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Sky Watcher 18" StarGate first review


raanany

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10 hours ago, Steve said:

Is this really your first telescope? If it is then you have jumped into the deep end. 

First things first, are you confident you have achieved collimation and allowed enough time for the mirror to cool to ambient temperature? 

I wonder what type of mirror is fitted to the telescope when sold in Israel. If you are able please post a photograph showing the rear of the mirror, we will then know if it is the early cast mirror or the more recent fused together mirror. 

Pretty much the first one, yes. I'm an "all or nothing" kind of guy. I had a toy telescope when I was a kid. A cheap 2" refractor with an internal (I found out when curiosity lead me to open it up...) 1" aperture limiter placed right next to the objective lens. As I said, a toy. But the dream stayed and I finally bought a real one. Sort of.

I'm confident I've achieved pretty good collimation using a laser collimator. I couldn't get the secondary mirror main screw opened (screw was jammed as I mentioned above) so only near perfect. I know that because when I fitted a 6mm eyepiece the diffraction rings around stars were centered almost perfectly. As for cooling down, I still didn't fit fans to the scope. Does it really make that much difference?

The mirror on my scope is the fused one with the ribs. Instead of taking a photo, I'm attaching one from an earlier post. Sorry about that...

post-54-0-29871800-1446158340.thumb.jpg.

 

Note that mine doesn't look that clean and shiny. I've got some manufacturing residues between the ribs. A hazardous looking blue coloured powder.

As for the eyepiece I used to try and watch M31 - it's the 31mm Nagler coupled with a Televue paracorr so I should be getting around 1 Deg FOV. I know that's not enough to see the whole object but thought the total 1.8Deg would mainly add light in frequencies I'm unable to see anyway.

 

Thanks for all the feedback guys. I'll post more when I gain more mileage.

Raanan

 

 

 

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Raanan

must say, I like your style, 18", 31mm Nagler, paracorr. No point hanging around, just get in there!! Look, once over the niggles, you'll get it moving around nicely and then you're in for a treat. Don't know where you are as I'm on the phone here, but if you've darkish skies, you're gonna be spoilt. I started at 6", then 10", then 16" and the wows got bigger and bigger. After looking through your big fella, looking through my 10" would probably disappoint you. Good luck on your adventure!

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I have a couple of larger Dobs and can confirm that large objects like M31 can be disappointing initially due to the small field of view even with exotic eyepieces, the dust lanes require moving the image off centre to see them at their best. Smaller spiral galaxies might be rewarding. Regarding the secondary mirror issue, the three adjusting screws impart considerable pressure on the central screw, you really need to back these off a fraction before trying to unscrew it.

I'm sure it will all come together in due course and that you have a lot to look forward to.

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1 hour ago, raanany said:

Note that mine doesn't look that clean and shiny. I've got some manufacturing residues between the ribs. A hazardous looking blue coloured powder.

 

 

Like this?

 

Cooling down a big mirror with fans can make a HUGE difference at high magnifications.

Didn't the scope include a light shroud?

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That mirror style is a real innovation, and should make for lighter larger cheaper mirrors in the future, if it works as a design.

When you watch a mirror go through varying shapes as they cool down, via the views through the eyepiece, you start to get an idea of the major impact on views that only tiny changes in temperature can have. With so many additional variables added to the rear of the Skywatcher  mirror, I would be amazed if the views would ever be comparable with a traditionally made mirror under the same conditions. I would be delighted to be proved wrong :)

That isn't to say you cant enjoy amazing views. My 18" dob has a slight astigmatism issue, but the views of galaxies under dark skies are still breathtaking.

Please keep us updated about your progress. I think Peter probably has a point about slackening of the 3 collimation screws first btw, but you live and learn :)

Tim

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2 hours ago, raanany said:

I'm confident I've achieved pretty good collimation using a laser collimator. I couldn't get the secondary mirror main screw opened (screw was jammed as I mentioned above) so only near perfect. I know that because when I fitted a 6mm eyepiece the diffraction rings around stars were centered almost perfectly. As for cooling down, I still didn't fit fans to the scope. Does it really make that much difference?

The mirror on my scope is the fused one with the ribs. 

If you have the fused mirror then it is bang up-to-date, which is good :smiley: 

To achieve good views you will need good collimation (you need more than the laser, ask your supplier for a Cheshire) and an understanding of your mirror's cooling requirements, and your sky's seeing conditions. 

I fancy a large-aperture Dobsonian myself so will be watching your progress with interest. 

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1 hour ago, Thonolan said:

Like this?

 

Cooling down a big mirror with fans can make a HUGE difference at high magnifications.

Didn't the scope include a light shroud?

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

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1 hour ago, Peter Drew said:

Regarding the secondary mirror issue, the three adjusting screws impart considerable pressure on the central screw, you really need to back these off a fraction before trying to unscrew it.

I'm sure it will all come together in due course and that you have a lot to look forward to.

 

1 hour ago, Tim said:

Please keep us updated about your progress. I think Peter probably has a point about slackening of the 3 collimation screws first btw, but you live and learn :)

Tim

Yes, I think so too :smiley:

Raanan, it is going to be fun watching your progress. Please keep us updated. 

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1 hour ago, raanany said:

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?

We are assuming you assembled the telescope indoors then took it outside to use. The mirror, having been indoors, will be warmer than the air outside. When you take it outside it starts radiating the heat (stored in the glass) into the atmosphere until its temperature is about equal to the outside temperature. If you try observing while the mirror is radiating heat it will be like looking through water. Here in the UK, we generally allow 10 mins cooling time per inch of aperture but this is approximate. If you can store the telescope in a shed or garage so its mirror is always close to the outside temperature you can be observing much sooner. 

Regarding fans, opinion is divided but most believe a fan shortens the necessary cool-down time. 

HTH

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8 hours ago, Steve said:

 

Yes, I think so too :smiley:

Raanan, it is going to be fun watching your progress. Please keep us updated. 

I relaxed the three colimating screws of course. The center screw wasn't the only one BTW. All screws show signs of prone-to-get-stuck. The main screws that hold the side rail bearings were all squeaking and weren't smooth to get in and out right from the start which is why I keep them in a jar with a bit of oil. They feel like they would rust quite fast if I won't  

 

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  • 3 weeks later...

I have to say I'm quite appalled by the choice of materials used in this premium telescope. What happened to stainless steel screws & covers designed to adequately protect an investment of £3500.00. I would have an easy decision to make- which carrier would it be returned on today or definitely by tomorrow. This is really taking the <Insert profanity of choice> & my money would be going to a manufacturer who deserved it. 

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So sorry to hear the problems you have had, the cover just highlights it all, corners cut. It is so sad as mine was only a little more expensive and is clearly in a different league to what you describe. Hope you can fix the issues and make it better.

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Vaseline on the bearings? Seriously?

It's really not that difficult to make a scope that works well if you apply a bit of thought. If you are set up to create this sort of thing then it should be even easier to make it with bells and whistles that all work as you (presumably) have the machinery. I have made things in my back garden with hand held routers and saws. It's just takes longer. Compare what you have with this. OK it's a different scale but they really are simple things in essence and it's annoying when companies cut corners. Stainless screws add almost nothing in the scheme of things.

 

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On 07/03/2016 at 16:06, Moonshane said:

Vaseline on the bearings? Seriously?

It's really not that difficult to make a scope that works well if you apply a bit of thought. If you are set up to create this sort of thing then it should be even easier to make it with bells and whistles that all work as you (presumably) have the machinery. I have made things in my back garden with hand held routers and saws. It's just takes longer. Compare what you have with this. OK it's a different scale but they really are simple things in essence and it's annoying when companies cut corners. Stainless screws add almost nothing in the scheme of things.

 

I would be furious to spend that much money on a scope and for it to come with such fundamental flaws.

However this is all too common nowadays.

Brand new landrover discovery and rangerover still fit aluminium bodies to steel subframe units and use plain steel fixing bolts and screws. You would think after 60 years of suffering electrolytic corrosion they would have learnt something. But no. Poor quality fixings, no sacrificial electrolytes, no rubber buffers, no galv coatings... 4 year old discos are needing the angle grinder taking to them to remove body parts when fixing accident damage. Sad state of affairs on a £60k + luxury motor.

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If the bearings had been teflon on pebbly Formica, no lubrication should have been needed at all.  In fact, the motion can be too smooth with too little sticktion to hold heavier eyepieces.

Reminds me of the Stabilite mirrors that Zambuto abandoned over a decade ago because it was too expensive to deal with print-through issues during figuring.  Has Sky Watcher found a way to deal with this?  Both were/are radial rib designs.

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  • 2 months later...

I agree with the review. I bought the 450p and it's not worth the money, the mirror cover is a joke and the backing also peeled off mine, luckily I had read about and glued it on properly, I haven't had any problems with it again. 

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I always feel it's sad to think that the cheap Chinese import might put a guy like David Lukehurst into difficulty but it seems it's very much the other way round.

Great review, very honest. For all its faults, and even though I'd go for a Lukehurst myself, I expect you'll get some great nights out with this when you've sorted it out. The dust lanes in M31 are, as Peter said, off centre and are very distinctive from a dark site and with the galaxy near the zenith. The elevation makes a big difference.

Olly

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The likes of Synta make workable kit available to the masses. The majority us who just need something that works well at a reasonable price to pursue a hobby are happy to spend a few hundred quid. I think though if I intended to start spending thousands I'd  be looking at someone a bit more specialised than Skywatcher.

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22 minutes ago, mert said:

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

As if by magic... :biggrin:

I am online tonight updating ZWO prices after the promo ended so noticed your email arrive. 

My colleague Martin will find and respond to your message when we open in the morning, please let him know the problem so we can arrange a solution. 

HTH, 

Steve 

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On 29 May 2016 at 17:40, ollypenrice said:

I always feel it's sad to think that the cheap Chinese import might put a guy like David Lukehurst into difficulty but it seems it's very much the other way round.

 

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

 

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