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mount options for observatory

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#1 Blackmyst

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Posted 17 June 2009 - 09:11 AM

Hi everyone

I'm currently building an observatory (I'm tired of lugging my stuff around ;) ), and I've reached the age old question of "which GEM"...

As my focus is towards DSO astro-photography accuracy and stability is something to keep in mind. Currently I have an LX90 8" which is a great scope, the tracking however... :)

I started looking at the usual suspects, CGEM, G-11 and such and was strongly leaning towards the G-11 (with the aftermarket worm-gear) which new would be $3500. All this would allow me to mount the lx90 and my imaging equipment easily (around 33 lbs - OTA is 31 lbs according to manual).

but could I do better for another say $500-$600 ?

My kids love astronomy, but the fights are driving me nuts, which will more than likely lead to another scope (I'm watching the AT8RC with great interest, but I'm waiting to see when and how much the 10" and 12" will be...

so the field now changes dramatically, I'd rather purchase something once, than having to repurchase later.

Am I losing my mind here, or is this entirely possible running the lx90 and say a AT12RC on a dual mounting bar on the same GEM? My guess would be that they would weigh in the region of 65 lbs (the CF tube lowering the weight of the RC) - which would mean the mount would have to able to take 90lbs+ load to still maintain accuracy.

I've had a look at the G42 obs mount, which seems like it should be able to take the weight, but what are the options?

regards

Jon

#2 tim53

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Posted 17 June 2009 - 12:15 PM

I've mounted a 6" f/5 Jaegers, C-8, and a Megrez 80mm, with cameras on 2 of these at a time, all on a Casady Triad bar on my used (~$4500 off astromart) Tak NJP Temma PC (pre temma 2) with no problems before.

-Tim.

#3 Blackmyst

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Posted 17 June 2009 - 06:29 PM

Thanks for the recommendation :)

the big ? is the weight of an additional scope (I have no idea the weight of a 12" RC) - from looking at others, they seem to be between 40-60lbs...??

the NJP can take 70lbs which even at 40lbs for the additional scope would be pushing the limit for visual, your load I gauged at +- 45lbs, which is perfect for AP.

Do you have an idea what a 12" RC would weigh?

regards

Jon

#4 Phil Cowell

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Posted 17 June 2009 - 06:48 PM

The G-11 will not take 90# + even with the new worm gear. If you wanted Losmandy you'd better look more towards the Titan. For AP you'll normally target about half the mounts capacity. Nearer the limit if your using it for visual. As the RC's are primarily designed as Astrographs find the weight of the scope, add all your guidescope, camera and other stuff in to the mix and double it. Now you have the ball park for the mounts capacity you need.
Phil

#5 lineman_16735

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Posted 17 June 2009 - 10:08 PM

Just to add to Phil's post. With the G-11 you should in fact stay closer to 30-35 lbs for imaging. The NJP, AP 900/1200, MI-250 etc, the weight ratings stated have imaging in mind. So an NJP with 65lbs of gear should be no problem for imaging.

#6 Blackmyst

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Posted 18 June 2009 - 12:09 AM

thanks - that was the reason for moving away from the G-11, and towards something else... trying to calculate the weight is one unknown currently, I'm waiting to see how the AT12RC fairs when it comes. I'm using a ballpark figure of 40lbs for the OTA but don't know...

will the NJP handle that much weight? I see the rated figure I managed to find was 70lbs, if it were just the RC it'd be fine, but with the lx90 as well? (or am I completely off-track here...)

regards

Jon

#7 David Pavlich

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Posted 18 June 2009 - 07:49 AM

Is your intention to mount the 8" SC and the 12" RC together? If so, I would ask why? With the imaging capabilities of a 12" RC, the 8" SC would be an Albatros. A better, and lighter combination would be the RC and a small refractor in the 80-90mm range. Makes a great guider and can be used for widefield imaging.

However, if it were me, I'd have the 12" RC and piggyback something like an Orion ST80 for your guider and image with the RC exclusively. No weight problem and easy to balance.

That combination would allow something like a CGE or G11 as your mount. However, if it's in your budget, then look at the used market for the NJP, MI250, Titan, etc.

David

#8 Blackmyst

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Posted 18 June 2009 - 09:37 AM

Hi David, sounds weird I know, in a word - kids, at least they'll be able to see what dad is "looking" at, AND I won't have to fight them for telescope time ;D

you're right an APO would be a better option, thanks for the advice on the used market, I've been having a look but nothing yet.

I could of course not mount the 2 together (which has been raising it's head..) and place the lx90 on a tripod for the kids.

#9 GShaffer

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Posted 18 June 2009 - 10:15 AM

If funds are keeping you from going larger keep your eyes open for a shaefer mount.....plenty heavy duty enough 100 lbs or so capacity and have byers gears.....if you want goto I have seen several adaptations around.....

#10 Luigi

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Posted 18 June 2009 - 11:28 AM

Kids. Let them use the scope on a separate mount. Then you can bug them to see what they're looking at.

#11 tim53

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Posted 18 June 2009 - 01:38 PM

I second (or forth?) the recommendation that you mount the LX90 and 12" RC separately. And if you're putting them in an observatory, a roll-off roof rather than a dome.

I have a 12.5" f/23 Classical Cass that I built a teak 1/4" plywood tube for, that is 5' long. I've never weighed it, but it's probably 45 pounds or so.

I've used it on the NJP before, and though it's within the mount's weight handling capability, that 5' tube is quite a lever arm, so I haven't put that scope on it since I picked up a used EM-500 last summer. A 12" RC might be comfortable on the NJP, though, mainly due to its shorter tube. But I wouldn't mount anything else of any size with it (the refractor guidescope is a good suggestion).

The NJP handles my 6" f/10 Jaegers refractor - also with a wooden tube - quite well, though. I tried once to mount the refractor, c-8 and megrez on the mount at the same time, and didn't like it much.

But my Triad bar is heavy to start with, plus it has a "TGAD" saddle for aiming a guide scope that's pretty heavy, and another adjustable saddle that I made for the Megrez. All told, I think the triad bar without the OTAs weighs about 35 pounds!

-Tim.

#12 DeanS

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Posted 18 June 2009 - 01:50 PM

Give the kids their own mount, the LX90 sounds pefect, as far from your imaging set up as you can. The last thing you want is for someone to mess around with yours after you get it set up, balanced and tweaked just right.

Oh and I suggest buy the very best mount you can afford now, it will save you money in the long run from constant upgrading.

#13 Blackmyst

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Posted 18 June 2009 - 03:22 PM

thanks everyone :)

the design for the obs is a roll off, I started with the " a dome would be nice" train of thought then realized the financial director (my wife :) ) wouldn't permit a great big round thing in the garden :D So the plan grew, a thatched gazebo (or lapa as we call it here - south africa) some wooden decks and somehow just happened to include the observatory - still not sure how that happened ;) The kids can then use the lx90 on one of the decks. And I can bug the hell out of them :D (thanks Luigi)

I discovered the true OTA weight of the lx90, and it sure as hell isn't 31lbs as they print in the manual, it's actually 18lbs - sorry guys, I have a rather large wooden wedge which adds significant weight (when lugging the entire setup around), which made it seem feasible...

now, if it would only stop raining I'd be able to start on the damn thing :mad:, I need to use large amounts of concrete as my land is sloped, so the obs and pier can be separately supported with concrete pillars.

It's my own fault really, bought an illuminated reticle to specifically use this week, and took days off work to do it... oh well :)

Dean, I follow the same philosophy, by as much as you can afford now (without going into debt), you save in the long run.

So, now that that is resolved, I should be looking at something in the region of 70lbs load.... time to start saving like hell I suppose :D

Has anyone had a chance to use the G41/G42? I know the G42 is over this weight, just curious - it seems almost too good to be true...

regards

Jon






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