Which 12" Scope Stays? Which goes?

[Carbon Brush]

I am in the situation of having two scopes that are quite similar. Being large, one will go. But which?

Seeking thoughts and opinions from the community.

A GSO Revelation 12" on dob mount and a Skywatcher 300PDS with rings.
Both are in good order with similar age mirror coating and both have a dual speed focusser.

The GSO is older, but has been well looked after. It could be argued the recoated mirror is not 100% like new having minor marks. But nothing worthy of further mention.
I have not run them side by side to be able to definitively say scope A contrast/resolution/brightness is marginally better than scope B.
The 300PDS is only a couple of years old and all but unused.

I have a goto mount capable of carrying the 300PDS. I also have an old (last century) mount that I could, with a bit of effort, adapt to carry the PDS in no frills alt-az mode.

Mods to the GSO dob include a wheeled trolley and improved balance weight arrangement. Two different handle arrangements are in my head, but not yet in hardware.
The 300PDS is still as supplied from the shop.

Neither scope has benefitted yet from flocking, better black paint or similar measures. These are (in my book) standard improvements for shop bought reflectors.
The scope that stays will be improved this summer.

Looking forward to your comments,

David.

 

[Peter Drew]

Binoscope?     🙂

[Mr Spock]

GSO should have the better optics.

[Astrobits]

17 minutes ago, Peter Drew said:

Binoscope?     🙂

Funny. That was my first thought.🤩

[Andy ES]

Initial gut feeling on what to do is always right 🤞

[rl]

How do the secondary mirrors compare?

The 300PDS is optimized for photography. Is this ever going to be of interest? If so you will need a big equatorial mount, is the GOTO mount equatorial?.

Is the GOTO actually useful visually or do you prefer to star-hop?

If you are visual only I'd take the one with the smallest obstruction. And the simplest mount...

[Peter Drew]

I would keep the one with the best optics, most other aspects can usually be DIY upgrades.  🙂

[CraigT82]

Don’t underestimate the challenge of getting a 12” newt up onto a mount, unless its permanently mounted then doing it again and again gets very unappealing very quickly. 

53 minutes ago, Mr Spock said:

GSO should have the better optics.

Please explain why you think this? 

[Carbon Brush]

25 minutes ago, CraigT82 said:

Don’t underestimate the challenge of getting a 12” newt up onto a mount, unless its permanently mounted then doing it again and again gets very unappealing very quickly.

Fully agree. I have 20Kg of Intes MN78 on my alter D6 mount - it tends to stay in place.

[Carbon Brush]

43 minutes ago, Peter Drew said:

I would keep the one with the best optics, most other aspects can usually be DIY upgrades.

Yes I agree. Any dob blance and stickiness issues can be improved or resolved with a bit of thought and practical work.

[Mr Spock]

36 minutes ago, CraigT82 said:

Please explain why you think this? 

Experience, and the reputation GSO have recently for producing good optics. I've had two 10" Skywatchers, and though very good, they aren't even close to the 12" StellaLyra (GSO) I have now. Having used high quality optics before, I estimate this one (I can't answer for others) to be at least ¹/₁₀  PV.

[bosun21]

It’s also the general consensus that the Taiwanese scopes have superior optics when compared to the Synta scopes manufactured in China. To what degree is debatable, but I do know that the 8” Stella Lyra I used to own and my current 12” does have great optics.

[John]

Good to see that GSO have upped their game now 🙂

I've owned 2 older GSO made dobs (8 inch and 12 inch), 4 Skywatchers (3x 8's and a 10) and one Orion Optics 12 over the years. The GSO's were OK but their mirror coatings degraded quickly and their mirrors were 1/4 wave PV at best I reckon (and that was what GSO claimed back then). The Skywatchers performed better and the coatings seemed more robust.

But it is good when a major producer improves their products over time and maybe even as a result of user feedback on forums sometimes ?

 

[Astroscot2]

1 hour ago, John said:

Good to see that GSO have upped their game now 🙂

I've owned 2 older GSO made dobs (8 inch and 12 inch), 4 Skywatchers (3x 8's and a 10) and one Orion Optics 12 over the years. The GSO's were OK but their mirror coatings degraded quickly and their mirrors were 1/4 wave PV at best I reckon (and that was what GSO claimed back then). The Skywatchers performed better and the coatings seemed more robust.

But it is good when a major producer improves their products over time and maybe even as a result of user feedback on forums sometimes ?

 

john, you never made comment on the OO you owned?

[SamAndrew]

6 hours ago, John said:

Good to see that GSO have upped their game now 🙂

I've owned 2 older GSO made dobs (8 inch and 12 inch), 4 Skywatchers (3x 8's and a 10) and one Orion Optics 12 over the years. The GSO's were OK but their mirror coatings degraded quickly and their mirrors were 1/4 wave PV at best I reckon (and that was what GSO claimed back then). The Skywatchers performed better and the coatings seemed more robust.

But it is good when a major producer improves their products over time and maybe even as a result of user feedback on forums sometimes ?

 

Agreed the GSO dob I owned was the only one I've seen with visibly degraded coatings, admittedly I don't know exactly how old it was as it was 2nd hand, but compared to my much older Tal-1, the GSO looked very tarnished.

[Zermelo]

My next scope purchase might be a 10" Dob, so I was interested in the discussion of GSO's tolerances.

The Stellalyra Dobs don't quote any, and I found quite a few other GSO ads that didn't specify.

But this one does quote "Diffraction Limited Optics (1/12 Wave RMS)", and the GSO mirrors sold here say "1/16 wave RMS at least, and often better" (I'm not sure how "better than 1/16 wave" helps, if 1/12 wave is already diffraction limited).
I'm also aware that unqualified statements like this are ambiguous at best.

Does anyone have any definitive info on GSO mirrors?
Do the same tolerances apply to all of their output, or do they vary?

[Carbon Brush]

@rl    A bit of a surprise here.

Both scopes are about 70mm on the minor axis!
This was done by holding a piece of card against the mirror and making a pencil mark. So is prone to error.
I think it fair to say the scopes have the same central obstruction.
The PDS has a mirror glued on to a stick. The GSO has the mirror in a carrier, with small clips.
The GSO has secondary collimation screws are on a larger circle, so should be easier to set up.

Looking at the scopes side by side, the tube construction means they are different lengths, with the focus in different locations.
Primary mirror depth in the tube differs between the scopes.
This indicates the PDS FL is lower than the GSO. Maybe by 50-100mm?
I haven't accurately measured to make sure the primary to secondary distances are correct in both scopes.
I suppose we tend to asume the scopes are assembled correctly and just collimate.
It is only when doing a side by side comparison that we think a bit more.

As for the PDS being optimised for photography, I think SW must mean it reaches focus fairly near the tube, rather than a long way in mid air.
Looking at the SW site, they don't list the 300 scopes. As for specifications generally. They are all but non existent.
This certainly does not tempt me to buy any of their products from new.

I am thinking in terms of the scope being visual. A light bucket.
Keeping this size scope steady for photography is a big effort.

Going back to the well used saying. The best scope is the one that gets used the most.

If it wasn't for the cloud and snow, I could take the dob outside, place it, and start looking.
Not exactly grab n go. Grab grunt heave and stagger. But on the trolley it is fairly easy.

For the PDS I would have to assemble a tripod and mount.
Or the pier and ancient alt-az mount I had in mind.
Then fasten the 24Kg of OTA, rings and dovetail.
If I was to remove the MN78 from my observatory pier, the PDS would be OK for permanent fitting.
But the MN78 views are something that I want to keep.

You can see that I am leaning very much towards keeping the dob. But not yet made a firm decision. I will sleep on it.

Thank you to all of you for your very useful and helpful comments. If there are other thoughts, do keep them coming in.
The community input has certainly made me look more closely and think about the options - and appreciate what a wonderful resource we have in SGL.

Thanks again, David.

 

[John]

8 hours ago, Astroscot2 said:

john, you never made comment on the OO you owned?

I don't want to take the thread off topic so I will just say that the OO 12 was a little better optically than the GSO or Skywatcher ones and, more crucially for me, weighed about the same as a 10 inch GSO / Skywatcher so was much easier to setup and move about than the GSO made 12 inch (which was a Meade Lightbridge).

Back on topic, it looks like @Carbon Brushis gradually and thoughtfully moving towards a decision now 🙂

Edited March 8, 2023 by John