Sky Watcher 18" StarGate first review

[ollypenrice]

19 minutes ago, Paul73 said:

 

Speaking personally. It brings the likes of Mr Luckhust's creations into reach. When you read comments such as "for only a little bit more ....." I get to thinking.... 

These scopes were mentally out of my league, but now I have a buch of proper observers telling me that it is worth the little bit extra!

Paul

 

It seems as if it's well worth the extra bit.

Olly

[gnomus]

Regarding Vaseline, I know very little about these things, but I though I read somewhere that you had to be careful about using such things because of the propensity to pick up grit and similar detritus and for it to turn into a sort of grinding paste.

[Obsession 30]

It's a shame when a manufacturer saves a few pounds and produces something that is poor quality and will lose them sales in the long run. Hope you manage to get things sorted and enjoy the scope

[neil phillips]

On ‎2‎/‎17‎/‎2016 at 12:12, raanany said:

Yes, exactly like this ugly blue stuff.

Question about the fans: If I wait long enough, the mirror's temperature should get to the surrounding air temperature even without fans, right? I mean, the fans can only blow ambient temperature air on the mirror. They don't have any active air-condition effect.

And another questions: Why do we consider the mirror to be hot to begin with? Is it the mirror's absolute temp that we care about or the delta to the ambient temp?

The scope included a shroud. I took the pictures before putting it on.

 

Raanan

My 300p needs two fans one at the front and back for quite some time 2 hours cooling from indoors to give reasonable results on planets. that Mirror design is different though looks thinner, but also larger

Edited June 11, 2016 by neil phillips

[niallk]

On 17/02/2016 at 12:12, raanany said:

Question about the fans: If I wait long enough, the mirror's temperature should get to the surrounding air temperature even without fans, right? I mean, the fans can only blow ambient temperature air on the mirror. They don't have any active air-condition effect.

Raanan

Re cooling with a fan - this link might be of interest. The layer of air in contact with the surface of the mirror which is absorbing heat is being swept away faster than natural convection with a fan, increasing the rate at which heat is lost to the air (I think!).

http://www.cruxis.com/scope/mirrorcooling.htm

Fwiw, I always use a fan on my 15" mirror if I'm viewing lunar/planets ... it is 2" thick! Your mirror is designed to inherently cool faster.

[Dave In Vermont]

The Vaseline would raise my eyebrows right off - and I'd remove it - all of it using solvents - and applying a PTFE (Teflon®)-based lube like SuperLube®. Then I'd try iy and see if it wasworth keeping the thing, or sending it back.

But that's me.

Best wishes -

Dave

[FLO]

On 1 June 2016 at 00:30, mert said:

I'll update when I hear back from FLO about sorting the issues I've had with my scope. 

A number of people are asking us about points raised in this thread so, rather than wait, here's an update from us. 

Mert has three concerns: His focuser sticks, his finderscope falls out of it's shoe and the Dobsonian base isn't as smooth as he'd like (this he says is subtle). 

The focuser is the same one fitted to every Skywatcher Dobsonian with an aperture 8" or over, it isn't unique to the Stargate-450p. We aren't sure why it is sticking (we'll know when we have collected it) but it will no doubt be an easy fix or replacement. The same is true of the finderscope, if you own any Skywatcher telescope with a 9x50 finder, it is the same. They don't normally fall out of their shoe but we are confident it too will be an easy fix or replacement. The base not running smooth was a mystery until Mert noticed it should be greased, but his is not. Somebody else had assembled it for him and hadn't applied the grease (perhaps the pot of grease normally supplied with the telescope was missing). I am guessing any good lithium grease will suffice but we have asked Skywatcher for confirmation. 

We are dangerously close to a happy ending  

We don't know about Raanany's Stargate-450p, it isn't one of ours (he lives in Israel). 

HTH, 

Steve 

[Louis D]

4 hours ago, FLO said:

Mert noticed it should be greased

I've owned several truss dobs, and not one uses grease on the side bearings.  Virgin Teflon blocks riding on Ebony Star Formica (or equivalent) should need no additional lubrication.  Nylon blocks can be substituted for Teflon to add a little more sticktion.

[FLO]

10 hours ago, Louis D said:

I've owned several truss dobs, and not one uses grease on the side bearings.  

This one does  

[FLO]

14 hours ago, FLO said:

I am guessing any good lithium grease will suffice but we have asked Skywatcher for confirmation. 

This is the grease Sky-Watcher recommend. 

 

[FLO]

Just found it at Amazon: 

Super Lube Synthetic Grease

[mert]

16 hours ago, FLO said:

A number of people are asking us about points raised in this thread so, rather than wait, here's an update from us  

Mert has three concerns: His focuser sticks, his finderscope falls out of it's shoe and the Dobsonian base isn't as smooth as he'd like (this he says is subtle). 

The focuser is the same one fitted to every Skywatcher Dobsonian with an aperture 8" or over, it isn't unique to the Stargate-450p. We aren't sure why it is sticking (we'll know when we have collected it) but it will no doubt be an easy fix or replacement. The same is true of the finderscope, if you own any Skywatcher telescope with a 9x50 finder, it is the same. They don't normally fall out of their shoe but we are confident it too will be an easy fix or replacement. The base not running smooth was a mystery until Mert noticed it should be greased, but his is not. Somebody else had assembled it for him and hadn't applied the grease (perhaps the pot of grease normally supplied with the telescope was missing). I am guessing any good lithium grease will suffice but we have asked Skywatcher for confirmation. 

We are dangerously close to a happy ending  

We don't know about Raanany's Stargate-450p, it isn't one of ours (he lives in Israel). 

HTH, 

Steve 

Nearly correct, My father assembled the scope and it looks like he thew out the grease in error  I have been away and not looked at the scope for a while.  

I ordered some new grease for him from Amazon. I heard this morning that a neighbour greased the runners and the scope is running smoothly. So the main issue has been resolved, it was a user error. 

Edited June 21, 2016 by mert

[mert]

When I'm next up visiting my dad I'll have a look and see if these other small problems are also user error

[FLO]

5 minutes ago, mert said:

When I'm next up visiting my dad I'll have a look and see if these other small problems are also user error

To be fair to your Dad, a Stargate-450p is a lot of telescope for a beginner  

I am sure he'll get the hang of it. 

Steve 

[mert]

16 minutes ago, FLO said:

To be fair to your Dad, a Stargate-450p is a lot of telescope for a beginner  

I am sure he'll get the hang of it. 

Steve 

To be fair I was thinking of myself when the purchase was made lol

[niallk]

Hope everything is coming together with the scope Mert.

Best of luck,

-Niall 

[mert]

Cheers Niall

I spoke with my dad last night, after applying a little grease the scope appears to be running smoothly. I haven't been up to visit for a while but urged him to look over the manual again, I sent  him a PDF copy also lol  

[Timebandit]

Hello. And thank you for doing that review. I think it will help a lot of people when deciding on a possible big scope. We all think about a larger aperture and how it would be nice to have our own big dob.

But your review has certainly picked up the size is not everything argument. And has highlighted even if you have a big budget scope of around £3500 mark that you may not get the scope of your dreams and in your case it seems to be reflected in your review that you are very disappointed.

I had a similar decision not so long ago as I wanted to start getting into the big dob dream. And had looked into this model as well 16". I am glad after all and especially after your review that I did not opt for this scope and instead decided to go for an Orion Optics uk. The main thing that swung this was the OO build quality is good , but it's the mirror that really swung it in knowing what Quality in pv you have got in your scope. Therefore in the end I did get a 14" 1/10pv and I am very happy with the build quality and pv mirror.

I do hope you get your problems with your Stargate sorted out, but this review does highlight that size is not everything. 

[Peter Drew]

I no longer use PTFE blocks to support the weight of Dobsonians over 16" aperture. It seems better to use stainless steel ballrace bearings and stainless steel strips on the side bearings and a stainless steel disc running on bearings for the azimuth axis. Damping of the bearings is applied by adjustable PTFE "brake pads" which allows the movement effort to be set as preferred.  

[Louis D]

4 hours ago, Peter Drew said:

It seems better to use stainless steel ballrace bearings and stainless steel strips on the side bearings and a stainless steel disc running on bearings for the azimuth axis.

I seem to recall seeing a goto truss design similar to this.  The bearings reduce friction to a manageable level for the slewing/tracking motors.  Still, there's no grease outside of the bearing races.

[raanany]

Been out with the scope lately and would like to share my updated findings with you guys.

First I'm happy to report that the optics of this scope are pretty good. There was an Obsession 20" f/5 at the same location (albeit a week earlier when I didn't have my scope with me) that I could compare with and I was surprised to see that the views in my 18" Skywatcher were nothing to be shy about.

Eyepieces: 31mm Nagler, 21mm Ethos, 10mm Ethos and 6mm ethos. All were coupled with Paracorr 2 and occasionally Orion's Ultrablock filter.

Venue: Negev desert in south of Israel (Borot Lots). Supposedly, the darkest place you can find in Israel, around 900m high. Except for some annoying humidity after midnight and some annoying wind at sunset, the sky was amazing even without the telescope. 

Objects:

M51 using 21mm and 10mm looked amazing! I didn't see more details with the 20" obsession so felt pleased with my scope.

Veil nebula: Beautiful details on both scopes. 52 cygni looks like in pearl sitting inside lace. Just beautiful. 20" showed more details but the comparison is a bit unfair because it was equipped with a Lumicon UHC and a Lumicon OIII (too much contrast for me) and I was using Orion's Ultrablock. Also, the Obsession was coupled with a different eyepiece. I think it was a Panoptic 24mm. When I get to put the two scopes one next to the other and swap filters and eyepieces, I'll report again. I got to see the veil also with a DGM NPB using my scope and it was better than the Orion Ultrablock.

Cat eye - Beautiful. Could see the star at the center clearly.

Ring Nebula - beautiful view. 

Jupiter/Mars/Saturn - This scope is not built for planets. With such high brightness you'd want to use high magnification. The problem is that without tracking and with such lousy alt bearings, you can't even manually track :-( My 6mm eyepiece was sitting useless. The view however, was as good as with the 20" Obsession so I'm guessing that in terms of Mirror quality, the 18" Skywatcher isn't bad even at high magnification. I'll update when I get to use it in better seeing conditions. I felt the limiting factor wasn't the optics.

 

Build quality / Usability

Sorry to keep moaning about this but the following [removed word] me off:

1. The shroud is not so well designed. The fabric has these ribs (strips) of flexible material embedded into it to keep it rigid and out of the optical path and these can (and will) twist inside the fabric and make it hard to fold around the scope. The scope's design also doesn't let you keep the shroud away from the optical path and it keeps getting in the way even when there's no wind.

2. The alt bearings suck. Even with ample lubrication there's just too much static friction. This is very annoying when you're trying to track an object at high magnification. You keep losing it until you give up. One has to apply too much force to overcome the static friction and once you've won the fight against it, dynamic friction kicks in and is by far weaker so you end up overshooting EVERY time. The Obsession on the other hand was smooth and fun to operate.

3. The mirror cover is... well... I don't want to get banned for profanity so I'll just shut up.

 

That's it for now. I'll update when I have some new findings.

[Beulah]

Thanks Raanany for your review. What a beautiful image. I have always wanted to stargaze in the Negev. I have heard from other Israeli members here how great the skies are there.

Sounds like the mirror is up to Synta's usual great standards; which is pretty good. Such a shame about the build quality. I was quite keen to own one; now I am not so sure.

If it were mine I would consider some serious retrofits, and even then, it might not be worth purchasing at that price point to have to make serious adjustments for optimum alt movement.

[Louis D]

Before giving up on the scope's altitude bearings, try locating a sheet of pebbly, gloss formica.  In the past, Wilsonart Ebony Star Formica was the go to choice, but I think it's discontinued, so you'll have to locate something similar.  Ask around on the ATM forums what's best these days.  Cut the sheet into strips and glue them to the curved bearing surfaces attached to the mirror box.  Next, locate some blocks of Teflon (PTFE) and countersink screw them to the rocker box, one toward the front and one toward the back of the bearing surface.  Check that Obsession's bearings, I think you'll find a setup similar to this to guide you.  Nylon can be substituted for Teflon if the motion has too little sticktion for your liking.

[FLO]

Mert's Stargate 450p is now setup at our premises in Exeter, if anyone would like to come take a look they will be welcome  

Steve 

[mert]

On 14 July 2016 at 16:04, FLO said:

Mert's Stargate 450p is now setup at our premises in Exeter, if anyone would like to come take a look they will be welcome  

Steve 

Thanks for all your help Steve. My father is delighted.