Sky-Watcher 20" Stargate 500P Dobsonian

[Rickster (Rick)]

Originally Posted by electric

Rick, great to read your experience is a good one.

If you are referring to my post, my experience was not with the goto model, but the push-to.

At SPSP, Skywatcher had a 20" goto. Obviously not your scope as it sat unattended and unused on the Saturday night, laid up with major mirror issues. I am surprised that this has not been brought up at all here. The Skywatcher flagship scope sits idle, much like the Australian Navy's flagship...

I sincerely hope your mirror is a good one No one drops this amount of money for anything but a good experience

Hi electric,

Yes, as I stated in my previous post, I haven't experienced the issues that you mention. With the clutches disengaged the operation is smooth in manual mode. Anything less and I would be asking for a refund!
As far as the mirror is concerned, I have only heard good reports but I'm yet to view so I cant comment as yet.

Cheers

[Rickster (Rick)]

Set up my rig for a brief viewing in a light polluted limited viewing window area last Friday night.
After collimation was complete I setup goto and pointed to some DSOs. I could only view some 6 to 7 magnitude targets but the view was amazing.
Next I pointed to Jupiter and Saturn but for some reason I couldn't get sharp images and also couldn't get my binoviewers to work. I need to look into this further. Not sure if the viewing conditions were bad but planets were disappointing. Next time I will setup my 14" dob also and compare. With the 14" I get great views of planets and binoviewers work a treat.
Surely a 20" mirror should give me more detail in planetary views? Any ideas?

Cheers

Rick

[gaseous (Patrick)]

I've heard binoviewers can be ornery critters depending on your available focusser travel. In a skywatcher dob you can adjust the poles to get the necessary in-travel, but not sure what you could do with the stargate if you're struggling to reach focus.

Viewing-wise, the seeing may have been a bit poor, resulting in sub-optimal planetary viewing, although when I bought my 16" dob I was told the planets wouldn't be as good as in my 8" dob. I didn't really delve too deeply into the whys and hows, but I'm sure there's a reason why this may be the case - maybe the larger aperture creates an image that's too bright?

[raymo]

The larger a scope's aperture, the more it is affected by poor seeing.
On nights of good seeing or better, your 20" will blow your 14" into the weeds,
but on fair to average nights you won't see much difference [on the
planets]. You could make up a matt black cardboard aperture stop, say 16" and
see if it helps on nights of poor seeing.
raymo

[Rickster (Rick)]

Thanks for the info,

I think the viewing conditions were poor but the DSOs were impressive. Cant wait for good seeing conditions!
I'll give the cardboard aperture stop a try if I cant get better results.

In regards to my binoviewers, I use a 2x Barlow and it works great with my f4.5 14" Dob. In fact I now mainly use the binoviewers with this telescope because they are the perfect for most of my observing.
It seemed with the 20" that I could get focus but the image was blurry, I need to setup again and try and work out what's going on. Unfortunately, weather is iffy in Adelaide at this time. I guess it is winter.....
There's a youtube vid where they setup binoviewers with the 20" Stargate. They're different type to mine but need to find out what they use to make it work.

Cheers

Rick

[AstroJunk (Jonathan)]

As Raymo says; Seeing.

I have a top draw 20" with a superb mirror that on a good night can split Sirius wide open and give planetary views like a Go/Peach image. On a bad night, I might as well be using a $30 scope from toys'r'us!!!

When that stunning night comes, you will know just how well that telescope can perform

[Rickster (Rick)]

Thanks all for the info, I didn't realise images would be worse on a bad viewing night with a larger mirror. I just expected them to be better than a smaller telescope on a bad night or any night.
Looking forward to some good viewing nights

Cheers

[sopticals (Stephen)]

Always find larger apertures give more detailed views regardless of seeing. Comparing 25" and 33" to 14" (and less), is like comparing 18 mega pixel visual images to 12 (and less) mega pixel ones.

Stephen.

[tonybarry (Tony)]

Fellow club member Ted Dobosz recently circulated this article about aperture and seeing:-

http://www.skyandtelescope.com/astro...ng-the-seeing/

It contains many gems of wisdom. A take-home message might be that aperture is always going to help, where it can. But it will not help where it can't ... if the seeing is bad, then it's bad for every telescope.

Regards,
Tony Barry
WSAAG

[Steffen]

Originally Posted by sopticals

Always find larger apertures give more detailed views regardless of seeing.

I cannot agree without a couple of important caveats.

A larger instrument will obviously show details that are too dim to be seen in a smaller one. A lot of detail in faint fuzzies can only be seen from certain apertures up. This is simply a matter of light gathering.

With bright objects (moon, planets, many double stars) on the other hand I find that smaller scopes outperform larger ones quite regularly. For example, my puny 6" Mak routinely throws up better views of the planets than our club 30". I believe that is because 6" scopes can be made with excellent optics while still being affordable for the average amateur. Large telescopes cannot. And no, I don't consider a $20k SDM an affordable telescope for an amateur.

This is why I believe amateurs with finite budgets need to find their own sweet spot on the aperture scale between the opposing slopes of optical quality and light gathering power.

[Rickster (Rick)]

The main reason I purchased the 20" was to view the faint fuzzies and obviously to get better views of the not so faint DSOs. I assumed I would also get more detail from planetary objects also but this is all interesting as there seems to be different takes on the subject.
I do remember going to Ian Bedfords Stockport SA observatory many years ago and seeing amazing views of Jupiter through his 30" Newtonian Cassergrain. I've never directly viewed such great views of Jupiter through a smaller telescope.

Rick

[geolindon (Lindon)]

Thanks for this thread.
Rick thanks for sharing your experiences, Patrick drew my attention to your post re 20 mins set up time. I am considering a non go to version and wonder what if any portion of that 20 mins is setting up the go to?
regards, L

[Rickster (Rick)]

Originally Posted by geolindon

Thanks for this thread.
Rick thanks for sharing your experiences, Patrick drew my attention to your post re 20 mins set up time. I am considering a non go to version and wonder what if any portion of that 20 mins is setting up the go to?
regards, L

Hi,

My advice would be to buy the goto version. I actually got mine for the price of a non goto unit including delivery to Adelaide from Skywatcher in NSW.

Just a few points to consider before you purchase this unit -

1. Setup is around 20 mins with mirror cradle on base and this includes setting up goto. Goto is quick and easy to setup once you are familiar with it.
2. I modified the Mirror cover (which is flimsy), so that it stays on while I set up. Last thing I take off.
3. Mirror is very exposed so I have fixed posts around so its protected when fitting the light shroud.
4. You will need a trolley setup to move it around unless you have another person to help.

Hope this information is of some use.

Cheers

Rick

[dave brock]

Any updates on this scope Rick?

Dave