GSO 8" Classic Cassegrain Review

[glend]

The 8" Cassegrain arrived today, and it had some surprises in the box. First of all it is not the standard GSO white, but a high gloss black livery (as shown in the Orion video review), and the inclusion of both the substantial Losmandy lower bar on risers, and the top mount Vixen bar on risers, was welcome. Certainly this appears to be a step up in quality to the 8" RC which I had owned previously. I have attached some photos for you to perv.
Nothing else in the box, apart from the focuser extension tubes, but it was well packed on foam cradles, double boxed, bagged, etc. Just a comment on the focuser extension tubes (1x 50mm and 2x25mm) , they are substantial tubes with walls 7mm thick with ring baffling on the interior - again much more substantial than those thinner ones provided on my RC.

The scope tube itself is 53cm long - from back end of primary end to the front secondary ring section.
So off to the CGX it went and they seem well matched, as you can see in the photo. You will see in the photo from the top that these scopes now come with a Serial Number, which is nice to see. The tube is heavily baffled and the primary mirror is sparkling clean, not a trace of dust under bright light. Focuser looks like the standard RC one as expected, and the usual primary adjustment and lock screws are present - but I will never be touching those. Rumour has it that the CCs are well setup from the factory and collimation will be pretty close to perfect out of the box (if Larry Carlino can be believed). Any adjustment will be done at the secondary in a star test situation.
I need to work out which spacer rings I have to use for visual setup with my 2" diagonal and EPs, and hopefully that will happen tonight.


I will have more to say on the 8"CC after I do a star test and try it out tonight (hopefully). Very pleased with it so far.

[mental4astro]

Looks neat, Glen :)

I'm keen to hear your thoughts on the star testing!

Just a real shame that they painted the tube black. WHY???? :confused2:

Alex.

[glend]

High emissivity maybe, who knows? :shrug:

But I like it.

[Camelopardalis]

Nice one Glen :thumbsup:

Is the primary fixed? If so, it’s easy to collimate as an SCT, rather than those darn newts...

[glend]

Hey Dunk, well for the purposes of most people, yes it can be regarded as fixed. It is factory set. In Larry Carlino's review on Cloudy Nights, he found it to be spot on, but just did a small tweak to the secondary. I am hoping for something similar. Thankfully it did not have to bounce it's way across several states.

It does have adjustment screws for the primary, just like the RC models, but I will never touch them, they are factory set.
I will know more about the collimation when this darn cloud departs. There is a nice line up of planets from 3-4am in the morning, and I hope it clears by then.

[peter_4059]

I've never seen a dovetail bar with a serial number before. The OTA looks schmick.

[glend]

Well yes it is a strange place to put a serial number, as the dovetail can be removed, but at keast they are putting serial numbers on them now.

[glend]

I have had a good night finally, as the cloud disappeared as hoped. Went out at 2:30am to begin testing. The scope did not disappoint, and collimation was perfect, no tweaking required at all. Did star tests in various attitudes across the meridian and it was rock steady. Intra and Extra focus rings were perfect, and the sky was kind enough to allow good star test views. So glad that was good. Ran through a few doubles and saw very clear separations, despite the not perfect seeing. I have to mention Coma, I could not find any, if it was there it was not obvious visually in any field I looked at. Field size is not large, as you would imagine and this is a scope that benefits from a good mount properly aligned.
Moved onto the line of planets in the eastern sky, starting with Jupiter, Saturn and the Mars. Plus the bonus of Pluto lurking near Jupiter. Despite the proximity of the Moon flooding the scope i had very good non- Barlowed views, and detail was great, even pin point moons around the planets. Focus popped in fine. I was using a 2" 30mm Superview EP, then 20mm Superview, and 15mm Superview: equivalent of 81x, 121x, and 162x. I did try a 2x Televue Barlow but the sky conditions did not allow any improvement in detail. It was 17C with 74% humidity. In the hour and half I spent at the scope no fogging of the optics at all, it did certainly feel muggy with no breeze. A great first light result and I am very happy with this new scope.

PS, I must mention the detail the Moon revealed, it was amazing, the 30mm Superview just squeezing the whole sliver into its field of view.

[doug mc]

Collimation of this scope is dead easy. Mine was a little out. Center star, rack out to see out of focus rings with central secondary shadow, place a finger or pen in front of open tube, move finger shadow to thickest of rings. The closest collimation screw is the one to tighten. If you can collimate a SCT you can do these.

[doug mc]

Orion Telescopes has a manual for these scopes with collimation instructions.

[mental4astro]

Glen,

No disrespect intended for what you find appealing. Of course black looks good. Not a colour for scopes though. That's what I mean.

With planet season reaching its apex soon, a very good test of the optics will be if you are able to make out the Encke Division in Saturn's rings. Should be a cinch for a good 8" in steady seeing :thumbsup: Be able to see it and see it in good seeing (leaving excellent seeing aside) & then you really have a true keeper! These conditions will really put the Strehl rating of the optics to the test.

It's what separated the very good & excellent SCTs and Maks when I was testing them. All the scopes were able to resolve the Encke Division, but the slightly challenging conditions sorted out ultimate scope with how the different scopes were able to deal with the seeing. This is how the 7" Intes Mak won (pic below) from the other two very good C8's. I mention this to give you a usable guide by which to discern the quality of your CC's optics.

Alex.