gaseous
31-12-2022, 02:39 PM
After 4.5 years of ownership, I figured it was time to give a moderately unbiased appraisal of the 20” Skywatcher Stargate GOTO Dobsonian telescope. I started doing a pros and cons list, but they seemed to overlap in areas so I’ve just provided my general thoughts.
For a mass-produced scope, you could do a lot worse in terms of the build quality. The whole thing comes in so much cardboard and foam that they must only fit about 3 telescopes per shipping container. The base and mirror rockers are both extremely solid. The truss poles are also very robust and would certainly suffice to give an intruder a sound trouncing should the need ever arise. If I was to be critical, perhaps the metal coating could be a little more scratch resistant, but these are easily covered with some matt black Dulux metal paint from Bunnings, which seems to be an exact match. As with a lot of scopes, the nuts and bolts tend to show slight indications of rust once the coatings are removed, but unless you’re stripping the scope down to individual parts every time you use it, this shouldn’t be an issue. If anything, the scope is perhaps a little too robust – fully assembled, it’s about 75kg, so it’s certainly not in the ultralight category and care has to be taken when lugging it in and out of wherever you store it, assuming you partially dismantle it during viewing sessions. If you kept it fully assembled on a dolly, rolling it out every night would be fine, but under Bortle 5 skies as I am, it’s not worth getting out at home, so it lives in pieces in its own trailer for the monthly (wishful thinking) dark sky trip. It certainly takes up a lot of room when disassembled.
Design-wise they could certainly make a few improvements. The supplied counterweights are very much undersized (3 x 1kg), and I require another 2 x 1.25kg gym weights to get things properly balanced to allow for a filter slider, coma corrector, and decent eyepiece at the other end. Over time the threaded hole which holds the weights via a long threaded rod has been stripped out, so I’ve had to McGyver my own counterweight fixing which works a lot better. They also provide a large black plastic screen/light shield for the opposite side of the focuser, which may be useful if you observe with a lot of nearby lighting, but I’ve never found the need to use it at a dark site.
The supplied light shroud works adequately enough, although 2m of Velcro is a pain to join neatly, and the ridiculous little ribbons to tighten up the ends are just plain annoying. The shroud itself is reasonably “loose”, not at all like some of those nice snug/tight shrouds you see on other scopes, and can tend to billow into the light path when it’s a bit windy. I (meaning my wife) ended up replacing the Velcro with a large black 2m zipper from eBay, which is much easier to install and avoids the need for the stupid ribbons.
The upper cage assembly with the focuser and finderscope is designed in such a way that you can’t rest it horizontally when disassembled, so I’ve needed to make a large timber box with foam inserts to allow it to rest safely. Like other Skywatcher scopes, the finderscope slides into its housing from the primary-mirror end of the works, so a loose finderscope will fall towards the primary mirror. Not such an issue with closed-tube Newtonians, but absolutely heart-stopping when it happens with an open truss design. The finderscope should really slot in from the open end of the assembly.
The truss tube ends are fixed with a bolt tightening mechanism with their own small built-in handle, which is very tedious to use. I removed these small “handles” and just use a socket wrench to tighten/untighten all these bolts. I can see why they’ve done it, but it’s a bit sub-optimal in my opinion.
That being said, the whole thing is pretty easy to assemble on your own providing you have a step-ladder and can lift a moderate amount of weight above head height (the upper cage) and lift a more considerable amount of weight (base and mirror cradle) off the ground.
A minor gripe, but the spider vanes are located such that you couldn’t install a filter slider (such as an Astrocrumb) inside the truss assembly if you wanted to.
Collimation is ideally a two-person job, as the complete disassembly between observing sessions puts things very much out of whack. Using a Hotech laser collimator, you really need to have someone looking down the guts of the scope to advise when the red dot is getting closer to returning up the drawtube – trial and error adjusting the knobs at the back of the primary then checking from the other end of the scope is a time-consuming exercise on your own.
A lot of general Skywatcher literature mentions the need to have a GOTO dob level and pointing north prior to beginning the alignment procedure. For some reason, the 20” Stargate is designed in such a way as to prevent the whole thing reaching horizontal. There is a small plate and bolt in the cradle assembly which prevent this, and while removing the bolt allows it to get closer to the horizontal, it’s still not perfect. Having said that, it normally doesn’t make a massive difference to the alignment, and once aligned, the GOTO accuracy is great and objects in the eyepiece remain accurately centred for over an hour. The GOTO/tracking functionality is pretty impressive – I normally align it at the start of the night and have trouble-free slewing/tracking from the on. The tracking itself is smooth and silent, whereas the slewing really gets the innards of the thing working to full capacity. Like most dobs, objects near zenith can be hard to locate.
Having said all that, the views are quite spectacular on all the brighter/larger objects in the sky. It is able to tease out detail on dimmer DSOs that a smaller aperture would not, or even make visible very dim objects which would normally be invisible. I have only looked through a “premium” large mirror once at Astrofest, so I’m in no position to make quality comparisons between the Skywatcher mirror and some of these mirrors which cost $10k-$20k on their own. I dare say that a side-by-side test would reveal some discrepancies in the quality of the views, but as the weakest link in that shootout would undoubtedly be my own eyes, I’m happy to accept that the mirror may or may not be up to the same standard as the ones that cost twice as much as my whole telescope. I’ve never pushed the magnification much above 400x-500x, but that’s been due to the seeing conditions, not the mirror itself. Certainly, the general consensus from people who look through it is that the views are very good indeed.
Overall, I’m very pleased with this telescope, given its “mass market” billing. Sure, it has some arguable design issues, and is a fairly substantial chunk of metal and glass to lug about, but once you set it up, it runs very well and produces some really breathtaking views. If Australia had viable cost-effective access to some of the larger ultra-light / ultra-compact dobs from overseas like Obsession and Hubble for comparison, this review may be revised somewhat. In the meantime, the Stargate 20" seems to be pulling its weight effectively enough, certainly at the excellent price I got it for in mid-2018.
For a mass-produced scope, you could do a lot worse in terms of the build quality. The whole thing comes in so much cardboard and foam that they must only fit about 3 telescopes per shipping container. The base and mirror rockers are both extremely solid. The truss poles are also very robust and would certainly suffice to give an intruder a sound trouncing should the need ever arise. If I was to be critical, perhaps the metal coating could be a little more scratch resistant, but these are easily covered with some matt black Dulux metal paint from Bunnings, which seems to be an exact match. As with a lot of scopes, the nuts and bolts tend to show slight indications of rust once the coatings are removed, but unless you’re stripping the scope down to individual parts every time you use it, this shouldn’t be an issue. If anything, the scope is perhaps a little too robust – fully assembled, it’s about 75kg, so it’s certainly not in the ultralight category and care has to be taken when lugging it in and out of wherever you store it, assuming you partially dismantle it during viewing sessions. If you kept it fully assembled on a dolly, rolling it out every night would be fine, but under Bortle 5 skies as I am, it’s not worth getting out at home, so it lives in pieces in its own trailer for the monthly (wishful thinking) dark sky trip. It certainly takes up a lot of room when disassembled.
Design-wise they could certainly make a few improvements. The supplied counterweights are very much undersized (3 x 1kg), and I require another 2 x 1.25kg gym weights to get things properly balanced to allow for a filter slider, coma corrector, and decent eyepiece at the other end. Over time the threaded hole which holds the weights via a long threaded rod has been stripped out, so I’ve had to McGyver my own counterweight fixing which works a lot better. They also provide a large black plastic screen/light shield for the opposite side of the focuser, which may be useful if you observe with a lot of nearby lighting, but I’ve never found the need to use it at a dark site.
The supplied light shroud works adequately enough, although 2m of Velcro is a pain to join neatly, and the ridiculous little ribbons to tighten up the ends are just plain annoying. The shroud itself is reasonably “loose”, not at all like some of those nice snug/tight shrouds you see on other scopes, and can tend to billow into the light path when it’s a bit windy. I (meaning my wife) ended up replacing the Velcro with a large black 2m zipper from eBay, which is much easier to install and avoids the need for the stupid ribbons.
The upper cage assembly with the focuser and finderscope is designed in such a way that you can’t rest it horizontally when disassembled, so I’ve needed to make a large timber box with foam inserts to allow it to rest safely. Like other Skywatcher scopes, the finderscope slides into its housing from the primary-mirror end of the works, so a loose finderscope will fall towards the primary mirror. Not such an issue with closed-tube Newtonians, but absolutely heart-stopping when it happens with an open truss design. The finderscope should really slot in from the open end of the assembly.
The truss tube ends are fixed with a bolt tightening mechanism with their own small built-in handle, which is very tedious to use. I removed these small “handles” and just use a socket wrench to tighten/untighten all these bolts. I can see why they’ve done it, but it’s a bit sub-optimal in my opinion.
That being said, the whole thing is pretty easy to assemble on your own providing you have a step-ladder and can lift a moderate amount of weight above head height (the upper cage) and lift a more considerable amount of weight (base and mirror cradle) off the ground.
A minor gripe, but the spider vanes are located such that you couldn’t install a filter slider (such as an Astrocrumb) inside the truss assembly if you wanted to.
Collimation is ideally a two-person job, as the complete disassembly between observing sessions puts things very much out of whack. Using a Hotech laser collimator, you really need to have someone looking down the guts of the scope to advise when the red dot is getting closer to returning up the drawtube – trial and error adjusting the knobs at the back of the primary then checking from the other end of the scope is a time-consuming exercise on your own.
A lot of general Skywatcher literature mentions the need to have a GOTO dob level and pointing north prior to beginning the alignment procedure. For some reason, the 20” Stargate is designed in such a way as to prevent the whole thing reaching horizontal. There is a small plate and bolt in the cradle assembly which prevent this, and while removing the bolt allows it to get closer to the horizontal, it’s still not perfect. Having said that, it normally doesn’t make a massive difference to the alignment, and once aligned, the GOTO accuracy is great and objects in the eyepiece remain accurately centred for over an hour. The GOTO/tracking functionality is pretty impressive – I normally align it at the start of the night and have trouble-free slewing/tracking from the on. The tracking itself is smooth and silent, whereas the slewing really gets the innards of the thing working to full capacity. Like most dobs, objects near zenith can be hard to locate.
Having said all that, the views are quite spectacular on all the brighter/larger objects in the sky. It is able to tease out detail on dimmer DSOs that a smaller aperture would not, or even make visible very dim objects which would normally be invisible. I have only looked through a “premium” large mirror once at Astrofest, so I’m in no position to make quality comparisons between the Skywatcher mirror and some of these mirrors which cost $10k-$20k on their own. I dare say that a side-by-side test would reveal some discrepancies in the quality of the views, but as the weakest link in that shootout would undoubtedly be my own eyes, I’m happy to accept that the mirror may or may not be up to the same standard as the ones that cost twice as much as my whole telescope. I’ve never pushed the magnification much above 400x-500x, but that’s been due to the seeing conditions, not the mirror itself. Certainly, the general consensus from people who look through it is that the views are very good indeed.
Overall, I’m very pleased with this telescope, given its “mass market” billing. Sure, it has some arguable design issues, and is a fairly substantial chunk of metal and glass to lug about, but once you set it up, it runs very well and produces some really breathtaking views. If Australia had viable cost-effective access to some of the larger ultra-light / ultra-compact dobs from overseas like Obsession and Hubble for comparison, this review may be revised somewhat. In the meantime, the Stargate 20" seems to be pulling its weight effectively enough, certainly at the excellent price I got it for in mid-2018.