Semi-Newbie with Questions about dobs

I've owned a Meade ETX90 for about a year and I have a little aperture fever. I want a dob that is within my budget. The two front runners are the new Orion XT10 Intelliscope and the Discovery 10". Maybe even the Discovery 12.5 if I can swing it but I like the Intelliscope Push-To feature--always a trade off. Orion claims the primary in their new scope is American and Pyrex and that seems to be a big deal with Discovery. I've read the S&T myth article about the differences, or perceivable lack of, between plate glass and Pyrex.

What are the pros and cons of the metal tube and the sonotube? What is a sonotube actually made of? What about a truss system?

Any and all information is welcomed!

Damn clouds!

I may get flamed for this, but I had a plate glass Orion XT10 and now have a 16" soda lime (glass) Discovery. I have a Telrad, a Rigel, and a red dot finder, a straight through finder and a right angle finder (I know you did not ask about finders, but just in case :-) ) . They all work good. I don't have preferences. They give (or gave) me great images and the finder or tube material really had no bearing on what I see. When I first looked at M13 in the 16" I had no thoughts what-so-ever on the material that the tube was made of or if I had found the general area in a Rigel or a Telrad!

You can't make a bad choice - enjoy what ever you pick.

Michael

In answer to part of your question, a Sonotube(R) is used as a form for concrete. Sonotubes are made from fibers that are spirally wound and laminated with a special adhesive. For more info, check http://www.concreteacc.com/sonotube.asp.

My first real telescope was an 8-inch Orion Deep Space Explorer purchased in 1997. The tube is a Sonotube, and I still have it. I have drilled into it to add accessories. I have two counterweight kits on it, which I mounted with wood screws.

Later I added the Orion Sky Wizard 3 Electronic Finder & Sky Catalog and an Orion kit for adding encoders to the telescope base.

I would imagine the Sky Wizard is the forerunner of the current XT "intelligence." I didn't use the Sky Wizard much at the time, and I thought the documentation was awful. The new hand controller looks a lot classier.

If I had known the sky better in those days, I might have gotten more use out of the Sky Wizard. It really helps if you know about the top dozen brightest stars you can see from your location. We still take this dob out for public sky watches and when we travel. Also it has made a great white light solar scope (you need a filter) for looking at sunspots.

If I had to replace it today, I would consider the Orion XT10 (metal tube) as well as the Sonotube brands. I would feel less comfortable drilling the thin metal, but the things I added, such as handles and a nav knob, are now part of the XT telescope and the tension adjustment may have eliminated the need for counterweights.

Today I would definitely go for a 2-inch focuser.

Gerry
State College, Pa.

Ah, the semi-annual sonotube vs metal tube debate.

I've owned them both. I like them both. A lot of "facts" about how one is better than the other and you should certainly consider these inputs before buying. They may indeed matter to you. Here's what I think I know about both:

Metal:

1. It dings, but not terribly
2. Touch it and you will get a thermal reaction inside the tube (I've seen it at the ep)
3. Your tongue will stick to it in the winter (I haven't done this yet)
4. Magnets stick to it (very handy for all sorts of things, see pic)
5. Easy to chop up and modify

Sonotube

1. Doesn't ding so much
2. Less thermally sensitive (not thermally sensitive)
3. Your tongue probably won't stick to it
4. Magnets won't stick to it
5. Easy to chop up and modify

The sliding altitude hubs on the Discovery are nice, but the magnets on my XT10 are just as easy to manage. I, personally, would not choose a scope based on a metal or sonotube OTA, but others might.

For the rest of the questions, I can't add a lot. A 12.5" tube dob is big, very big. But it is worth the extra 2.5" if you can afford it and it doesn't keep you from observing as much as possible.

Discovery vs Synta vs Guen Sheng will be debated until the cows come home. I wouldn't kick any of them out of bed for eating cookies. Buy one and never look back. The joy is in the looking.

Clear skies,

Tom

Attached Image:

>>>Orion claims the primary in their new scope is American and Pyrex and that seems to be a big deal with Discovery.

From their website:

"The XT10 IntelliScope features exquisite optics: a 10" (254mm) parabolic mirror (1200mm focal length, f/4.7) figured from low-expansion, U.S.-made Pyrex glass for superior thermal stability."

The Pyrex is made in the US, the mirror is not.

>>>>I've read the S&T myth article about the differences, or perceivable lack of, between plate glass and Pyrex.

The thermal differences are real and do have an affect on performance during cool down. With smaller mirrors this is not so important but it is a real effect and with large mirrors pretty important.

>>What are the pros and cons of the metal tube and the sonotube? What is a sonotube actually made of? What about a truss system?

I have two metal DOBs and one sonotube DOB. The metal ones look nicer, the paint is really nice looking and makes a finished looking scope. But as someone pointed out, metal tubes have thermal issues. On a cool night with good seeing, just touching the OTA of my XT-8 to move it will cause a small tube current which is easy to see in the star image and takes about 30 seconds to die out. Not good for high power work. Gloves will resolve this.

Truss Tube are for portablility, make a big scope fit in a vehicle. The 10 inch F5 scopes are a good size to fit in a car and be portable, 48 inch OTA will fit across the back seat and the 35lb OTA is not too much to easily carry through a door.

Anything bigger, it would be good to see in person before purchase. A 12.5 inch F5 Discovery scope is a big scope and a handful to move. THe 10 inch F6 is similarly heavy and long.

The size changes how often the scope gets used. Certainly the 12.5 inch shows more DSOs and more detail than the 10 inch but it is not a big factor and it is a great deal more difficult to deal with. Most nights it is the 10 inch that comes goes out the door.

jon