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What's the largest size amateur dob available?

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#26 BluewaterObserva

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Posted 17 June 2013 - 03:07 PM

I have a 30" on a GEM in my obs. I thought I wanted a 1 meter, but the 30" really was already bite'n off more than I could really chew. :)

#27 robininni

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Posted 17 June 2013 - 09:19 PM

I have a 30" on a GEM in my obs. I thought I wanted a 1 meter, but the 30" really was already bite'n off more than I could really chew. :)


Whoa! When I think 30" reflector, I immediately thing Dobsonian. That's got to be one heck of a GEM--an Orion Atlas no doubt?:lol:

#28 BluewaterObserva

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Posted 17 June 2013 - 10:38 PM

I believe it is one of the largest aperture scopes, GEM mounted, still in use in the world.

800lbs of counterweight on there by the way. :)

If your curious:
http://www.cloudynig...4111141/page...

#29 Bill Weir

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Posted 18 June 2013 - 12:39 AM

This is the f/5 25" that I was out visiting tonight at the school observatory. I was supposed to be showing a visiting school group around the observatory but unfortunately the weather didn't cooperate. That metal tube is 9' long. Counter weights are in the 800lb range also.

Bill

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#30 Bill Weir

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Posted 18 June 2013 - 12:42 AM

This is what it looked like in the beginning before it was painted and Jack Newton was still dragging it around on a trailer to dark sites. This was before he donated it to the school.

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#31 kfrederick

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Posted 18 June 2013 - 05:28 AM

A 40 inch f3 the eyepiece is under 100 inches above the primary .The diameter is not the pain it is the length of the OTA A 39.4 inch supper max blank is not bad price .

#32 LivingNDixie

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Posted 18 June 2013 - 11:05 AM

There are four 36in Obsessions in existance. One is owned my Larry Mitchell in Texas. One is owned by a guy in Birmingham Alabama. I don't know where the other two are. These scopes are massive.

#33 Pinbout

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Posted 18 June 2013 - 09:19 PM

What about tom clarks 42? I'd like to look thru that scope since lockwood worked the mirror.

#34 FJA

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Posted 11 July 2013 - 06:04 AM

There are four 36in Obsessions in existance. One is owned my Larry Mitchell in Texas. One is owned by a guy in Birmingham Alabama. I don't know where the other two are. These scopes are massive.


I'm fairly (though not 100%) certain that a guy here in the UK has got one.

#35 George N

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Posted 11 July 2013 - 11:21 AM

There are four 36in Obsessions in existance. One is owned my Larry Mitchell in Texas. One is owned by a guy in Birmingham Alabama. I don't know where the other two are. These scopes are massive.


One Obsession 36 is (was?) owned by a guy in New Hampshire. He brought it to Stellafane 2 or 3 years, where I had a chance to look thru it and talk to the owner. Some other folks who know him have told me that he now has it in an observatory at his home.

I kept thinking of this scope as "Dobasaurus Rex"! It was huge. However, it was possible for one person to set up. Like the Obsession 30's, it is on wheels that are rotated out of the way when observing. It also cranks down after the truss poles are in place to hang the UTA on while standing on the ground. The owner had added a finder scope on an additional pole so that it could be used while standing on the ground. The 36 was transported in a trailer with a ramp backdoor, so to get it out, you just push it down the ramp. To get it back in the trailer, there was a small electric winch at the front of the trailer (powered by the tow vehicle's battery). Attach the cable to the scope - pull it up the ramp.

The owner told me that he was thinking of going back to a 20-inch, but he never did. He also said that owning a scope this size was "a lifestyle choice, like getting married or joining a monastery."

I've seen a number of other 28 to 32 inch Dobs that I consider designed to be easier to set up than the Obsession 36..... but that is a relatively old scope that now seems 'slow' at F/5.

#36 derangedhermit

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Posted 11 July 2013 - 11:44 AM

Anyway, Mike Clements is building and is almost done with his 70 inch reflector which is out at Steve Dobbs home/land. Here is a link to a post in February on that from my blog.

If my eyes do not deceive me, that's a 9-"point" (disc) cell.

#37 dan_h

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Posted 11 July 2013 - 12:09 PM

A 40 inch f3 the eyepiece is under 100 inches above the primary .The diameter is not the pain it is the length of the OTA A 39.4 inch supper max blank is not bad price .


I believe Kim Colter has a 40" Dob in a permanent home in Missouri. I don't know the f ratio.

dan

#38 Achernar

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Posted 11 July 2013 - 12:11 PM

Massive does not begin to describe any 36-inch Dob, not when you see the eyepiece 15 feet above the ground. :shocked: I've only seen one Dob in person that was that big. It was at the 2006 Okie-Tex starparty and to say the least it stood out among a forest of large Dobs that were on the site. Seeing how tall of a ladder was needed to reach the eyepiece, I opted not look through it. I work off of ladders and at heights for a living, I do not like climbing in the dark, not after falling off a ladder, not once but twice. In both case I was very lucky that I didn't get seriously hurt, or worse. I have heard of folks falling off a ladders while peering through big Dobs too.

Taras

#39 turtle86

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Posted 11 July 2013 - 12:26 PM

What about tom clarks 42? I'd like to look thru that scope since lockwood worked the mirror.


It had great views even before Lockwood worked on the mirror. On one cold memorable night Thor's Helmet looked almost three dimensional with near photographic detail.

#40 TechPan6415

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Posted 22 July 2013 - 01:44 PM

Anyway, Mike Clements is building and is almost done with his 70 inch reflector which is out at Steve Dobbs home/land. Here is a link to a post in February on that from my blog.


That....is....
insane!

The largest scope I ever looked through was a 36" Coulter Optical monster at Riverside in the early 90's. I saw color in M8 and it was pretty memorable. I figure until I get a permanent home I am good with my 16", a 24"-30" might speak to me more clearly if I have an observatory to put it in.

But 70"...wow, I could not imagine what those views would be like.

#41 Gord

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Posted 22 July 2013 - 02:31 PM

I will also mention Normand Fullum. When I spoke to him in the late spring (at the AstroCATS show), I think he said the biggest one he had done was 50 or 60". Pretty big for a private user! :grin:

But in the 30-40" range, my understanding is that he has done a number of them.

Also of great interest were the new cellular mirror blanks he was just getting. These are not the fused blanks you can see on his site, but actual cellular ones like Dream offers. The 12.5" was only 7 lbs!!! :shocked: The biggest he had of these though was (only) 20". :cool:

The wheels have been turning ever since!

Clear skies,

#42 John Kuhl

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Posted 22 July 2013 - 04:30 PM


I would think if you had enough money you could get as big of a scope as you want. If I ever hit a $100 million on the lotto I'd buy a 100 incher.

Best, John

#43 northernontario

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Posted 22 July 2013 - 06:40 PM

web page Normand Fullum telescopes :cool:


I had the pleasure of meeting him this year at the Oakville gathering.

He had a 36 inch mirror with him. Uncoated but ready to go.

He also had some of his hand crafted wooden scopes with him.

Incredible workmanship.

He stated that he would have a 36 inch at Starfest in August. There will be a few of our very own members there as well giving presentations.

I hope I can get out to this event, I can afford a trip there more than I can afford a 36 inch telescope.



jake

#44 FJA

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Posted 22 July 2013 - 06:45 PM

I would think if you had enough money you could get as big of a scope as you want. If I ever hit a $100 million on the lotto I'd buy a 100 incher.

Best, John


I'd do something like that. That and move to the SW USA or the Australian outback where the air is dry and the skies clear...no point spending that kind of money on a scope living where I live. A handful of clear nights each month isn't so bad with an 18" but anything colossal would require good skies.

Btw the guy in the UK I thought had one of the Obsession 36" scopes actually has a 30".

#45 amicus sidera

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Posted 23 July 2013 - 06:08 PM

But 70"...wow, I could not imagine what those views would be like.


I can.

Extremely limited field and, for the most part, seeing that turns all that light into pudding.

Pickering had it right all along.

Fred

#46 hbanich

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Posted 24 July 2013 - 12:37 AM

Not necessarily. I've observed with 48 and 90 inch scopes and they both produced wonderfully sharp views when the seeing settled down. When the seeing boiled up the views were still mesmerizing so I think optical quality will be the main determining factor in how well the 70 inch will perform. The mechanics of the scope are nearly as important, and I'm sure we'll start to hear more once the 70 inch begins its observing career.

#47 amicus sidera

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Posted 24 July 2013 - 08:22 AM

Very true, Howard; during times of excellent seeing the views would be fantastic. I'd think that the owner of such an instrument would of necessity be quite limited as regards siting the instrument; most of the interior U.S., save for the desert Southwest at altitude, would be out of bounds, due to the lack of sub-arc-second seeing on a regular basis.

Fred

#48 davidpitre

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Posted 24 July 2013 - 08:42 PM

I think those who dismiss these very large scopes have likely not used them. I have used the McDonald 82" with both good and not so good seeing. Regardless, the views were staggering. Such a scope does not at all require sub arc-second seeing. True, with poor seeing, it's not worth the effort, but then neither is my 4" in my book.

#49 omahaastro

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Posted 24 July 2013 - 09:15 PM

I'm not sure I'd want to go much narrower than the 2/3rd degree max FOV I've got with my big gun today though. I still enjoy looking at some more expansive objcts. These mega scopes are sporting some mini fields of view.

#50 CounterWeight

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Posted 25 July 2013 - 10:00 AM

Would love to see an update on that whopper!






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