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Equipment Discussions >> Reflectors

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dpwoos
Pooh-Bah
*****

Reged: 10/18/06

Loc: United States
Re: Advice on large dob? new [Re: CoreyinOR]
      #6140845 - 10/16/13 12:47 PM

Quote:

I currently have a 10" Newtonian for imaging and I am thinking of getting a large "portable" truss based dob for visual. I'm considering either a 16" or 18" scope.

The Hubble UL18 scope is really appealing to me since one person can assemble,disassemble and move it. It looks like it stores easily which is another consideration.

I was only able to find one review, so I'm not sure how many of those actually have been sold. Also, there seems to be some debate on quality of the sandwich mirrors produced by Hubble Optics.

Please let me know if you have any advice for a first time large dob buyer.




Have you hung out with a dob of this size? Are you confident that you know what you will be getting at the eyepiece, and what that will cost in effort?

If not, then join your local astro club and observe with these folks. On the other hand you could just go for it and sell the scope if it doesn't live up to your expectations, which is one reason why the used scope market is very active.


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TechPan6415
sage
*****

Reged: 07/29/12

Loc: Aspen, Co
Re: Advice on large dob? new [Re: Achernar]
      #6140944 - 10/16/13 01:36 PM

My criteria was super simple, get as big a scope as I could carry the components down stairs by my self, have it take up minimal room in a small apartment when stowed and view comfortably at the zenith while standing.

I did not need to drive 100+ miles to a "local" star party or "Local" club to check out some guys million pound 18" Obsession Classic or million dollar 18" UC to figure out that I was either going to be building the scope I needed or taking my chances on a UL-16. I might have went for the UL-18 if they offered it at the time because it is still a manageable beast as far as I am concerned.

It's just not that hard to look at the specs and figure out what you want, obviously bigger is better, but to a point in terms of managing it.

I did my research and as far as I am concerned, I totally nailed what I wanted, it's not hard to figure out.


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GeneT
Ely Kid
*****

Reged: 11/07/08

Loc: South Texas
Re: Advice on large dob? new [Re: Achernar]
      #6141047 - 10/16/13 02:35 PM

Quote:

A 15 or 16-inch will got into many cars, and for someone who is about six feet tall no ladder will be needed even while looking at the zenith. A 18 or 20-inch needs a six foot step ladder, and a 30-inch required a tall ladder.




One's height and upper body strength figures into this decision. I have a friend who is 6' 3". He hefts an 18 inch Dob as easily as I do with my 12.5 incher. I am 5' 10". We both view flat footed at zenith. My 6' 3" friend also has an easy time loading, unloading, and setting up his telescope. A few years ago, I thought an Obsession 18 inch Ultra Compact would be perfect for me. Even with its F4.2 mirror, I needed a two step stool to view at zenith. Being older, standing on a stool looking up, at odd angles, causes me to loose my balance. The 18 UC also was hard for me to pick up and load. Its handles rested about two inches from the floor. I had to make an upward jerking movement, which I felt would ultimately cause me to pull something in my back. Therefore, I had to use the wheely bars and ramps to load the telescope. Wheely bars and ramps take up a lot of room in a vehicle. I originally thought that I would not have to use them. Where I finally ended up in all this was with my 12.5 inch Portaball. I have a small three wheeled transporter so all I have to do is lift the telescope up about six inches and onto the transporter, then into my vehicle. The upper assembly is encased/nests in the sphere and easily rides on one of the seats.

There are many factors to consider regarding the size of a telescope. Sometimes we don't get it right the first time. Sometimes our circumstances change such as where we live, or our physical health. Due to these kind of factors, I have bought and sold several telescopes over the years. I am happy where I ended up.


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cw00
member


Reged: 08/16/11

Loc: La Mesa, CA
Re: Advice on large dob? new [Re: GeneT]
      #6141139 - 10/16/13 03:18 PM

There are many things to consider when taking on a large dob. One thing is whether you are going to use it in your backyard most of the time or you are going to transport it to a dark site. If using primarily in the yard, how bad is light pollution there? The UC design may be compact but it may not be ideal for your observation site if there is plenty of stray light coming in from all directions. When considering a classic model, the size of the mirror box will be one deciding factor. I can fit my 20" Obsession classic in my Honda CRV but it is pretty tight. And the mirror box clears my front door by a hair. So I measured everything multiple times before placing an order. In the end, I have no regrets with all the hassle because the view of the large dob at a dark site is simply priceless.

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Dick Jacobson
scholastic sledgehammer


Reged: 12/22/06

Loc: Plymouth, Minnesota, USA
Re: Advice on large dob? new [Re: TechPan6415]
      #6141264 - 10/16/13 04:44 PM

Quote:

Quote:

Regarding Hubble Optics, a friend ordered a 16" and was very unhappy with the mirror. He had it tested by a local expert who said it was the worst mirror he had ever seen. Hubble replaced it, but my friend is still not very happy with the scope, optically and mechanically.




What specifically was the issue that made it the "Worst mirror he had ever seen"?



The Strehl ratio was 0.3 as I recall, meaning it was nowhere near diffraction limited.


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dpwoos
Pooh-Bah
*****

Reged: 10/18/06

Loc: United States
Re: Advice on large dob? new [Re: Dick Jacobson]
      #6141289 - 10/16/13 04:55 PM

Not surprising that the mirror isn't the only problem, as it would be quite incredible for a business to get everything but the mirror right, and the mirror so spectacularly wrong.

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TechPan6415
sage
*****

Reged: 07/29/12

Loc: Aspen, Co
Re: Advice on large dob? new [Re: Dick Jacobson]
      #6142539 - 10/17/13 09:44 AM

Quote:

Quote:

Quote:

Regarding Hubble Optics, a friend ordered a 16" and was very unhappy with the mirror. He had it tested by a local expert who said it was the worst mirror he had ever seen. Hubble replaced it, but my friend is still not very happy with the scope, optically and mechanically.




What specifically was the issue that made it the "Worst mirror he had ever seen"?



The Strehl ratio was 0.3 as I recall, meaning it was nowhere near diffraction limited.




I suppose for the price, a couple of bad ones are going to appear. Mine seems to do well especially when seeing and collimation are dead on. I might still get Swaze to test it and if it could benifet from a refigure, that too.

It still puts me way less than an price of an Obsession UC of which the mirrors are simply too darn heavy for my to carry up and down the steps of my apartment, especially when covered in snow in Winter.

I wish people would lay off this company a bit, Tong is great to deal with and frankly, if it were not for the size and weight of the UL16, I would have passed on getting a scope altogether since for what I had in mind, only a 16" or larger would do, but within the tight limits of my use and storage situation.


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