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clock-drive eq mount with 30 pound payload?

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#1 anthonysf

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Posted 12 March 2013 - 06:55 PM

I'm considering buying an Explore Scientific "David Levy Comet Hunter" 152 mm Maksutov-Newtonian reflector to replace my 150 mm Orion Newtonian reflector. But the ES Mak-Newtonian weighs 25 pounds, probably 30 pounds with eyepieces etc., and that would be too heavy for my Orion EQ-3 mount.

I would like to find a non-computerized equatorial mount with a clock drive that could carry a 30 pound load. I enjoy finding objects in the sky the old fashioned way, and I don't want to lug around the extra weight of a 12 volt battery for a go-to drive. The non-go-to equatorial mounts seem to max out at a 20-pound payload.

Any advice or suggestions would be greatly appreciated.

Anthony Barreiro
San Francisco, CA, Turtle Island

#2 jrcrilly

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Posted 12 March 2013 - 07:00 PM

GPD2

#3 Don Taylor

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Posted 12 March 2013 - 08:59 PM

Losmandy GM-8

#4 orlyandico

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Posted 12 March 2013 - 09:04 PM

old used non-GoTo Atlas. Cheapest solution by far.

#5 anthonysf

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Posted 13 March 2013 - 12:13 AM

Thanks for the suggestions!

#6 mistyridge

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Posted 13 March 2013 - 12:51 AM

Any Losmandy mount can be used in a non goto way because they use slip clutches on both axis. Just push to. The G11 would work best for a 30lb scope

#7 Geo.

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Posted 13 March 2013 - 09:44 AM

As you are not doing AP you might consider the Vixen GP. Conservatively rated at 22 pounds, I was recently surprised by its stability carrying a Celestron C9.25. The GP was was on a Vixen tall wood legged tripod with no extension of the legs. I have found the C9.25 to be intolerable on the similar Celestron ASCG-5 (rated at 30#) with the 2" steel legged tripod.

#8 orlyandico

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Posted 13 March 2013 - 10:13 AM

George, remember that rust bucket garage GP we ended up bidding over on ebay years back?

I put my C9.25 on that mount for a while.. I was personally not too happy with it. I will allow that it was more stable than a 127 Mak on a Porta.

Maybe that's good enough for some people..

#9 Kendahl

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Posted 13 March 2013 - 12:19 PM

According to Explore Scientific's website, the Comet Hunter optical tube weighs only 15.4 lbs. Have you asked their tech support if this includes finder, rings and eyepiece? Even if not, they shouldn't take it over 20 lbs. Any 30 lb mount should do fine for visual and wouldn't be unreasonable for photography given the Comet Hunter's short tube and focal length.

The Comet Hunter, without a mount, costs $1,000. For $1,400, Orion will sell you an 8" f/4.9 Newtonian on their Sirius mount. I know you don't care about GoTo, but the combination is a bargain.

We have the 6" f/8 Newtonian that Orion used to sell on their Skyview Pro mount and still sell as a Dob. In our experience, its optics are very good. Since it is an f/8, collimation is easy. Is that what you intend to replace? If so, I question whether you will gain anything unless you go to a significantly bigger aperture.

Note that faster reflectors are more difficult to collimate and, if they are pure Newtonians, need a coma corrector.

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#10 Phil Sherman

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Posted 13 March 2013 - 03:56 PM

The Comet Hunter, without a mount, costs $1,000. For $1,400, Orion will sell you an 8" f/4.9 Newtonian on their Sirius mount. I know you don't care about GoTo, but the combination is a bargain.
.....
Note that faster reflectors are more difficult to collimate and, if they are pure Newtonians, need a coma corrector.

Kendahl


Orion's 8" on the Sirius mount is a bear for AP. The mount requires guiding and when you add a guiding gear to the 8"; you'll be approaching the weight limit of the Sirius. I gave up on mine when the scope, camera, guide scope and guide camera totalled just under 30lbs and upgraded the mount to an Atlas.

Imaging is possible with that heavy a load but you need to get everything perfectly balanced (requires three separate axis balances) and will need a wind shield if there's any breeze at all.

A much better choice for imaging would be a 6" Newtonian on the Sirius mount. It would be interesting to price this out using Orion's "build a scope" option.

Phil

#11 SeattleScott

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Posted 13 March 2013 - 11:09 PM

My 10" F4.8 reflector weighs 24lbs with rings and 10x50 finder. So I would be highly surprised if the 6" F4.8 Comet Hunter weighs more than my 10". I know the Comet Hunter has a corrector lens and dew shield, but isn't it made of lightweight carbon fiber?

I use the CG5 for my 10" and it does just fine as long as it isn't windy. The sheer size of the tube tends to catch the wind.

#12 Kendahl

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Posted 14 March 2013 - 12:18 AM

Orion's 8" on the Sirius mount is a bear for AP. The mount requires guiding and when you add a guiding gear to the 8"; you'll be approaching the weight limit of the Sirius. I gave up on mine when the scope, camera, guide scope and guide camera totalled just under 30lbs and upgraded the mount to an Atlas.

If your guide scope is a long refractor mounted piggyback, I can see how you got up to 30 lb. For that much weight, I agree that you need an Atlas or something comparable like a CGEM.

However, that much weight is no longer necessary. Orion's Magnificent Mini Autoguider package weighs 1.5 lb. A DSLR camera weighs 1 lb. Dovetail bar and scope rings add no more than 3 lb. Since the 8" optical tube weighs 16.5 lb, that makes the total only 22 lb. The biggest difference between the Orion 8" and the Comet Hunter is the Orion's longer, fatter tube. It will be more susceptible to wind.

Orion no longer sells a separate 6" optical tube; 8" is the smallest. Astronomics has in stock an Astro-Tech 6" f/4 tube that weighs 10 lb and costs $299. A better scope would be Vixen's 8" f/4 R200SS. Because its tube is aluminum, it weighs only 12 lb. However, the price is $1,500. Any f/4 Newtonian will require a coma corrector and meticulous collimation.

Another possibility is an 8" Celestron Schmidt Cassegrain. Weight is 12.5 lb and focal length with the reducer/corrector is 1,280 mm. The new EdgeHD is better but far more expensive. My one gripe about their 8" scopes is that the visual back is designed for 1.25" eyepieces. To get a 2" back, you need to go to 9.25" which is heavier and more expensive. You would need an Atlas or a CGEM to carry a 9.25" SCT.

One of the guys in our local club is successfully doing AP with an 11" Celestron Schmidt Cassegrain at f/6.3 on a CGEM mount. He uses a piggyback guide scope and camera instead of an off axis guider. Total weight must be close to the CGEM's 40 lb limit.






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