GoTo Mounts

[chris]

I'm thinking about putting my 10" dob on a Goto mount, just wondering if anyone has any suggestions?
I would love a losmandy G11, however it is a bit far out of my budget.
Can anyone tell me what the difference is with the celestron CG5GT and the skywatcher eq6 skyscan?

Cheers
Chris

[Radar]

Hmm, what kind of DOB is it Chris. I'm not sure why DOBs are rarely used on GEMs. Because DOBs are so much bigger than standard newtonains, there may be an issue. I think GEM type mounts are more deisnged to house smaller scopes such as SCT's, Newts and Refractors.

Wind catching a DOB mounted on a GEM could causes other issues. I'll look into this a bit more Chris and see what I can come up with.

For the noobs - GEM = German Equatorial Mount
DOB = Dobsonian Telescope

[chris]

Thanks for the quick response Radar, i have a Guan Sheng GS-880.

[Radar]

No problem Chris.

Okay, firstly I don't think that brackets are made for mounting a DOBs on a GEM, and there is a reason.

DOBs are not really designed to be held by the middle of their tubes. The tubes are so large, that attaching these scopes by the centre of their tubes could cause some kind of flexure or damage. Because of the long focal length, any flexure would put your collimation out by quite a bit.

It seems that as a rule of thumb, DOBs are always mounted from the bottom.

Swinging a DOB around on a GEM may also put parts of the scope dangerously close to the ground.

I think this is an interesting topic. I will learn more and post it.

Regards

Ray

[AstroTasmania]

Just a reminder that telescopes commonly referred to as Dobs, dobs, are in fact Newtonian optical systems (Newtonian telescope) supported on an Alt/Az mount named after John Dobson an American amateur astronomer who came up with this easy to make, low cost method of mounting the scope. This has done a lot to popularise astronomy. GEM mounts are more costly and significantly more difficult to make.

In fact, most Newtonian telescopes were mounted on a GEM mount as a general rule, or on large home made fork mounts. Dobsonian mounts are a relatively new concept.

A Dobsonian mounted Newtonian is the correct description for the telescope.

"Dob" is also spelt with a capital 'D'

Clear skies...

[chris]

Thanks for that AstroTasmania, sounds like i will be able to mount my Dob on a GEM.:cool!:

Any suggestions of which GEM would suit my Dob?


Cheers
Chris

[Radar]

One thing I can add here is that any mount you use should be overkill. The more weight your scope can hold, the more sturdy it will be. Wind will catch a Dob easily. But also vibrations from the ground may causes the scope to jitter for long periods.

I only have experience with the Losmandy G11. Good mount. There are others here that can probably shed more light on this than me though.

[AstroTasmania]

There is one thing to strive for when mounting a telescope, size of mounting. The bigger the better. In fact few amateur telescopes are ever mounted on a mount that is bigger than the optical tube, which is how it needs to be. Just look at how the professional telescopes are mounted.

The problem for amateurs is the cost of such a mount and its portability - or lack of.

The 16 inch telescope at Mt Canopus (image below) is on a mounting very much bigger than the optical tube, it weighs tons and it is rock solid. Half of the mounting is below the floor level. I have used this scope a lot over the years. The level of stability is needed for serious scientific imaging & spectroscopy. A small GEM will carry a big scope, but it will flutter like a leaf in a breeze as soon as you touch the focuser, making it useless for photography etc.

Newtonian's were always GEM mounted long before the Dobsonian mount came along, look in some of the old S&T magazines. The tube does not flex because it was held within solid tube rings widely spaced attached to a very solid Dec plate.

Apart from the top line GEM mounts, Takahashi, Astro Physics, Anssen Technologies etc. the largest GEM on the amateur market seems to be the Chinese made EQ6, which is sold under various brand names.

My Anssen Alhena GEM makes the EQ6 look small, but then it is not really portable, even though it can be transported, the head alone weighs in at 35 kg.

So, the Dobsonian mount now fills a need for our various sized Newtonian's, due to it's design and size in relation to the tube it is supporting. It has its downsides when it comes to long exposure photography but for visual work, it is ideal.

I grew up building my own telescopes because it was too expensive to buy them, and as I progressed from the typical 6" up the size scale, I built many types of mounts, some of which were bigger than the optical tube, but were not portable, nor did it need to be. It seems that there is always a compromise. Lots of fun and learning on the way though.

Clear skies...

[beren]

I own a CG5ASGT , with the scopes I use its a surprisingly stable and accurate mount , its stated to have a 35 pound payload limit but I would be reluctant to use one with a 10" Newtonian loaded on it. The EQ6 mount has a 40 pound limit but weighs {mount head and tripod} 23kg, probably about 12kgs more then the CG5, I would go for the EQ6 to support the tube of a 10" reflector.The CG5 mount pivot points are a lot lower then the EQ6, with my scopes the tripod legs in certain angles pointing to zenith can be hit or be in the way, that would be a major pain with larger long tubed OTAs. I think you can get a EQ6 goto mount{along with the CG5ASGTand HEQ5} for under 2 grand now , quite amazing I think considering the capability it offers. It would be great to own a G11 but these cheaper mounts shouldn't be underestimated, for photographic applications I've been surprised how well my CG5 tracks granted I'm using short focal lengths but with some tweaking and patience these mounts give great visual and good imaging results at a good price :thumbsupmate:

[chris]

I mentioned these two mounts (CG5 GT & EQ6) as both Celestron and Skywatcher mount 10" Newtonians and sell them into the market, so i thought that if they can sell it in the market then it should be alright to put my 10" Dob on one of these mounts.
I am restricted to some degree as l currently only have a budget of $2,000 and both of these mounts are under that ($1,249 for the CG5 GT) from Andrews Communications and ($1,999 for the Skywatcher EQ6) from Bintel. I think even the Orion Atlas EQ-G is another cheaper GEM on the market, although not to sure where they can be bought from here in Aus.

The reason i want to mount my Newtonian onto a GEM is so i can get into astrophotography, however it sounds that it might be very difficult to perform this with a 10" Newtonian on a cheaper GEM.
It might be better to save up some more $$$$ and purchase a SCT for my astrophotography and keep my Dob as a visual scope.

Cheers
Chris

[beren]

Bintel sell the Orion Atlas {EQ6 variant} and the smaller HEQ5 {HEQ5}.

[Radar]

I have heard many good things about these types of mounts. They appear to be good value. At the end of the day, if they are doing the job then great.

[AstroTasmania]

The EQ6 is the largest mount, regardless of how branded/named.

Clear skies...

[scorpius]

I am running a SW880 Newt on an EQ6Pro V3 with home made tube rings with the tube balance point central in the rings with no problems. SW880 (10") weighs in at 12.5 Kg. The EQ6 is rated at 25kg The 2 balance weights5.1kg ea, are just enough mounted on the end of the pipe.

I assume the total loading includes the scope and the counterweights. In which case a scope of 12.5kg is the maximum size for an EQ6 Warning if the mount is not set up correctly before using, the scope can foul the tripod legs.

[chris]

G'Day Scorpius,
Thanks for your response.
I have been doing lots of research into this as i am well on my way in getting enough cash together to purchase the eq6 mount.
The research has resulted that the eq6 mount can handle up to 8" refractors and 14" reflectors, although i doubt that either of these size telescopes would be able to handle astrophotography on this mount.
The eq6 mount can handle payloads of 25kg which i have been led to believe that this means everything on the saddle and does not include the counter weights.
Does anyone know if this is correct? :hmm:


Cheers,
Chris

[Radar]

Warning if the mount is not set up correctly before using, the scope can foul the tripod legs.

Ouch.

I remember when I first started using a GEM. It was as recent as last year, I had very little idea of how they worked. I had to read the instruction manual ten times to absorb the setting up of it. But over the first few occasions of setting it up I didn't lock the counterweight on the bar and it slid down or I forget to lock the clutches and my scope would go swinging. Luckily I was always there to catch things, phew! Last thing I want to see is peices of mirror under my mount.

I have read a lot of good things about those EQ6 mounts. They are very popular and good value.

[AstroTasmania]

Hi,

Just came across this fellow's site, which looks as if he has taken his 10" Newtonian off his Dobsonian mount and put it on his EQ.

http://www.research.rutgers.edu/~koushik/Rutgers/Equipment.html

I would not use anything less than an EQ6 for a 10" Newtonian reflector.

Traditionally,the majority of Newtonian reflectors scopes were mounted like this, before John Dobson came along with his alt/az box.

Clear skies...

[scorpius]

All my probs have been my own !! They are a big learning curve (See also Polar Alignment with Guidescope item) with the poor Chinlish manual
This morning I nipped up to the Big B warehouse and got some 5.5" pine planking and made three shoes for the EQ mount Countersunk a hole in each for those ballerina toes of the tripod. It will will take quicksand for it to sink now.:welldone:

[chris]

Just been looking at another forum and see that Mike Salway has put his 12" GSO Dob on a EQ6 mount.

http://www.iceinspace.com.au/forum/attachment.php?attachmentid=23725&d=1171916475


Cheers
Chris

[Radar]

although i doubt that either of these size telescopes would be able to handle astrophotography on this mount.


Chris don't forget that if your astrophotography ambitions are to shoot digital, that means you can get yourself a self guiding ccd camera, which means no guidescope needed. All you would need is the ccd camera itself which guides and images at the same time.

So if you are getting to the mounts limit with size and weight, use a self guiding camera and cut out the guidescope part.

[chris]

G'Day Ray,
I plan to go digital, was just going to get something like the canon 350d.
I don't know anything about ccd cameras.:noob:
How do they work?
How do they autoguide?

Cheers
Chris

[scorpius]

Chris don't forget that if your astrophotography ambitions are to shoot digital, that means you can get yourself a self guiding ccd camera, which means no guidescope needed. All you would need is the ccd camera itself which guides and images at the same time.

So if you are getting to the mounts limit with size and weight, use a self guiding camera and cut out the guidescope part.

One important thing I should have mentioned about using large Newts on the EQ6. Whilst everyone agrees its the way to go, one factor does enter the equation when using it for astrophotography. "Stability"; remote shooting of the camera is essential when you have 1.2 metres of 10" scope up there it does have some tremour when touching it and in strongish winds can make the system unusable. Probably for photography a refractor is the better option in the field. Roger G may have some comments on this?

Cheers Dave.

Anyone going down to to Dryandra ASWA do this coming weekend (WA) I am

[Radar]

G'Day Ray,
I don't know anything about ccd cameras.:noob:
How do they work?
How do they autoguide?


Hi Chris, I know very little about CCD's to. Shevill and others here can probably shed more light on this issue. Though the concept of a self guiding camera is quite straight forward. Basically the ccd has two chips inside the head. One chip for imaging, and the other chip for guiding.

You can see in this image how there are two chips, the smaller chip is for the guiding. Using a camera like this does away with the need for a guidscope, greatly reducing the weight of your setup.

There is also off axis guiding to consider as well.

359



Anyone going down to to Dryandra ASWA do this coming weekend (WA) I am

I might be there Dave. I will keep you posted.

[rogerg]

The reason i want to mount my Newtonian onto a GEM is so i can get into astrophotography, however it sounds that it might be very difficult to perform this with a 10" Newtonian on a cheaper GEM.
It might be better to save up some more $$$$ and purchase a SCT for my astrophotography and keep my Dob as a visual scope.

For astrophotography (as I'm sure has been mentioned in this thread already) you just want the biggest mount with best PE, least backlash, and autoguiding capability you can afford.

Personally I like your idea of saving up for the SCT and keeping the Newtonian as a Dob. A 10" Newt on a GEM is not what I descdribe as easily portable, just as a 12" SCT is not easily portable. A 10" Dob is definitely easily portable.

A fork mounted SCT makes a great astro photography platform, assuming it's one of reasonable quality (again: capacity, PE, backlash, autoguiding).

Roger.