This means dew could and does form below that temperature. In other words Dew was around, on the ground, but not on my CC mirrors which are inside my unheated observatory with the roof open.


Edited by glend, 15 July 2020 - 04:22 PM.


#16 Bill Barlow

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Posted 16 July 2020 - 09:35 AM

Actually you can Bill. If you read my post I said, "...and temperatures well below dew point". This means dew could and does form below that temperature. In other words Dew was around, on the ground, but not on my CC mirrors which are inside my unheated observatory with the roof open.

That doesn’t make sense.  As I said before you can’t have temperatures below the dew point.  Physically impossible.  Go look it up in the glossary of meteorology.  



#17 rutherfordt

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Posted 16 July 2020 - 11:12 AM

Actually, it is easy for objects (such as a telescope objective) to drop below the dewpoint through radiative cooling.  The sky is at about 100K at night which makes for quite a heat sink.  This also explains how frost forms on nights when the air temperature doesn't drop below the freezing point.  Same for dew-- objects can drop below the dew point even though the air isn't below it (or even at it).


Edited by rutherfordt, 16 July 2020 - 11:13 AM.

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#18 RichA

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Posted 16 July 2020 - 09:44 PM

+1 on a dew shield, though there's not much room to mount one. After a long night of imaging I found that dew could make it all the way back to the mirror. I added a dew heater placed about 6" from the end of the tube.

Eventually I hope to compare the 8" CC with the Meade Mak 7.

Should be fun!

That would be very interesting.



#19 Bill Barlow

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Posted 17 July 2020 - 09:32 AM

Actually, it is easy for objects (such as a telescope objective) to drop below the dewpoint through radiative cooling.  The sky is at about 100K at night which makes for quite a heat sink.  This also explains how frost forms on nights when the air temperature doesn't drop below the freezing point.  Same for dew-- objects can drop below the dew point even though the air isn't below it (or even at it).

Yes metal surfaces on a telescope can cool below the dew point but my point was the atmosphere will not cool below the dew point.



#20 Brian Carter

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Posted 17 July 2020 - 06:25 PM

That doesn’t make sense. As I said before you can’t have temperatures below the dew point. Physically impossible. Go look it up in the glossary of meteorology.

Dew point: the temperature at which water vapor condenses out of the air.

At a given temp, air can hold a certain amount of water vapor. If the temperature drops, water will condense out and form dew. This is how rain works: warm air picks up water, it rises high into the cooler atmosphere where is condensed into clouds and eventually rains.

Of course something can cool below the dew point, that’s why dew happens. And if surfaces did not cool below the dew point, they would never be covered in dew.

Edited by Brian Carter, 17 July 2020 - 06:27 PM.

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#21 Gray

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Posted 18 July 2020 - 02:49 AM

I used mine during 100% humidity for several hours and did have the secondary "fog" up.  The primary did not.  Used a hair dryer and after 10 minutes back to normal.  But, the entire outside of the scope was covered in dew.  Excellent telescope in my opinion and was like the OP said, a tad off in secondary collimation.  Star test showed same results, with excellent optics IMO.  Love this scope! 



#22 Stopforths

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Posted 18 July 2020 - 10:57 PM

Had another session on Jupiter and Saturn.  Nice crisp views on both.  I don't think its better than the good ole sw180 frankly very similar which is a good thing as that is a fine planetary scope.

 

Pretty happy with the star test will try and get some deep sky from a dark site over the next few days and report back.



#23 calypsob

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Posted 18 July 2020 - 11:53 PM

Can you use a reducer on these?



#24 Phil Cowell

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Posted 19 July 2020 - 05:54 PM

Your correct Bill, but the dew point can drop quite rapidly at times. Can cause fun with cooling rates of different materials the scope is made of.

 

That doesn’t make sense.  As I said before you can’t have temperatures below the dew point.  Physically impossible.  Go look it up in the glossary of meteorology.  


Edited by Phil Cowell, 19 July 2020 - 05:57 PM.


#25 jgraham

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Posted 20 July 2020 - 09:30 AM

I kinda like the idea of adding a dew shield if for no other reason than adding a bit more stray light rejection, particularly for imaging. As I mentioned above, I have had dew make it all the way back to the mirror. Since getting the RC version of this scope the CC will likely be used more for visual than imaging, so it probably won't be left out long enough for dew to be a problem.

As for a focal reducer... sure, if you can find one that fits. I'd consider picking up an 8" f/4 Newtonian with a coma corrector.

The right tool for the right job...


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