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Can you attach a dobsonian newt ota to a gem?

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#1 user8881

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Posted 29 March 2011 - 01:09 PM

For example, could I put my Orion XT10 classic on a Meade LX75 or equivelant mount? I don't see why not, it meets the weight requirement, but I don't know if there is something different in how a newt is constructed when it's made for a dob mount or a gem that would make incompatable. I really enjoy mt XT10 but I can help but wish for tracking.

#2 Doug76

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Posted 29 March 2011 - 01:28 PM

You can indeed, but that particular scope is too much for that mount to handle.
IMO you'd need at least an Atlas/CGEM sized mount to do that scope justice.
It isn't all about weight rating, the length of the scope plays into it too.

#3 JadeSmith

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Posted 29 March 2011 - 02:36 PM

I wouldn't put my Z10 on my CGEM. No way. :thumbsdown:
It might be able to handle it, but still...

#4 Magellan

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Posted 29 March 2011 - 04:08 PM

Yeah thats a heavy scope, I wouldn't put it on my CGEM either.

#5 Eddgie

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Posted 29 March 2011 - 06:39 PM

Remember that you also need to incude the weight of the tube rings and the dovetail.

A agree with everyone else that it is a lot of weight for an LXD-75.

The other issue is that when GEM mounted, the eyepiece of a Newtonian can get in some odd positions. To counteract this, you should get some kind of rotating system for the tube. You can buy rotating rings (very expensive, but work beautifully) or you can modify the tube with rollers so that it can move in regular rings.

The advantage of tracking is very real, and if that is what you are after, I encourage you to persue it, but I recommend a beefier mount.

If you ONLY need tracking (and not go-to or setting circles), you can use a Poncet table. Expensive to buy, but people build their own too.

#6 Mirzam

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Posted 29 March 2011 - 06:49 PM

The other important consideration is the mirror cell. In all likelihood the XT10 uses a mirror cell with clips to hold the mirror at any orientation. However, many dobs use slings to support the mirror in which case the supports only work for altitude movements in a single plane (i.e. straight up and down). You could not mount such an OTA on a GEm without modification.

JimC

#7 mclewis1

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Posted 29 March 2011 - 08:38 PM

If you look back (20+ years) to when vendors regularly put big newtonians on gems you'll notice a few things ...

1) They were just about always on piers not tripods. The piers usually had wheels and leveling bolts.

2) The gems used were generally quite a bit heavier than the mounts like LXD75s or CGEMs, even the "lightweight" models had 1" shafts. Most regular weight gems for 8" and larger scopes had 1.25-1.5" shafts, this is CGE to CGEPro class of mount.

#8 Arbacia

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Posted 29 March 2011 - 08:44 PM

A friend is using a 12" Newtonian on a EQ6. He is very proud.

#9 KWB

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Posted 29 March 2011 - 09:05 PM

For example, could I put my Orion XT10 classic on a Meade LX75 or equivelant mount? I don't see why not, it meets the weight requirement, but I don't know if there is something different in how a newt is constructed when it's made for a dob mount or a gem that would make incompatable. I really enjoy mt XT10 but I can help but wish for tracking.

Hi

The XT10 OTA combined with this Meade mount will flunk your test in short order and will not pass muster. If you want a tracking Dob,other possibilities/tracking platforms exist other than using a mammoth sized GEM,and that is what you need if using a GEM.

Choose wisely. :scratchhead:

#10 Doug76

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Posted 29 March 2011 - 09:14 PM

A friend is using a 12" Newtonian on a EQ6. He is very proud.


I bet he is!

It's doable, but I bet it's shaky. With a 12" it's not only the weight but the length taxing an EQ6.
With a 10", you are within the weight limit of an EQ6/Atlas/CGEM class mount, but the length will give you fits.

#11 avarakin

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Posted 29 March 2011 - 11:40 PM

At some point I mounted my Antares 40lb 10" dob OTA on LXD75 and it worked without much trouble. The reasons why I am not using this configuration anymore:
1. the whole setup is very heavy, there is no way to pick it up and carry few feet as possible with the dob
2. I have to stand while observing, where as with dob I can seat for all altitudes
3. setting up and breaking up takes more time with GEM
4. some tube rotation method is reguired
5. not clear if overload may cause system failure in future

So in the end I just went back to dob and so far not looking back. One day I may build tracking platform.

Alex

#12 Skylook123

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Posted 30 March 2011 - 12:14 AM

You could deal with the eyepiece rotation cheaply with Wilcox rings, but the balance in DEC will be a real stresser on larger newts. The balance point is back near the mirror, so that eyepiece end will be way out there, as mentioned already.

The biggest mass produced item I can recall seeing was the 16" Meade Starfinder Equatorial, but the mount was made to set lower than you can get with a CGEM or EQ6 tripod; there are reasons that these setups with newtonians are so rare, and SCTs fill the bill. Chasing the ol' eyepiece is an acquired taste.

Easier to mount the dob on an equatorial platform.

#13 eric_zeiner

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Posted 30 March 2011 - 02:10 AM

If you have not experienced an under mounted scope, it is not pretty and can be rather frustrating. It will even get to the point where the mount/scope combo will set up its own harmonics and never stop shaking. Even though there are some mass produced 10"rs that are on a CG5 type mount, it has got to be a hot mess.

#14 idealistic

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Posted 30 March 2011 - 10:39 AM

I use an 8 inch newt on a GEM, the trick is balance.
Spend the time to get everything balanced, and mark the ideal spot on the dovetail, and the ideal orientation of the OTA in the rings and youll be fine. When mine is perfectly balanced the eyepiece is almost straight up in the air in the "home" position, but when do you observe in that orientation anyway? Certain situations require you to rotate the tube in the rings, but not as often as you might think.

My only issue is rarely being able to sit down, which may be a problem for some.

#15 user8881

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Posted 30 March 2011 - 01:55 PM

Thanks for all the info, I guess I'll abandon my dream of having a big newt on a gem. I remember a while ago companies like Meade offered big newts on gems, up to 16" iirc. Now I see why they are no longer made. I'll probably look into an Orion xx14g when I'm ready for a bigger scope since it has a tracking mount. I don't care about goto or AP, but I love my high power views of planetary nebulas, globulars etc making tracking desireable.

#16 Cotts

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Posted 30 March 2011 - 11:17 PM


I had a 10" Lightbridge + Parallax rings on an EQ6 and, later, a G11 with no problems. Careful balance is vital, though.

The cell on the Lightbridge is ideal for this because it supports the mirror all around the circumference. Any dob with a sling won't work at all, as was said upthread...

Dave

#17 Asimov

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Posted 01 April 2011 - 12:01 AM

I think it depends on the circumstances. About a month ago I purchased the SW collapsible 14" with Synscan GOTO. The OTA weighs in at exactly 25KG.

I bought this in the hope that the tracking was good enough for planet imaging, but it's not. My next recourse was to try mounting the standard SW OTA on my EQ6. I didn't even bother trying that scenerio seeing the EQ6 is rated at between 20-25KG.

Anyway the end result was to see me making a light weight OTA for the 14" optics to mount on the EQ6. Total weight of the OTA is just over 14KG & the EQ6 holds it easily & tracks nicely. As for lever arm action due to OTA length: Not a concern for me as it'll be going in an observatory.

Since taking this photo a couple of weeks ago, I have taken out 8 or so inches off the height of that portable pier.

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#18 SPACEMAN

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Posted 01 April 2011 - 02:36 AM

Indeed if you place the telescope on a EQ6 mount, normally it will hold. a EQ6 can be very strong. But LX75 no.....

#19 hottr6

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Posted 01 April 2011 - 05:51 PM

I started with a used Byers 812 GEM, picked up an el-cheapo Meade Starfinder OTA and with some Parallax Rings, I was up and running. The Byers is definitely underwhelmed by this OTA.

"Chasing the eyepiece" is problematic. I did rig up some "rotating rings" that still require me to unlatch the Parallax' to rotate the OTA. No biggy; it's habit now.

I'm contemplating purchasing some 16-18" optics and building my own OTA for the Byers. That is a big step and may overwhelm my highly modified ScopeBuggy, in which case a more permananent solution would be required. Mo' $$$$. :(

Nevertheless, it is a great feeling to walk away from an object and return many minutes later to find the object still perfectly centered in the FOV.

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#20 Asimov

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Posted 01 April 2011 - 11:23 PM

Nice work there. Yes the Byers could stand a way bigger OTA than that.

#21 Patrick

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Posted 02 April 2011 - 10:54 PM

could I put my Orion XT10 classic on a Meade LX75 or equivelant mount?



Celestron still sells their C10N-GT which sits on the CG5 mount which is pretty much the same as the LXD75. So they must think it's okay. I've used that configuration before and found it to be somewhat marginal.

The main difficulty in putting so much weight on the mount comes when trying to focus the scope. The slightest touch can cause vibrations which take a few seconds to dampen out. Touching your face against the eyepiece can do the same thing.

The other thing is that a 10" Newt on an EQ mount can be just plain difficult to use. The contortions required to get to the eyepiece can sometimes be painful, depending on where the scope is pointed.

Patrick

#22 avarakin

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Posted 03 April 2011 - 01:16 AM

Meade was also selling LXD75 with 10" reflector on top of it, so that means it is designed to carry such load.

Alex

#23 Asimov

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Posted 03 April 2011 - 02:19 AM

The SN-10 weighs 13.61 kg. (30 lbs.) So there's some indication. Heck, that's nearly the weight of my 14" OTA! Heavy little sucker!

#24 Jon Isaacs

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Posted 03 April 2011 - 03:57 AM

could I put my Orion XT10 classic on a Meade LX75 or equivelant mount?



Celestron still sells their C10N-GT which sits on the CG5 mount which is pretty much the same as the LXD75. So they must think it's okay. I've used that configuration before and found it to be somewhat marginal.

The main difficulty in putting so much weight on the mount comes when trying to focus the scope. The slightest touch can cause vibrations which take a few seconds to dampen out. Touching your face against the eyepiece can do the same thing.

The other thing is that a 10" Newt on an EQ mount can be just plain difficult to use. The contortions required to get to the eyepiece can sometimes be painful, depending on where the scope is pointed.

Patrick


Patrick:

The fact that Celestron will sell you a 10 inch Newtonian on the CG-5 mount doesn't mean it is a good choice, it just means they are willing to sell it... This is what it looks like to me:

A few years ago, I bought a pair of rings so I could mount my 10 inch F/5 GSO Dob on my CG-5 ASGT. I was (and am) using the mount with a 8 inch F/5 Newtonian and it works quite well. I set it in my telescope work area, mounted the 10 inch F/5 onto the CG-5, it took 33lbs of counter weights to balance it, and that was without eyepieces. I could tell then and there that from a stability standpoint, the mount was overloaded, it wobbled and vibrated at very touch. NO WAY JOSE...

As far as the Newtonians from 30 years ago, I have a couple, an RV-6 and a 12.5 inch F/6 RG. Certainly the pier mount is the right design for scopes like this. Those old mounts were robust but crude and everything is heavy, the OTA is about 100lbs, it takes 85lbs of counterweights, total weight is about 300lbs. The rotating rings, they are nice, it gives nice views.

My suggestion to anyone considering building or buying a larger Newtonian on a GEM, if you haven't used one, find a way to spend a few hours with one. Patrick and others point to the difficulty in using these scopes. Viewing positions can be awkward....

There is a reason they call it the "Dob revolution." Dobsonians are simplier, more stable, much more comfortable to use. If you are looking over the fence and seeing the greenery of tracking that the GEM provides, it's kind of soggy over there. Take a careful look before you commit.

Jon

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#25 Patrick

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Posted 03 April 2011 - 05:05 AM

Patrick:

The fact that Celestron will sell you a 10 inch Newtonian on the CG-5 mount doesn't mean it is a good choice, it just means they are willing to sell it...



Yes, I totally agree. Sorry if I wasn't clearer when I said it was 'marginal'.

The guy who owned the C10N-GT was an older man, and by the time he got the scope setup he was too tired to use it or enjoy it. In addition to the ergonomics of using a Newt on a GEM in general, a 10" Newt on a GEM often requires the use of a ladder or stepping stool to get to the eyepiece.

If one wants to add tracking to a Dob, the best solution might be an equatorial platform.

Patrick






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