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Which scope altair f11ed vs 6"GSO CC

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#1 ScottW

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Posted 09 July 2020 - 09:37 AM

Hi,

 

I'll be posting this question twice, here and in the Cat forum, so I don't miss anyones input.

 

Which would be the better choice?  I'm not a beginner and know the strengths and weakness of both designs but have no experience with cats.  I would be purchascing either without that benifit. Mounting of either is not a problem nor are any related associated equipment.

 

I am a 100% visual observer and will stay that way.  My major areas of observations are double stars and the moon. I wish not to buy a headache, a scope that I must fiddle with.  I want as best star presentaion that a scope of this price range can have.

 

Thanks for any help,

 

Scott



#2 Hesiod

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Posted 09 July 2020 - 10:01 AM

As far as "star presentation" and "fiddling", the refractor has for sure the edge; and as long as can deal with its not trivial ergonomics, for the planned use a good 4" makes a lot of sense.

 

"CATs" (or "CASSes" as in the present case) can be very proficient too, but are more "complex" in their design and therefore, at a given price, more likely to have compromises than Newtonians (by the way, why not a Newtonian?) or refractors.

If a given optical quality can be assured to you, or have the possibility to toroughly test it, those extra 2" have for sure a weight; however have to live with spiked stars and be ready to adjust the optical elements sometimes (those CC may be "nasty" since both mirrors and the focusers could be adjusted, unlike SCTs and most MCTs where have just a single optical element adjustable, and for the rest are hit or miss).

The fairly large central obstruction may be under some circumstance even an advantage, but it is another factor to take into account.

 

Therefore I think that the refractor would be the safest bet: an f/11 doublet with ED glass has very good chances to be virtually perfect, while a 6" heavy obstructed Cassegrain really need bloody good mirrors to attain the same level of optical accuracy


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#3 Astrojensen

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Posted 09 July 2020 - 10:01 AM

 

I wish not to buy a headache, a scope that I must fiddle with.  I want as best star presentaion that a scope of this price range can have.

Then by all means stay away from the RC. You want a refractor, nothing else. 

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 09 July 2020 - 10:02 AM.

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#4 JKAstro

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Posted 09 July 2020 - 10:07 AM

Hi Scott. 

 

In my experience double star viewing is more pleasurable in a refractor than in a mirrored scope as stars are just a bit more pinpoint.  As far as lunar, I think it'd be a tie, with the slight edge in crispness the refractor gives being slightly offset by the higher horsepower and brightness of the larger scope.  As far as fiddle-free, a good refractor is about as fiddle-free as it gets.  The F11 ED scopes have gotten rave reviews on the forum here as well.  The refractor would be my vote.

 

JK


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#5 bobzeq25

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Posted 09 July 2020 - 10:35 AM

Then by all means stay away from the RC. You want a refractor, nothing else. 

 

 

Clear skies!
Thomas, Denmark

Agreed.  And this is not a close call, it's an easy decision.



#6 cst4

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Posted 09 July 2020 - 10:37 AM

I would go with the refractor, assuming that long F/11 tube isn't a problem to move around and mount for you.  The extra 2" of aperture on the GSO classical cass would help some with fainter DSO's but the refractor would definitely have the edge on double stars and the moon.  ED optics at a long F/11 would be extremely hard to beat when it comes to view quality. 


Edited by cst4, 09 July 2020 - 10:37 AM.


#7 ScottW

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Posted 09 July 2020 - 11:55 AM

Hi,

 

Thanks for the input.  It does seem that the refractor might be the one.  I'll just check how it will fit in an Explordome.

 

Once again, thanks.

 

Scott



#8 SteveGR

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Posted 09 July 2020 - 01:28 PM

The refractor will give a nicer contrast and clarity.  You'd get more light from the 6" but the diffraction effects IMHO would negate the benefit.  If it were a choice between the refractor and say, a 8" or larger, that might be a different discussion, but from the two listed, I would take the refractor.



#9 ris242

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Posted 09 July 2020 - 03:31 PM

Ignoring the scopes, with you're talking R&P focuser on the refractor and crayford on the GSO?

 

The GSO crayford I once had, was just plain awful and could slip without a lot of weight........new or adjusted.

 

The R&P on my TS f/11 has dealt with everything I've put on it, no trouble.



#10 Tropobob

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Posted 09 July 2020 - 04:36 PM

I would go with the refractor.   

 

Ha, Ha, I did. I received it this week.  

 

 

Attached Thumbnails

  • TS Scope 043A.jpg

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#11 Tropobob

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Posted 09 July 2020 - 04:38 PM

I have only been able to use this sparingly because of the weather.  What has surprised me is how much I enjoyed the views of globular clusters. 

Attached Thumbnails

  • TS Scope 049A.jpg

Edited by Tropobob, 09 July 2020 - 05:46 PM.

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#12 jgraham

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Posted 09 July 2020 - 06:16 PM

An interesting question, but an easy answer.

 

I own several Cats, Casses, and refractors, including an Orion 102ED and an 8" f/12 GSO Classical Cassegrain (I also have a 1970's vintage 6" f/20 classical Cassegrain). I also enjoy double star observing. The 8" CC was actually a pleasant surprise, it gives a nice sharp image with a surprisingly flat field in a very compact package. I'm curious to see how it ultimately compares with the Meade Mak 7.

 

However...

 

Overall, I have found that the performance of a refractor compares well with a Cat that is 2" larger, in part due to the light losses of the Cat's central obstruction and multiple reflections. In theory you gain a bit of resolution with the larger Cat, but in practice you give some of that back because of the diffraction caused by the central obstruction and in the case of the CC the spider for the secondary. There's also a bit of fiddle factor with the CC; in order to get the best performance you need to take the time to zero in the collimation and to keep it there; close is _not_ good enough. When the collimation is spot-on they can give wonderful images, but when it's off the damage to the symmetry of the diffractions rings can be irritating as well as the diffraction spikes from the spider. 

 

The unobstructed optics of the ED will give such a clean image and the performance of a 4" refractor will be very close to that of a 6" CC, I'd opt for the refractor.

 

Now the 8" CC would be a different matter, but you'd still have the collimation fiddle factor and the diffraction spikes.

 

Food for thought.



#13 daquad

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Posted 09 July 2020 - 06:37 PM

Double stars and the moon?   No headaches?  No fiddling?   No contest.  4" f/11 ED.  

 

Dom Q.



#14 Don Taylor

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Posted 09 July 2020 - 09:35 PM

I have the 102F11ED and it's a keeper. Mostly do lunar and planets (again soon) from the light polluted backyard - but I do go looking for the Brighter DSOs as well. Last May I took it to the club's dark sky site (which is not all that dark but way better than at home) and I could detect the nuclei of both M51 and companion with some hints of spiral structure.  M13 was partially resolved. Not my best tool for DSOs but In was surprised at what could be seen.

 

As a lunar scope its fantastic with superb contrast. Enough said.

 

Click on the photos and a larger view opens up.

 

850 5018 4362
Starwave 102 F11 ED assembled

Edited by Don Taylor, 09 July 2020 - 09:38 PM.



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