About eight months ago I took the plunge and purchased one of these new Dobson mounted reflectors with the optional GoTo mount. There does not appear to have been a great deal of discussion about them here on IIS, so I thought I would give a brief review of my experiences so far.
Firstly a summary of the items I consider to be less than satisfactory upon initial use/assembly of the scope:
Installed the finder scope & bracket into the mounting foot, and finger tightened the retaining screw. A few minutes it fell out of its own accord straight onto the eyepiece end, bending the housing. Installed again the same way, but found I needed to overtighten the screw with a multiwrench in order to hold the scope & bracket assembly securely. A right angle finder would be much better I have since installed a Celestron RACI unit a lot easier on the neck to use!
The Primary Mirror Assembly three adjuster locking knobs were of very poor quality I replaced these straightway. Also the threads for these in the base were not properly formed I tapped these out with a thread tap. The three adjuster screws/knobs could also probably be improved.
The wrap around light shroud had areas of faulty stitching I had these re-stitched.
Poor quality eyepieces supplied with scope.
There are not enough counterweights supplied even when operational with only all the supplied equipment an extra 3kg was needed to even come close to a balance.
Poor design of the counterweight attachment system the single long bolt threaded straight into a thin cast area of the PMA base is probably not up to the job, especially if additional equipment/weight is fitted to the top end. I will be re-designing this setup in the future.
Many of the fasteners are already showing signs of corrosion I will be replacing these with stainless steel ones where possible.
Poorly translated instruction manual, with poor quality assembly diagrams some actual photos would be much better, especially the ones showing fitting of the drive cable assembly. The instructions for fitting the light shield need to be included in the manual in their proper sequence. With the present separate instruction sheet I went to fit it as the last job, only to find I had to go back and disassemble some parts in order to fit it.
The shield itself is of poor quality plastic one day the telescope spent in the July winter sun and it deformed beyond repair.
It was good to see a cover for the secondary mirror included, but there is no way to secure it when the telescope is in a vertical position fitting of a Velcro retaining strap has cured this.
The primary mirror cover will not fit around the telescope struts when assembled trimming of the cover edge at the struts area was required. However, kudos to Skywatcher for this cover it is a much better quality cover than the flimsy plastic one supplied with my 16 Lightbridge.
Inside the cover is a foam pad adhered to the cover. Upon unpacking the unit the foam was found to have detached and lying on the mirror surface a better quality adhesive required.
And now the good stuff!
Very well packaged upon initial opening of the four boxes everything was found to be in pristine condition. For those who want to keep the scope as a transportable setup, enclosing the existing packaging in built to purpose plywood boxes or similar would provide excellent storage for long term use.
Using my Parkes GS 30mm eyepiece the star images are nice crisp points, with minimal coma around the edge, especially considering the F-ratio of the scope. A coma corrector may help here.
We tried a number of different good quality eyepieces with the scope, and kept coming back to the Parkes.
The GoTo system seems to work OK, and tracks quite OK for visual work at least I could centre an object, leave it for 10 minutes and return to find it still well in the FOV. The Synscan hand controller & software is reasonably easy to operate regular use and I expect to learn its procedures quite easily.
Spectacular views of deep sky objects including the Tarantula Nebula & associated LMC objects, M42 and The Trapezium, the Jewelbox open cluster, Eta Carinae & The Homonculus, as well as other Milky Way objects in this area. Sirius B was clearly resolved.
After a hot day here on Saturday the mirror design seemed to cool down quite effectively, by 8.00pm and true night we did not notice any problems that could be attributed to this. There appears to be provision on the PMA to fit some cooling fans (not included with the scope) if required in the future.
Please note I have only spent about 3 hours actually using the scope visually, so I am unable to give a fully detailed report of its capabilities at this time. However overall I am happy with it, as I believe this scope gives good value for money. A little time & $$ correcting its weak points as outlined above would be well spent. I fully agree with Skywatchers advice it definitely requires two people to setup / pull down, one person would never do it. Sometime in the future I hope to install it in a permanent setup, its sheer size & bulk stretches the boundaries of portability I think!
I trust you survived the hail the other day. Great review, I guess we were all expecting some quality issues from the mount - my EQ8 demonstrates that Skywatcher has still a way to go to make telescopes rugged enough for Qld!!!
Of course it's the optics that count and it sounds like yours are sweet. I look forward to hearing more about them as you get the sky time [for those who don't know Graeme, he's a VERY experienced visual observer].
I'll have to bring my 20" up for a side by side one weekend.
Regarding the finder, this is true even on the refractors like the Esprits. I immediately noticed what sadly you found out through it falling out. I cured this issue by epoxying on a strip of brass to the side of the finder stalk dovetail so that the too-short screw would make adequate contact and still leave room for tightening. This is a really shoddy part by SW. The gap between the dovetail foot and the shoe was easily close to 3mm on my sample, and the brass shim I used was 2mm thick. Conversely, an original Vixen has a 0.5mm gap, meaning only minor finger pressure holds it in.
It's what started the "put off" in my mind towards the Esprit refractors. Optically great, mechanicals and build quality NOT so (the paint on mine was terrible, as was the general fit and finish). But, thankfully, as I mentioned, great optics.
Thanks Graeme, as you say, there is a dearth of decent reviews about this particular scope, so it's good to hear some local first hand experience.
Gee those quality issues are a shame. I know for a 20" dob it's still possibly considered a "low end" scope (compared to Obsession, SDM, etc), but really some of those things are cheap to fix and should have been well and truly knocked on the head during the development stage.
I'm glad your limited time at the eyepiece has at least seemed rewarding - if an experienced observer says the views are good, then perhaps this mitigates some of the quality issues. Perhaps. Interesting to see it's a two-man job: there's a YouTube video of it being put together by one chap (Adriano), but to be fair it didn't look like much fun doing it solo.
I have never understood why the travel limiting lip on the SW finder scope
dovetail is at the front end of the dovetail instead of at the back, which
would prevent the scope falling out when the main scope is pointed above the horizontal. Unfortunately the finderscope only fits into the dovetail in one direction, so you can't fix it by simply rotating the dovetail 180 degs.
raymo
I trust you survived the hail the other day. Great review, I guess we were all expecting some quality issues from the mount - my EQ8 demonstrates that Skywatcher has still a way to go to make telescopes rugged enough for Qld!!!
Of course it's the optics that count and it sounds like yours are sweet. I look forward to hearing more about them as you get the sky time [for those who don't know Graeme, he's a VERY experienced visual observer].
I'll have to bring my 20" up for a side by side one weekend.
Thanks Jonathon, yes no problems with the hail just around my neighbourhood.
I somehow think a side by side comparison with your beauty will blow the doors off the Skywatcher!! A couple of other AAQ members are also considering these scopes and are keen to check it out, so I will try to organise a test drive one Saturday night soon here at my place - you are more than welcome to join us. I will keep you updated if you are interested. I look forward to some assessments from other sets of eyes!
Regarding the finder, this is true even on the refractors like the Esprits. I immediately noticed what sadly you found out through it falling out. I cured this issue by epoxying on a strip of brass to the side of the finder stalk dovetail so that the too-short screw would make adequate contact and still leave room for tightening. This is a really shoddy part by SW. The gap between the dovetail foot and the shoe was easily close to 3mm on my sample, and the brass shim I used was 2mm thick. Conversely, an original Vixen has a 0.5mm gap, meaning only minor finger pressure holds it in.
It's what started the "put off" in my mind towards the Esprit refractors. Optically great, mechanicals and build quality NOT so (the paint on mine was terrible, as was the general fit and finish). But, thankfully, as I mentioned, great optics.
Lewis,
Your experience sounds similar to my issues. Having owned a number of Chinese made scopes over the years, I went into this purchase fully expecting a few QC SNAFU's that would require attention. As with my previous purchases I was prepared to outlay a reasonable amount of time and expense to bring the unit up to an acceptable standard for me. So long as the optics are adequate for my useI am happy with the truism you get what you pay for.
My area of interest is double stars so at the end of the day as long as the central area of the FOV is clear and crisp, a 20" scope for under $10K is still a lot of bang for your buck.
Thanks Graeme, as you say, there is a dearth of decent reviews about this particular scope, so it's good to hear some local first hand experience.
Gee those quality issues are a shame. I know for a 20" dob it's still possibly considered a "low end" scope (compared to Obsession, SDM, etc), but really some of those things are cheap to fix and should have been well and truly knocked on the head during the development stage.
I'm glad your limited time at the eyepiece has at least seemed rewarding - if an experienced observer says the views are good, then perhaps this mitigates some of the quality issues. Perhaps. Interesting to see it's a two-man job: there's a YouTube video of it being put together by one chap (Adriano), but to be fair it didn't look like much fun doing it solo.
Patrick,
Fully agree with you, I went into this purchase considering it as a "low end" scope. As I mentioned to Lewis, so far it seems adequate for what I want to use it for. Like most things in life I suppose it is a compromise of cost versus fit for purpose considerations.
My area of interest is double stars so at the end of the day as long as the central area of the FOV is clear and crisp, a 20" scope for under $10K is still a lot of bang for your buck.
Graeme,
I use my 18" F4.5 quite a lot for double stars - especially for faint ones. I make use of a 7" off axis mask which really is useful, I would be interested to know if you intend to use a mask.
I somehow think a side by side comparison with your beauty will blow the doors off the Skywatcher!! A couple of other AAQ members are also considering these scopes and are keen to check it out, so I will try to organise a test drive one Saturday night soon here at my place - you are more than welcome to join us. I will keep you updated if you are interested. I look forward to some assessments from other sets of eyes!
From an optical perspective, you may be pleasantly surprised. I've peered through some very fine Skywatcher 16" scopes and I would be shocked if they released anything less than a good-one in their flagship range
Thank you for this review as I was recently looking for some first hand objective reviews on the Stargates. The non-critical hardware issues are unfortunate, but it appears that SW are consistently getting the optics right across their product range.
What part of the setup needs two people? Can you see a self modification to remedy this?
Very nice considered review. If the optics are good, well supported and hold collimation then the rest is really just cosmetic and can be fixed. I do like the conical mirror which, presumably, will cool a lot faster than my 2 inch think Galaxy slab of glass. Can you see any way to attach a wheelbarrow handle type construction without compromising the structure of the mirror box and rocker assembly?
Most of the development emphasis with the 20" has obviously gone to the optics - which Sky-Watcher generally are doing really well with. Obviously at that price point for a half meter aperture telescope there are going to be shortcomings with the secondary considerations. Sky-Watcher are providing within the access of the dedicated amateurs wallet, an aperture of telescope which has traditionally only been within the professional domain. For 8-10k, to obtain an enormous half-meter aperture, I'd be willing to upgrade a few parts here and there! Other than a self made telescope, the only other mainstream brand that comes to mind which are making this sized telescope for the amateur are Obsession telescopes, but I think from memory they are more expensive.
Good luck with that fantastic aperture telescope and clear skies!
Yeah, from what I can see on the website, a 20" Obsession with goto functionality would set you back somewhere north of at least $14k USD, and a 20" SDM (which admittedly are works of art with all the bells and whistles) might be upwards of $20k AUD once you've added the cost of the mirrors in. Ahhh, it's nice to dream though!
Very nice considered review. If the optics are good, well supported and hold collimation then the rest is really just cosmetic and can be fixed. I do like the conical mirror which, presumably, will cool a lot faster than my 2 inch think Galaxy slab of glass. Can you see any way to attach a wheelbarrow handle type construction without compromising the structure of the mirror box and rocker assembly?
Russell,
thanks very much. At present I am considering building some sort of trolley to move the assembled scope around with. Biggest problem with that is I don't have much in the way of hard stand/concrete pads in my back yard to set it up on for overnight use. I must say I am starting to lean towards setting up a permanent observatory of some design to house it permanently.
I use my 18" F4.5 quite a lot for double stars - especially for faint ones. I make use of a 7" off axis mask which really is useful, I would be interested to know if you intend to use a mask.
John,
As yet I have not used a mask. I have been imaging/measuring doubles since around 2008, firstly with a 6" refractor and for the last few years with a 16" Lightbridge. I have considered at times using one on the 16" but am yet to try it. My understanding is to use one to increase the scopes FL will help split tighter pairs, but then I would assume you must lose fainter components of the pairs. At present i can easily image those components down as faint mag 15.5 which gives me plenty of targets to chose from!
So, we did it. The team went around last night to give this rare beast a thorough shake down along side my 20" f5 with exquisite craftsman figured optics.
Despite the appalling weather of late, the sky was beautifully clear and the seeing very good. Not perfect but certainly the nicest I've seen in a long time. From early evening, my SDM was resolving all six of the four stars of the trapezium even on low power views!
So to the Stargate. I was amazed by the mirror. It's not 'normal' by any means, but in fact a composite conical-ish affair with glued vanes between two disks of glass. The largest disk is of course the f4 optical surface and the smaller rear disk allowed the mirror to be attached to the mount and provided the surface against which the collimation screws would rest. I have to admit to thinking 'that's never going to work'.
In the pre-dark sky we star tested against some brighter stars and noticed something a little strange; the airy disk pattern had a noticeably pinched look to it and tool a slightly triangular form. Hmm. Checked the collimation screws, all seemed ok. When focussed the stars were tight but the effects of scintillation showed some asymmetric spikes. The optical error was actually very slight, and unlikely to be noticed at all to the less critical eye, but it was certainly there.
But then something interesting happened...
We continued to observe into the evening, enjoying wonderful views of the Great Orion Nebula showing plenty of colour and bags of lovely contrast befitting a light-bucket, and we started checking out the globulars and galaxies there to entertain us. And it became evident that the mirror was performing better and better as the night progressed. Each time we bothered to de-focus the scope and check the airy disk, it was rounder and rounder. By mid evening, the mirror had reached thermal equilibrium and the image was quite perfect, with text book airy pattern and absolutely pinpoint star images. The mirror was certainly so good in performance that it was difficult to distinguish the view from my SDM that has a mirror that would cost new about the same as the whole of the Stargate!!!!
So, we can certainly conclude that the optics are indeed excellent but just remember that they are only performing at 'very good' until the primary has properly equalised. There are pre-cast positions for three cooling fans in the base. I suggest filling them if you get one of these.
Mechanically, the scope more than met my expectations. The whole thing was solid, held collimation all night, and slewed and tracked perfectly well. One thing that surprised me was how well it works in manual mode. Slip the clutches and it's very smooth and perfect for just cruizin'
So all the features of a traditional dob at half the cost. Yes there are compromises and shortcuts, but you get a heck of a lot for your money.
Nice one Skywatcher, it's a keeper
BTW: It's f4, so there is a ton of coma. My Paracor fixed that perfectly and the stars were tight right across the fov. Factor it into the cost, you really need it!
Thanks Jonathon, nice review. Still a two-person job to set up you reckon?
I'm interested (and jealous) of your seeing conditions - we were at Watt's Bridge Airfield past Esk last night, and anything higher than 50x was like looking through a kiddies wading pool.
