Getting 4" F/11 ED frac OR 6" Classic Cass

[JP-Astro]

Hello gentlemen,

I've narrowed down my choice to one of the 2 telescopes and have hard time deciding between the two. They are both within my budget and I don't consider any other options. Only these two. Either one or another. None otherwise. (Would get them both but if I had money my choice of the scope would widen instead.)

- One is a (relatively) long focus 4" ED refractor (~FPL51 equivalent)  Starwave ASCENT 102ED F11

https://www.altairastro.com/starwave-ascent-102ed-f11-refractor-telescope-geared-focuser-467-p.asp

Another is a 6" GSO Classic Cassegrain (with a F12  focal ratio); A kind of reflector telescope that is.

https://agenaastro.com/gso-6in-f12-classical-cassegrian-reflector-ota-black.html

My primary interest are planets hence the focal ratio choice. 6" CC will give me more light gathering ability but I find something fascinating in refractors.

Please add any thoughts on the subject you might have. Of course think of it as if you were facing this dilemma.

[GazOC]

It's sounds like you're sold on the refractor and planets despite the pros and cons probably weighing in favour of the Cass being the more versatile scope overall?

If that's the case then go with the 'frac 👍

[Jforson]

I have the 102 f11 AA scope (non Ed) in red.  Lovely view at the eyepiece and good fun to use.   I primarily use for lunar and planets.  
 

However, as you will no doubt be aware it is a long scope and therefore needs a decent mount. I use the AA sabre mount with the following extension:

https://www.firstlightoptics.com/sky-watcher-mount-accessories/skywatcher-eq5heq5-extension-tube.html

Funnily I am actually thinking of adding a 6” SCT to the collection later this year. 
 

good luck with the choice. 
 

 

[Tenor Viol]

I have never used a real Cassegrain (just an SCT)... but the issue with the Cassegrain is likely to be that the obstruction reduces contrast and you don't get the benefit of all 6 inches. The advantage is it's more compact, which at f/11 and f/12 is a serious consideration

Edited July 5, 2020 by Tenor Viol

[mikeDnight]

I'm particularly fond of refractors but the classical Cassegrain is very interesting. Just to throw another spanner in the works I thought I'd add this scope into the mix, as this wouldn't suffer from spider diffraction, unlike the classical Cassegrain.

[fozzybear]

just one thought you do not state where you are based? one is sourced UK I'e Starwave and "out of stock" the other is state-side USA (import duty) + shipping 

[John]

Sounds like you would really like to go for the 102mm F/11 ED refractor

If that is the choice you make, do make sure that you have a mount that is up to holding the scope steady and without undue vibrations at high magifications. This will ensure that you can fully exploit what this type of refractor is capable of. The mount may need to be stronger than you think - the length of the tube, with this scope, will have much more influence than it's weight.

[JP-Astro]

Thanks to all of you for a bunch of thoughts so far. I'm in the Eastern Europe. German retailers have those scopes in different brands.

Yes, I know of the mount requirements for a long frac. My EQ5 would be at the edge of its stability. While 5" F11 gets good reviews I know that the GSO CC alternatively has a following within the CATs camp!

[AdeKing]

I also have the Altair 102 f/11 non-ed and it's a lovely scope but as has been mentioned above, it does need a decent mount and tripod.

My EQ5 mount copes with it when it is on a Berlebach Uni 18, but I wouldn't want to use it on a smaller mount as it's a long tube which is what the mount will struggle with rather than the weight.

The advantage of the ED version is that it's binoviewer friendly thanks to the removable section.

I've never used a classical casegrain, but am very happy with the 102 f/11.

Ade

[Chris]

According to the link the Altair is out of stock, so this might influence your decision depending on the lead time. There will be diffraction spikes on the planets with the classical cas, how do you feel about this?

[CraigT82]

The mak that mikedknight linked to, or the skywatcher 6" mak (skymax pro) would be my choice in this scenario. Sharp pinpoint views and much easier to manage than the long f11 frac. 

Edited July 6, 2020 by CraigT82

[dweller25]

I have compared a 102mm F/8 Triplet Apo, a Celestron C6 and the 6” CC.

Pros of the CC are :-

1. It is easier to use on my Vixen GP than the refractor due to it’s shorter length.

2. It cools down very quickly

3. Star shapes are excellent, very tight with a nice diffraction ring.

4. Contrast is unusually good for an obstructed telescope and certainly a match for the refractor.

5. ** It does not dew up ** 👍

6. Resolution is very slightly better in the CC over the refractor.
 

7. The scope is very well made and is fully collimatable.

Cons :-

1. It is relatively heavy - around 6.2kgs in normal use.
 

2. The focuser is poor - originally it  was not square to the secondary and needed adjusting and it tilts slightly with different weight eyepieces - whilst I have not done it yet I think it will be replaced.

3. Collimation needs to be VERY precise for best results.

I observed Venus with it earlier this year and was surprised at how sharp the image was, I could see shading across the planet surface which was a first for me.

Lunar views are excellent, good resolution and contrast - certainly as good as the much more expensive refractor.

I have yet to try it on the major planets but I am expecting it to be very good.....

Overall I think the 6” CC is a great scope and is excellent value for money but the focuser needs upgrading.

If it performs as well as I think it will on the major planets I will buy the 8” version.

Edited July 6, 2020 by dweller25