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Equipment Discussions >> Reflectors

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paulr57
member


Reged: 01/09/13

Loc: Asheboro, NC
truss vs solid tube dob
      #5835888 - 05/02/13 09:44 AM

I've been trying to find a comparison between a truss and solid tube dob. Other than weight considerations are there any advantages between the 2 designs?

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JimP
Pooh-Bah


Reged: 04/22/03

Loc: South Carolina
Re: truss vs solid tube dob new [Re: paulr57]
      #5835912 - 05/02/13 09:58 AM

A solid tube will keep the heat waves and extraneous light out of the optical path best.
From a stricktly aestheic point of view, and I am only speaking for me, I think a solid tube would look better and has the Potential to help transform the Dobsonianb into a far more professional looking telescope (if that even matters to you or anyone el;se). I did say For Me.
I awaiut the criticism and the points which favor open tubes with cloth shrouds.
JimP


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DJCalma
member


Reged: 01/17/13

Loc: Northern California
Re: truss vs solid tube dob new [Re: JimP]
      #5836004 - 05/02/13 10:50 AM

Solid tube: Hot water heater looking, heavy, bulky, ugly, unprofessional, heat wave trapping, inefficient, ancient cumbersome tube.

Truss: Sleek, professional, efficient, cool air flowing, practical, compact, versatile, modern, aesthetically attractive design.


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planet earth
Carpal Tunnel
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Reged: 09/07/10

Loc: Ontario Canada
Re: truss vs solid tube dob new [Re: DJCalma]
      #5836020 - 05/02/13 10:56 AM

Quote:

Solid tube: Hot water heater looking, heavy, bulky, ugly, unprofessional, heat wave trapping, inefficient, ancient cumbersome tube.




I don't know? the Cave Astrola telescopes look pretty fine to me.!
Sam


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okieav8rAdministrator
I'd rather be flying!
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Reged: 03/01/09

Loc: Oklahoma!
Re: truss vs solid tube dob new [Re: DJCalma]
      #5836023 - 05/02/13 10:57 AM

It's a size issue as much as anything. Once you start looking at telescopes 15" and bigger, tubes get massive. Big truss dobs break down for easier storage and transport. Discovery makes split-tube dobs in the 15"-17.5" sizes, and I think maybe a 12" too. A friend of mine has both 15" and 17.5" Discovery dobs, and in my opinion, they are way more of a hassle to deal with than my 20" Obsession. I just ramp it up into the bed of my pickup truck and go--no heavy or cumbersome lifting at all. But, that's just me--to each his own.

Edited by okieav8r (05/02/13 10:59 AM)


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dscarpa
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Reged: 03/15/08

Loc: San Diego Ca.
Re: truss vs solid tube dob new [Re: paulr57]
      #5836092 - 05/02/13 11:32 AM

I ordered a Teeter 11" F/5 Solid Tube Series mainly because it will hold collimation better than a truss dob. 99% of the time the scope will be used in my back yard with lunar-planetary my number one interest though I do enjoy DSOs too, the STS will have Sky Commander. An 11" F/5 is the biggest tube dob I would want to deal with. David

Edited by dscarpa (05/02/13 01:33 PM)


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aatt
sage


Reged: 07/26/12

Loc: CT
Re: truss vs solid tube dob new [Re: okieav8r]
      #5836094 - 05/02/13 11:33 AM

I have the Discovery 15" split-tube. Despite careful measurements prior to purchasing I found it took me quite some time to figure out how to get it into my Honda Accord-after initially giving up in frustration. It will barely fit.Glad I did not get the 17.5" I would be stuck at home! The LTA is very awkward and heavy and the UTA is not bad. I have arrived at a system for moving it. Set-up is 6 minutes including collimation now (it holds collimation very well).Despite these issues, I am very very happy with it. Going bigger would not be advisable unless you have a van, are really tall (6+) and a have really strong lower back. The only reason I bought this one was money-truss designs were hundreds of dollars more.

Edited by aatt (05/02/13 11:35 AM)


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Mike B
Starstruck
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Reged: 04/06/05

Loc: shake, rattle, & roll, CA
Re: truss vs solid tube dob new [Re: DJCalma]
      #5836098 - 05/02/13 11:35 AM

Quote:

Once you start looking at telescopes 15" and bigger, tubes get massive.



I'm with Rex on this... tho i'd have to say "go look at the tuber before you BUY one!" A 12" tube-Dob is massive, and many cars can't easily fit the common 12-inch tube across the rear seat. Even a 10-incher is beyond most EQ mount's ability to hold one steady enough for serviceable views (if such a mounting issue matters?). You know this, as it sounds like you already have the 10.

The Dob mounting also gets big+heavy fast beyond 10-inches. Check the manuf. weights on 10 vs. 12 inchers. Everyone will have their own threshold of what they'd consider "too big" for tubers, but the threshold that matters is how it seems to YOU!

Quote:

Solid tube: Hot water heater looking, heavy, bulky, ugly, unprofessional, heat wave trapping, inefficient, ancient cumbersome tube.

Truss: Sleek, professional, efficient, cool air flowing, practical, compact, versatile, modern, aesthetically attractive design.






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Achernar
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Reged: 02/25/06

Loc: Mobile, Alabama, USA
Re: truss vs solid tube dob new [Re: paulr57]
      #5836110 - 05/02/13 11:40 AM

No tube currents, because of the open mirror box and thin fabric shroud. And you can set up a 20-inch or even larger truss-tube Dob yourself. I can get my 15-inch into a car, impossible to do with a solid tube of the same aperture and focal ratio.

Solid tubes are less expensive, less affected by dewing and heat waves getting into the light path, and they don't need to be collimated everytime you set them up. A truss tube requires that the collimation be touched up when it's set up, but that only takes a minute or two with the right collimation tool(s). A solid tube also allows you to put extra finders, digital setting circle computers, and the like where ever you want. In the 10-inch and under range, it makes more sense usually to opt for a solid tube, unless you require airline portability for the telescope.

Taras


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okieav8rAdministrator
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Reged: 03/01/09

Loc: Oklahoma!
Re: truss vs solid tube dob new [Re: Achernar]
      #5836169 - 05/02/13 12:16 PM

One thing I'll say about truss dobs holding collimation: If it isn't holding it well, there is a weak link somewhere that needs to be looked at and can be fixed. Once I identified my weak links, my Obsession scopes hold collimation extremely well. One problem I had was that the nuts and bolts holding the miror cell in the rocker box would loosen over time, so I replaced the lock washers and check the tightness once or twice a year. I also replaced the original sling with a Glatter sling, which I feel was a very worthwhile investment. And, I made a few minor mods to the cam levers on the upper tube assembley, and now they hold rock solid. No issues.

Checking the mechanics of any telescope now and then is always a good idea.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: truss vs solid tube dob new [Re: okieav8r]
      #5836289 - 05/02/13 01:17 PM

Quote:

It's a size issue as much as anything. Once you start looking at telescopes 15" and bigger, tubes get massive. Big truss dobs break down for easier storage and transport. Discovery makes split-tube dobs in the 15"-17.5" sizes, and I think maybe a 12" too. A friend of mine has both 15" and 17.5" Discovery dobs, and in my opinion, they are way more of a hassle to deal with than my 20" Obsession. I just ramp it up into the bed of my pickup truck and go--no heavy or cumbersome lifting at all. But, that's just me--to each his own.




I agree, it's a size thing. I think once one is thinking of a 12 inch or larger, a truss style is definitely worthy of consideration.

I do think tube scopes have fewer thermal issues so if one is thinking of a planetary double-star scope, a solid tube scope is probably the best bet.

JOn


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paul hart
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Reged: 06/01/04

Loc: Long Island, New York
Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5836723 - 05/02/13 04:50 PM

I agree anything larger than 12" that will be car transportable should be a truss design.

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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: truss vs solid tube dob new [Re: paulr57]
      #5836732 - 05/02/13 04:54 PM

There are pros and cons for each. I like the rule of thumb--up to 10 inches, solid tubes are fine. At 12 inches and larger, it is better to go with a truss.

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paulr57
member


Reged: 01/09/13

Loc: Asheboro, NC
Re: truss vs solid tube dob new [Re: GeneT]
      #5837297 - 05/02/13 09:28 PM

Thank you for the responses! You've certainly clarified this for me. I was worried about stray light but it seems an easy fix with a shroud if needed. Fortunately for me I don't have much to worry much about this in my yard. I live fairly rurally and have no really close neighbors.

Again thanks for all the responses!

Paul


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JMW
Pooh-Bah


Reged: 02/11/07

Loc: Nevada
Re: truss vs solid tube dob new [Re: paulr57]
      #5837340 - 05/02/13 10:01 PM

Even if you don't go huge a 12 - 16 inch well built truss dob will have a movement with steadiness at the eyepiece that exceeds any solid tube mass market scope. I enjoy the views in my Z12 tube but the solidness and settling time on our Obsession 20 F5 is way beyond the quality of experience on the dob I spent about $650 on.

I think a 12 inch water heater style tube dob is about the most bulk anyone will put up with. I think the dobstub kits are a good way up upgrading the experience if you are happy with the optics in your tube dob. Used truss dobs come up used all the time. If you are lucky something within driving distance will pop up. People hate to ship large dobs when selling used.


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Daniel Mounsey
Vendor (Woodland Hills)
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Reged: 06/12/02

Re: truss vs solid tube dob new [Re: paulr57]
      #5837485 - 05/02/13 11:47 PM

Quote:

I've been trying to find a comparison between a truss and solid tube dob. Other than weight considerations are there any advantages between the 2 designs?




Paul,

I think there have been some serious misunderstandings on the pros & cons of a tube vs. truss, particularly regarding visual quality. From a portability aspect, a truss is certainly common among apertures larger than 10", and this is understandable, however, when it comes to visual accuracy, a solid tube is far superior than a truss for several reasons.

Regards


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JMW
Pooh-Bah


Reged: 02/11/07

Loc: Nevada
Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5837513 - 05/03/13 12:09 AM

I agree that the rigidity of the optical system can be better on a quality solid tube dob. If the tube is giving much larger altitude bearings and a higher quality rocker box than you get with the particle board imports, the solid tube dob can give an excellent experience. I have no doubt that the Teeter 8 or 11 inch solid tube dobs are excellent. Notice that Teeter doesn't have solid tube dobs larger than 11 inches listed on his website.

With the proper mirror support a truss dob can maintain the collimation from horizon to zenith. Replacing a simple fabric sling with a Howie Glatter cable sling has made a major difference on our clubs' Obsession 20 inch f/5. You can put in a laser and move the scope from horizon to zenith and the laser stays on target. Faster f/3 to f/4.2 scopes also have shorter trusses which should reduce balance and sag on the UTA when close to the viewing the horizon.


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nicknacknock
professor emeritus
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Reged: 02/20/12

Loc: In a galaxy far far away...
Re: truss vs solid tube dob new [Re: paulr57]
      #5837604 - 05/03/13 02:45 AM

Quote:

Thank you for the responses! You've certainly clarified this for me. I was worried about stray light but it seems an easy fix with a shroud if needed. Fortunately for me I don't have much to worry much about this in my yard. I live fairly rurally and have no really close neighbors.

Again thanks for all the responses!

Paul




Paul,

You night also want to get a night shield to place opposite the focuser. You want to reduce stray light as much as possible as it is a contrast killer.

CS,

Nicos


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dave brock
professor emeritus


Reged: 06/06/08

Loc: Hamilton, New Zealand
Re: truss vs solid tube dob new [Re: paulr57]
      #5837623 - 05/03/13 03:32 AM

The biggest advantage I've found with solid tube dobs (homemade at least) is the relative ease in making the tube rotatable to bring the eyepiece to a comfortable position. For that reason I went with solid tubes up to and including 16" F/5. 10" and larger scopes I make also have the tube break in half for easier transport. The tube not rotating is about the only thing I don't like with my 20" truss dob.

Dave


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okieav8rAdministrator
I'd rather be flying!
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Reged: 03/01/09

Loc: Oklahoma!
Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5837702 - 05/03/13 06:56 AM

Quote:

however, when it comes to visual accuracy, a solid tube is far superior than a truss for several reasons.





You'll have to elaborate on that Daniel. I've owned and used all kinds of telescopes, and speaking from practical experience, I don't agree with that.


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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: truss vs solid tube dob new [Re: dave brock]
      #5837721 - 05/03/13 07:14 AM

Quote:

The biggest advantage I've found with solid tube dobs (homemade at least) is the relative ease in making the tube rotatable to bring the eyepiece to a comfortable position. For that reason I went with solid tubes up to and including 16" F/5. 10" and larger scopes I make also have the tube break in half for easier transport. The tube not rotating is about the only thing I don't like with my 20" truss dob.

Dave




along with ease of rotation is the ease of rebalancing, when I put my binos on my truss dob I have to add weight, with my tube just slide it...



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okieav8rAdministrator
I'd rather be flying!
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Reged: 03/01/09

Loc: Oklahoma!
Re: truss vs solid tube dob new [Re: Pinbout]
      #5837755 - 05/03/13 07:50 AM

that's a great looking telescope Danny. What is the tube made of?

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Mirzam
Post Laureate
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Reged: 04/01/08

Loc: Lovettsville, VA
Re: truss vs solid tube dob new [Re: dave brock]
      #5837775 - 05/03/13 08:17 AM

Dave-

I'm curious how you made your large tube dob (16") rotatable. I'm also thinking to build one like this.

JimC


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MikeBOKC
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Reged: 05/10/10

Loc: Oklahoma City, OK
Re: truss vs solid tube dob new [Re: okieav8r]
      #5837829 - 05/03/13 08:52 AM

Agree with Rex. I've never seen any appreciable difference in the views through truss or solid tube scopes. The optical alignment/collimation principles are the same either way.

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Pinbout
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Reged: 02/22/10

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Re: truss vs solid tube dob new [Re: okieav8r]
      #5837839 - 05/03/13 08:55 AM Attachment (14 downloads)

Quote:

What is the tube made of?




its a cardboard tube from shapesunlimited.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: truss vs solid tube dob new [Re: MikeBOKC]
      #5837913 - 05/03/13 09:37 AM

Quote:

Agree with Rex. I've never seen any appreciable difference in the views through truss or solid tube scopes. The optical alignment/collimation principles are the same either way.




I think it has to do with the effect of body heat drifting across the optical path. Shrouds do not block breezes with the same effectiveness as a solid tube.

I have noticed that since I converted my 12.5 inch F/4.06 to a truss, it doesn't handle the high magnifications viewing double stars the way it used to. It's not a collimation issue, the collimation doesn't shift.

One of these days to test this, I am going to replace the cloth shroud with a sheet of 0.060" ABS wrapped around to make a tube, it would be captured by the truss poles.

Jon


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dave brock
professor emeritus


Reged: 06/06/08

Loc: Hamilton, New Zealand
Re: truss vs solid tube dob new [Re: Mirzam]
      #5837923 - 05/03/13 09:43 AM Attachment (23 downloads)

Quote:

Dave-

I'm curious how you made your large tube dob (16") rotatable. I'm also thinking to build one like this.

JimC




Hi Jim.
The Tube rides in an octagonal cradle that has ends which are lined on the inside (against the tube) with felt. At each end of the cradle is a tube ring with Teflon tabs that rub against the cradle. The upper ring takes all the weight of the scope while the lower ring keeps the cradle in place when the tube is horizontal or being carried.
The best pic I have showing the system is this one of a 12" I made. The 16" is in the background btw.

Dave


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dave brock
professor emeritus


Reged: 06/06/08

Loc: Hamilton, New Zealand
Re: truss vs solid tube dob new [Re: dave brock]
      #5837945 - 05/03/13 09:56 AM Attachment (25 downloads)

An 8" with the same rotating tube system.

Dave


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okieav8rAdministrator
I'd rather be flying!
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Reged: 03/01/09

Loc: Oklahoma!
Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5837987 - 05/03/13 10:17 AM

Quote:

Quote:

Agree with Rex. I've never seen any appreciable difference in the views through truss or solid tube scopes. The optical alignment/collimation principles are the same either way.




I think it has to do with the effect of body heat drifting across the optical path. Shrouds do not block breezes with the same effectiveness as a solid tube.

I have noticed that since I converted my 12.5 inch F/4.06 to a truss, it doesn't handle the high magnifications viewing double stars the way it used to. It's not a collimation issue, the collimation doesn't shift.

One of these days to test this, I am going to replace the cloth shroud with a sheet of 0.060" ABS wrapped around to make a tube, it would be captured by the truss poles.

Jon




That would be an interesting experiment Jon. As for myself, I just don't see any real effect of body heat with my scope. I'm not much of a double star observer though, so it's hard to say.


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: truss vs solid tube dob new [Re: okieav8r]
      #5837999 - 05/03/13 10:26 AM

Quote:

That would be an interesting experiment Jon. As for myself, I just don't see any real effect of body heat with my scope. I'm not much of a double star observer though, so it's hard to say.




I think Daniel is a serious planetary/double star guy and observes with a group of LA "whackos" (as opposed to San Diego or Oklahoma whackos) who are really into it. They often have the good seeing and it's a constant shootout between some pretty awesome planetary scopes.

Jon


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5838123 - 05/03/13 11:15 AM

There are advantages to a truss--many actually:
1) lower center of gravity--more stable
2) much shorter rocker box--less shimmy and vibration
3) lower weight--OTA easier to pick up and move in a pinch.
4) easier to transport in a car--smaller and lighter segments
5) easier to remove primary mirror for cleaning
6) easier to create baffles above the primary to enhance contrast
7) larger altitude trunnions for less sensitivity to balance and superior altitude movement.
8) Better looking--more like a professional telescope. Often made of finely-finished wood.
9) easier to collimate accurately because you can get closer to the primary and secondary mirror surfaces or focuser to see a laser dot or shadow of the centermarker.


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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: truss vs solid tube dob new [Re: Starman1]
      #5838148 - 05/03/13 11:25 AM

Quote:

There are advantages to a truss--many actually:
1) lower center of gravity--more stable
2) much shorter rocker box--less shimmy and vibration
3) lower weight--OTA easier to pick up and move in a pinch.
4) easier to transport in a car--smaller and lighter segments
5) easier to remove primary mirror for cleaning
6) easier to create baffles above the primary to enhance contrast
7) larger altitude trunnions for less sensitivity to balance and superior altitude movement.
8) Better looking--more like a professional telescope. Often made of finely-finished wood.
9) easier to collimate accurately because you can get closer to the primary and secondary mirror surfaces or focuser to see a laser dot or shadow of the centermarker.




There is no doubt there are many advantages to a truss scope... But thermal management does not seem to be one of them.

Jon


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okieav8rAdministrator
I'd rather be flying!
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Reged: 03/01/09

Loc: Oklahoma!
Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5838167 - 05/03/13 11:40 AM

Quote:


I think Daniel is a serious planetary/double star guy and observes with a group of LA "whackos" (as opposed to San Diego or Oklahoma whackos) who are really into it. They often have the good seeing and it's a constant shootout between some pretty awesome planetary scopes.

Jon




What's "good seeing"?


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okieav8rAdministrator
I'd rather be flying!
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Reged: 03/01/09

Loc: Oklahoma!
Re: truss vs solid tube dob new [Re: Starman1]
      #5838178 - 05/03/13 11:44 AM

Quote:

There are advantages to a truss--many actually:
1) lower center of gravity--more stable
2) much shorter rocker box--less shimmy and vibration
3) lower weight--OTA easier to pick up and move in a pinch.
4) easier to transport in a car--smaller and lighter segments
5) easier to remove primary mirror for cleaning
6) easier to create baffles above the primary to enhance contrast
7) larger altitude trunnions for less sensitivity to balance and superior altitude movement.
8) Better looking--more like a professional telescope. Often made of finely-finished wood.
9) easier to collimate accurately because you can get closer to the primary and secondary mirror surfaces or focuser to see a laser dot or shadow of the centermarker.




Good points Don. My whole thing with the Truss vs. tube thing is that I just don't see a difference visually. My preference for truss scopes is simply that for large sizes, they are easier to deal with logistically, as your points well show.


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Jon Isaacs
Postmaster
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: truss vs solid tube dob new [Re: okieav8r]
      #5838215 - 05/03/13 12:05 PM

Quote:

Quote:


I think Daniel is a serious planetary/double star guy and observes with a group of LA "whackos" (as opposed to San Diego or Oklahoma whackos) who are really into it. They often have the good seeing and it's a constant shootout between some pretty awesome planetary scopes.

Jon




What's "good seeing"?




Half arcsecond or better? Don knows more about Daniel than I do. I agree that in the larger sizes, trusses are far more practical than Tube Dobs... No doubt about that...

Jon


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5838260 - 05/03/13 12:21 PM

There's no question that enhancing seeing conditions is a worthy thing for lunar/planetary/double star observers.

You can only do so much about the atmosphere (maybe by picking a site with good seeing), and the rest is in the scope. Thermal management is critical, which includes the ground under the scope as well as the scope. Even how you observe and where your body is relative to the scope matters.

For every other kind of observing, though, seeing can be less than perfect and still be OK. I've seen seeing so good the 12.5" was aperture-limited, but that's rare. It's less rare for my 5" Mak.
I've always paid attention to collimation and thermal issues in my scopes, so I get satisfactory performance from them just about all of the time.
That doesn't mean superb seeing isn't appreciated, though. Even we hard-core deep-sky observers see more details when seeing is superb.

So, pay attention to collimation and thermal issues and you will see better seeing more of the time. What side of the scope you stand on, or whether the scope is a full-tube or truss seems to be somewhat, uh, lower on the list of important issues.


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okieav8rAdministrator
I'd rather be flying!
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Reged: 03/01/09

Loc: Oklahoma!
Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5838649 - 05/03/13 03:58 PM

Quote:

Quote:



What's "good seeing"?




Half arcsecond or better? Don knows more about Daniel than I do. I agree that in the larger sizes, trusses are far more practical than Tube Dobs... No doubt about that...

Jon




Thanks Jon. My comment was more of a jab at the generally mediocre seeing I have to deal with in eastern Oklahoma. I have to get out into the western part of the state for better seeing conditions. I envy you for where you live and the much better seeing conditions that you have access to.


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Scanning4Comets
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Re: truss vs solid tube dob new [Re: okieav8r]
      #5838687 - 05/03/13 04:17 PM

Those scopes are a gorgeous work of art.



Cheers,


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Re: truss vs solid tube dob new [Re: okieav8r]
      #5838719 - 05/03/13 04:36 PM

Quote:

My comment was more of a jab at the generally mediocre seeing I have to deal with in eastern Oklahoma.



Ayup, that was clear enough.


Quote:

One of these days to test this, I am going to replace the cloth shroud with a sheet of 0.060" ABS wrapped around to make a tube, it would be captured by the truss poles.



Have thot 'bout this myself... shouldn't be too hard? Maybe even just at the upper half or third of the assembly, nearer the UTA. At least as a temporary set-up, to evaluate whether it was really worth pursuing...

For some folks, where their truss-Dob set-up for viewing planets has the prevailing winds blowing their heat back AWAY from the scope, perhaps it's not such an issue?

Last nite i was out, warm nite still from a hot (~92*F) day, thermals profoundly visible in the defocus (= "bright platter of squiggling worms" )... i could hold my hand up in front of the UTA & see the shadow of my hand+fingers in the "platter"- heat was pouring off like crazy & wafting upwards like "smoke"!

Yet- within mere seconds of removing my hand, the "smokey" thermals were gone. Entirely. Then, breathing forcibly thru the Dob's fabric shroud, i looked into the "platter" and saw a gradual waviness waft across the platter... then it, too, was gone. I can hardly imagine how "normal" breathing would even show up here... ... to say nothing of radiating body-heat.

Perhaps these "body-heat" effects are more pronounced (& of reasonable concern ) during winter months & greater delta-T's?... 99* human versus 33* ambient 12-inches away?... and/or combined with breezes pushing it into the lite-path? But 99* to ~80* over 12-inches... i remain not so much unconvinced, as unconcerned.

I'll take the 15" trusser over the tuber, ANY day! Thanks.


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Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5839049 - 05/03/13 08:59 PM

When you reach 15 or 16-inches, a truss is really the only practical option if you have to transport it. As for thermal issues, I don't see any disavantages at all, indeed my mirror cools off quite rapidly and I have an Obssession pattern mirror cell. I have a variable speed fan that I leave running all the time at low speed, without vibration problems and turning it off or on does not seem to affect the views. It's no worse or better than my 10-inch solid tube, also with a cooling fan.

Taras


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Re: truss vs solid tube dob new [Re: paulr57]
      #5839053 - 05/03/13 09:01 PM

One things for sure with my made extra heavy because it's an F/5 11" Teeter STS on the way I just best keep lifting those weights! David

Edited by dscarpa (05/03/13 09:10 PM)


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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5839411 - 05/04/13 12:40 AM

Thermal control is only one of several reasons a tube is superior for visual performance. Nevertheless it's good to see what people look like in reality.

http://www.youtube.com/watch?v=lSFwH0BVd3Q&NR=1
http://www.youtube.com/watch?v=sRnWCvxawrc&feature=related
http://www.youtube.com/watch?v=J7Xgbf3eZlM


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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5839608 - 05/04/13 06:07 AM

Quote:

Thermal control is only one of several reasons a tube is superior for visual performance. Nevertheless it's good to see what people look like in reality.

http://www.youtube.com/watch?v=lSFwH0BVd3Q&NR=1
http://www.youtube.com/watch?v=sRnWCvxawrc&feature=related
http://www.youtube.com/watch?v=J7Xgbf3eZlM




Similar views are possible just looking at the defocused image of a star in a telescope...

Jon


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Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5839749 - 05/04/13 09:11 AM

That's true Jon however, a binoviewer with a barlow and no eyepieces is far superior if you really want to conduct the schlieren test in its full splendor. Using an eyepiece is like looking under water without any goggles and it's a distorted picture. I've shown this to a number of observers and they were stunned at the clarity of so many disturbances in the optical path. You can clearly see little boundary waves above the surface of the primary when they exist. You can also differentiate jet streams, seeing, body and ground currents once you know what to look for. It's very dynamic.

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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5839891 - 05/04/13 10:58 AM

Quote:

That's true Jon however, a binoviewer with a barlow and no eyepieces is far superior if you really want to conduct the schlieren test in its full splendor. Using an eyepiece is like looking under water without any goggles and it's a distorted picture. I've shown this to a number of observers and they were stunned at the clarity of so many disturbances in the optical path. You can clearly see little boundary waves above the surface of the primary when they exist. You can also differentiate jet streams, seeing, body and ground currents once you know what to look for. It's very dynamic.




Interesting... A work we use schlieren for imaging shockwaves, it uses two 80mm F/11.3 Meade/Mizars telescopes and a high speed camera.



Jon


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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5839895 - 05/04/13 11:00 AM

Daniel,

Wow. And when you consider the trillions of things that live in the air---viruses, bacteria, seeds, spores (one puffball mushroom releases seven trillion of them), fungi, algae (some live in clouds), pieces of (or whole) mosses, caterpillars, aphids, spiders (some live at the top of Everest and their entire diet comes from junk in the air), flies, moths, beetles, mites...---well, it's amazing we can see anything with our scopes. If I set up next to our creek, I find mayflies and caddis flies on my mirror. Hummmm.... A certain tenacity is required for this hobby.

Dark skies.

Jack


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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5839990 - 05/04/13 12:00 PM

Quote:

Thermal control is only one of several reasons a tube is superior for visual performance. Nevertheless it's good to see what people look like in reality.

http://www.youtube.com/watch?v=lSFwH0BVd3Q&NR=1
http://www.youtube.com/watch?v=sRnWCvxawrc&feature=related
http://www.youtube.com/watch?v=J7Xgbf3eZlM






Those vids mean nothing. The only time I stick my hand in the optical psth is when I'm messing with the secondary.

There are no vids showing body heat from outside the optical path effecting the layers of air within the optical train.


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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5840080 - 05/04/13 12:54 PM

Quote:

It's very dynamic.




It is! In my post (somewhere above) where i described "smokey thermals", i was doing very similar to what Daniel described (no BVer, only "mono"), and it was quite the show- almost mesmerizing!

Even so, i had to make major efforts to have my body or breath induce anything visible in the "bright platter" of defocused starlight. I will continue to fiddle with this in the future- particularly after the scope has reached ambient temps... it is perhaps then that subtle influences could be better detected?

But my suspicion is that we're talking "subtle" here, at most, and then probably with steeper temp gradients between observer (98.6*) and the air within the lite-path of the scope.


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Re: truss vs solid tube dob new [Re: Mike B]
      #5840115 - 05/04/13 01:21 PM

Quote:

i had to make major efforts to have my body or breath induce anything visible in the "bright platter" of defocused starlight. I will continue to fiddle with this in the future- particularly after the scope has reached ambient temps... it is perhaps then that subtle influences could be better detected?






even if you had a fan sucking the air into the front, when I did my smoke test I had a hard time getting the smoke into the layers of air being pulled. most of the time the smoke was repelled.


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Re: truss vs solid tube dob new [Re: Pinbout]
      #5840196 - 05/04/13 02:22 PM

I run a small fan all the time that results in positive air pressure in the tube, exhausting at the top. Unless I put my hand in the optical path or breathe into the scope, I see no evidence of body heat in even an out-of-focus star image.

I have, however, seen heat rising from a group of people standing around and jawing about 10' in front of my scope, even though they weren't blocking the light.


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Re: truss vs solid tube dob new [Re: Starman1]
      #5840211 - 05/04/13 02:31 PM

Quote:

a group of people standing around and jawing about 10' in front of my scope




They're fine... just tell 'em to shut-up & stop breathing so heavily...



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Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5840268 - 05/04/13 03:07 PM

Jon,

That's a nice setup.


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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5840335 - 05/04/13 03:54 PM

Quote:

Jon,

That's a nice setup.




Thanks:

We use it with a mini-shock tube and the Imacon 200 Highspeed camera. The Imacon takes 16 frames and is capable of exposures of 5 nanoseconds with frame rates up to 200,000,000/sec though we normally operate in the 100 nano-second regime.

One thing to be aware of is that Schlieren imaging is qualitative rather than quantitative and shows the gradient in the index of refraction, you see the defocused component, you don't see the focused component. In that sense, the existence of "schliere" is only an indication that there is a defocused component but it does not indicate the level.

Jon


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Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5840407 - 05/04/13 04:43 PM

Jon,
Thanks for sharing.


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Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5840425 - 05/04/13 04:54 PM

Quote:

Quote:

That's true Jon however, a binoviewer with a barlow and no eyepieces is far superior if you really want to conduct the schlieren test in its full splendor. Using an eyepiece is like looking under water without any goggles and it's a distorted picture. I've shown this to a number of observers and they were stunned at the clarity of so many disturbances in the optical path. You can clearly see little boundary waves above the surface of the primary when they exist. You can also differentiate jet streams, seeing, body and ground currents once you know what to look for. It's very dynamic.




Interesting... A work we use schlieren for imaging shockwaves, it uses two 80mm F/11.3 Meade/Mizars telescopes and a high speed camera.



Jon




You're using telescopes... at work??! Lucky duck!


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Re: truss vs solid tube dob new [Re: Starman81]
      #5840459 - 05/04/13 05:15 PM

Yeah, but that's not even a 'shoot-out' they've got rigged... more of a stare-down.

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Re: truss vs solid tube dob new [Re: Starman1]
      #5840464 - 05/04/13 05:20 PM

Quote:

have, however, seen heat rising from a group of people standing around and jawing about 10' in front of my scope, even though they weren't blocking the light.




that's cool but that would be expected if they were under the optical axis.

This typical discussion usually centers around the person hovering over the focuser and how their body heat/breath effects the air in the optical axis.


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Re: truss vs solid tube dob new [Re: Starman81]
      #5840466 - 05/04/13 05:21 PM

I was imaging Jupiter one night (10" scope at F/45) and my daughter walked into my observatory and passed in front of my scope (but below the optical path). The amount of image distortion which occurred from her body heat rising in front of the optical path was unbelievable. The image of Jupiter changed from a fairly sharp clean image to a pulsating blob of heat waves. It was quite dramatic.

I would prefer a solid tube based on how beautiful the old Cave reflectors looked. I think a solid tube on a metal mount would be far more professional looking. I am not referring to anything being made today. I must admit I have seen no professional scopes made of plywood. If, portability is required then a truss tube may certainly be necessary.

JimP


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Mike B
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Re: truss vs solid tube dob new [Re: JimP]
      #5840497 - 05/04/13 05:42 PM

Quote:

I must admit I have seen no professional scopes made of plywood



What exactly constitutes a "professional scope"?
Mine's made by someone who makes (okay, *made*) Dobs for a living, and he was paid for the job, by its purchase.

Or, if one's scope or it's accomplishments are "published", does that make it professional?

I think a case could be made that "Obsession" & other Dobs made ("professionally") by those who receive a price for the build are "professional scopes".

I merely ask out of curiosity.

Quote:

The image of Jupiter changed from a fairly sharp clean image to a pulsating blob of heat waves. It was quite dramatic.



Do you recall what the temps/conditions were that nite? I'd be curious as to temp "gradients". The air being still may've also enabled such a constrained vertical flow of heat plumes... as might've the enclosure of your observatory.

Don's example might've been less prominent had it been one li'l girl at 10-feet, versus a whole gaggle of adults.


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Jon Isaacs
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Re: truss vs solid tube dob new [Re: Mike B]
      #5840546 - 05/04/13 06:21 PM

Quote:

What exactly constitutes a "professional scope"?




To my mind, professional implies a scientific research telescope, something a "professional" astronomer would use.

I doubt there are any that are made of plywood but then in the last 50 years, I would have to think there have been no new "professional" Newtonians and almost all new scopes are built using truss structures.

Regarding the effect of body heat. On s stable night with a fully cooled scope, it is easy to see the effect of momentarily touching a metal tubed scope. That's why I wear gloves if I am interested in working at high magnifications, just touching the tube to track will cause a tube current.

Jon


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Mike B
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Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5840566 - 05/04/13 06:33 PM

Quote:

That's why I wear gloves if I am interested in working at high magnifications, just touching the tube to track will cause a tube current.




That's one of the nice aspects to yesteryear's Cave-era tubed Newtonians... the "fiberglass" tubes they employed. My old 'Optical Craftsmen' 6" F8 is like that... not much thermal gets thru that stuff! Having an oversized tube of such material would be nice, as well- enabling the thermals inside to "chimney" up & out, hugging the walls, while still staying (mostly?) out of the light-path. Mine's tube is, unfortunately, *not* oversized in the least, but a rather tight fit to the optic. Still seems to work pretty well, tho.


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Re: truss vs solid tube dob new [Re: Mike B]
      #5840575 - 05/04/13 06:48 PM

Quote:

Quote:

That's why I wear gloves if I am interested in working at high magnifications, just touching the tube to track will cause a tube current.




That's one of the nice aspects to yesteryear's Cave-era tubed Newtonians... the "fiberglass" tubes they employed. My old 'Optical Craftsmen' 6" F8 is like that... not much thermal gets thru that stuff! Having an oversized tube of such material would be nice, as well- enabling the thermals inside to "chimney" up & out, hugging the walls, while still staying (mostly?) out of the light-path. Mine's tube is, unfortunately, *not* oversized in the least, but a rather tight fit to the optic. Still seems to work pretty well, tho.




That's one of the nice aspects. But those tubes, they are not light. I think the OTA on my 12.5 inch F/6 Meade weighs right around 100lbs, the whole rig is close to 300 lbs.

Jon


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Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5840588 - 05/04/13 07:00 PM

Really? Heavier than today's comparable metal tube? My 6" is small enough that it doesn't seem too weighty to me... and i don't have a contemporary metal-tubed 6" handy to compare.


Who else & what else are today's higher-end tubers coming mounted in?... besides "Sonotube". Carbon-fiber?


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Re: truss vs solid tube dob new [Re: paulr57]
      #5841326 - 05/05/13 09:23 AM

Now ya'll have overwhelmed me! In a good way though! Summer time in NC can be brutal at times and heat waves are everywhere. I just assumed it was the natural order of life especially when I fill my eyepiece with a full moon!

One thing I do as a matter of routine is I tend to wait til my target is very high in the sky so I don't have to fight some of the atmospheric waves I notice when viewing closer to the horizon.

I still consider myself a noob even though I got my first telescope 20 years ago! So please forgive me if I act like a wide eyed child in a candy store with a fistful of money!


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Re: truss vs solid tube dob new [Re: paulr57]
      #5841426 - 05/05/13 10:49 AM

I don't recall you stating what scope you had- but if it's a Dob, then in warm weather it'll help greatly if you set it up on grass for your viewing session- rather than pavement, which typically retains much heat, & re-radiates it long into the nite. This plays major havoc on a Dob's views, since its mirror is slung so low to the ground, and all that warm air!

Beyond that, use a fan to help speed the mirror's reaching ambient temps, and try to avoid viewing directly over heat-radiating pavement, rooftops, & vents.

Keeps the wide-eyed child happier in me, too!


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Re: truss vs solid tube dob new [Re: Mike B]
      #5841622 - 05/05/13 12:54 PM

Quote:

Really? Heavier than today's comparable metal tube? My 6" is small enough that it doesn't seem too weighty to me... and i don't have a contemporary metal-tubed 6" handy to compare.


Who else & what else are today's higher-end tubers coming mounted in?... besides "Sonotube". Carbon-fiber?




Those big old scopes used thick walled phenolic tubes. The tube is about 0.40" wall, 15 inches in diameter, 75 inches long. I calculate the tube itself weighs over 70 lbs. Add in a full thickness 12.5 inch pyrex mirror, the cell and the rotating ring assembly, it's at least 100 lbs. The counter weights weigh 85lbs.

Jon


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Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5841807 - 05/05/13 02:51 PM

My old Meade 826c "Red-tuber" Newt, 8" F6, had the phenolic tube... was feather light that i remember. For the 12-16" tubers must be what you're talking about- tho i can't recall ever seeing one up-close.

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Re: truss vs solid tube dob new [Re: Pinbout]
      #5841818 - 05/05/13 02:58 PM

Quote:

Quote:

have, however, seen heat rising from a group of people standing around and jawing about 10' in front of my scope, even though they weren't blocking the light.




that's cool but that would be expected if they were under the optical axis.

This typical discussion usually centers around the person hovering over the focuser and how their body heat/breath effects the air in the optical axis.




Danny,

Certainly this is in regard to the concern of the optical axis and perhaps several other factors on the pros and cons of tubes and trusses. I would like to reiterate though, that a person does not have to place their hand in or stand under a telescope just to disturb the images. People standing several feet away can still cause image degradation and what Don is talking about is very valid.

At Charlton Flats, the seeing can drop to .5 arc seconds and if a person is standing upwind, anywhere near the front or side of a telescope, observers will sometimes politely ask them to step somewhere else to remove doubt. It can make a difference and it certainly matters from world class observing platforms like Charlton, it's all relative. You can even see the pulsations of an airy disc from a telescopes stepper motors in some cases.

Take a match stick, light it and then blow it out. The remaining smoke may mix and disperse in several directions, or in one direction. An observer may not feel much of anything, but that does not mean the air carrying the thermals is standing still. Everything in the air from you and around the telescope is moving and that's all it can take to degrade a world class image.

The better the seeing location, the higher the expectation is by the observer who appreciates that difference. I didn't drive 60 miles to a semi light polluted sky like Charlton in search of darkness. I went in search of world class seeing and transparency to see things very few observers get to experience in a lifetime. A tube still has several other advantages as well, it isn't just this.

Human beings are a tremendous source of heat plumes, especially standing right next to the optical entrance of a telescope. If the average body temperate is 98 degrees F. and your ambient air temperature is 60 degrees F. that's an incredible difference.

A primary optic just 2 degrees F. above ambient can exhibit some boundary effects. By comparison, a human with a Delta T of 38 degrees F. is staggering and cannot be ignored. It's all about the Delta T. It is for this reason that professional observatories who give public tours require that all people be removed from the dome by a certain hour. Sensitive detectors can easily be disrupted.


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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5841913 - 05/05/13 03:53 PM

Quote:

I didn't drive 60 miles to a semi light polluted sky like Charlton in search of darkness. I went in search of world class seeing and transparency to see things very few observers get to experience in a lifetime.



Is there a particular spot/location where you and others setup their telescopes at Charlton Flats?


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Re: truss vs solid tube dob new [Re: paulr57]
      #5841970 - 05/05/13 04:21 PM

Teeter's tube dobs are felt lined, hope that helps with body heat issues. I've seen body heat plumes with my cats under very good conditions if my hand is by a gap in the dew shield and seem to recall something similar with my long long ago 6" F/8 newt with excellent optics. David

Edited by dscarpa (05/06/13 07:06 PM)


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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5842007 - 05/05/13 04:44 PM

Quote:

Human beings are a tremendous source of heat plumes, especially standing right next to the optical entrance of a telescope.




That's why I eat apples while I'm observing...if you get too close and mess up the air you better duck...

but seriously, the plumes don't mix very welln as seen in your previous links, and most of the heat comes off the top of the head, ~70%, away from the optical axis.

I didn't put my shroud on last night and saturn was low enough that while I was sitting my feet were under the open truss, I could see it was effecting the air, but I didn't bother to put the shroud on cause the seeing wasn't good enough to begin with. I still got nice colored belts on the disc and could see a b c rings, 5 moons. just couldn't push the mag as I usually would.



Edited by Pinbout (05/05/13 06:02 PM)


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Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5842008 - 05/05/13 04:46 PM

Daniel,

Yes, the deltaT is a huge difference, but the outside of the garments I'm wearing are not 98.6 degrees--they are considerably colder because they insulate my body from the cold. The only parts of my body giving off large amounts of heat, typically, are my hands and face, and they are too small in area to have much effect unless I hold a hand in the light path.

In your defense, however, when I had a steel-tubed 6" f/5, sitting with my legs under the scope caused heat plumes to appear in the star images.
Covering my legs with a blanket stopped the heat plumes.
I rebuilt the scope with a fiberglass tube and the sensitivity to placement of my legs or hands disappeared. These new tube liners, or even flocking the inside of the tube, stand a good chance of cutting down on this sensitivity, even with steel tubes.

Curiously, I don't notice any heat plumes from my body when I use a shroud on my dob, and ice or dew forms on the top side of the shroud. The shroud doesn't seem to hold heat or conduct it away from your hand. Part of that is the material, and part of it is the much greater clearance between the light path and the shroud, compared to a tubed scope. I wonder if shrouds made from space blanket material would be even better.


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cpr1
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Reged: 03/24/12

Loc: Louisiana
Re: truss vs solid tube dob new [Re: Starman1]
      #5842125 - 05/05/13 05:42 PM

Has anyone tried to sew in a mylar sheet or some type of similar insulation. Like the thin reflective stuff they use under metal roofs. It works really well to insulate roofs. At least that is what they put on metal shops around here.

It would have to be sew into the shroud somehow with a flat black backing.


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Jon Isaacs
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Reged: 06/16/04

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Re: truss vs solid tube dob new [Re: Achernar]
      #5842378 - 05/05/13 08:19 PM

Quote:

When you reach 15 or 16-inches, a truss is really the only practical option if you have to transport it. As for thermal issues, I don't see any disavantages at all, indeed my mirror cools off quite rapidly and I have an Obssession pattern mirror cell. I have a variable speed fan that I leave running all the time at low speed, without vibration problems and turning it off or on does not seem to affect the views. It's no worse or better than my 10-inch solid tube, also with a cooling fan.

Taras




So here's an honest question for you... Is your scope truly "rock solid" thermally stable? When the seeing is excellent, are you seeing nice clean, "refractor-like", in-focus, diffraction rings at say 800x?

Jon


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Daniel Mounsey
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Reged: 06/12/02

Re: truss vs solid tube dob new [Re: Starman1]
      #5842383 - 05/05/13 08:27 PM

Don,

Next time we observe, I'll bring a few tools to do some tests with your dob. I did try numerous experiments using insulated gloves, coats and what not, but the heat just kept pouring out, but that's not to say your points are not valid.


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Daniel Mounsey
Vendor (Woodland Hills)
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Reged: 06/12/02

Re: truss vs solid tube dob new [Re: Alph]
      #5842389 - 05/05/13 08:30 PM

Quote:

Quote:

I didn't drive 60 miles to a semi light polluted sky like Charlton in search of darkness. I went in search of world class seeing and transparency to see things very few observers get to experience in a lifetime.



Is there a particular spot/location where you and others setup their telescopes at Charlton Flats?




There is but it's currently closed for a while until political matters are solved with Angeles National Forest.


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Pinbout
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Reged: 02/22/10

Loc: nj
Re: truss vs solid tube dob new [Re: Daniel Mounsey]
      #5934504 - 06/22/13 12:04 PM

Hey Mr. Mounsey

check it out

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5933664/page...


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johnnyha
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Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: truss vs solid tube dob new [Re: Pinbout]
      #5934992 - 06/22/13 04:57 PM

My best thermal results have been blowing a 12" RV box fan, sitting on a chair, directly into the UTA of my almost-horizontal, shrouded 15" Classic Obsession down towards the mirror for cooldown... so cooling "from the top"... then while viewing having the box fan sitting on the chair opposite the scope from me at low speed, gently blowing my body heat directly away from the scope. I also have a three-speed brushless fan under the mirror that exhausts outwards that I sometimes keep on low speed while viewing.

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Achernar
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Reged: 02/25/06

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Re: truss vs solid tube dob new [Re: Jon Isaacs]
      #5935499 - 06/22/13 10:42 PM

I never have seen a night like that, that is where I would get a steady view at 800X. However, I can say that unless the temperature just keeps falling rapidly all night, I haven't noticed problems with tube currents in the 15-inch because it doesn't keep pace with temperature changes. I have a fully open tailgate and mirror cell with a cooling fan, and the cover on the rear of the mirror box is Ripstop with a large hole in it for air to flow through. The shroud is Ripstop also. I see a clear diffraction pattern on both sides of focus, one that shows mild over or under correction. In focus I have noted one faint diffraction ring around a star. The highest magnification I have used so far is 575X, the seeing where I live is just not good enough really to go much more than 400X. So yes, it appears to be quite thermally stable in that the telescope does keep pace with the temperature on most nights.

Taras


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