Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Reflectors

Pages: 1 | 2 | 3 | (show all)
Jeff Porter
super member
*****

Reged: 09/03/10

Loc: Utah
How much does your dob weigh per inch of aperture?
      #5769963 - 04/01/13 12:31 AM

Just curious to find out what some of the different dobs weigh per inch of aperture. Here is what I have...

17.5" StarStructure TL = 96 lbs. so
96 lbs/17.5" aperture = 5.5 lbs/inch of aperture

Orion XX12...
86.5 lbs./12" aperture = 7.2 lbs./inch of aperture.

Orion 6"
35 lbs./6 aperture = 5.8 lbs./inch of aperture.

I would love to hear from everyone from the Coulter owners to the ultralights.

Jeff P


Post Extras: Print Post   Remind Me!   Notify Moderator  
David Knisely
Postmaster
*****

Reged: 04/19/04

Loc: southeastern Nebraska
Re: How much does your dob weigh per inch of aperture? new [Re: Jeff Porter]
      #5770034 - 04/01/13 01:31 AM

My Orion XX14i weighs in at around 120 lbs, so that would be about 8.6 lbs per inch of aperture (and it is a heavy beast, although not quite as heavy as the XX14g). Clear skies to you.

Post Extras: Print Post   Remind Me!   Notify Moderator  
FirstSight
Duke of Deneb
*****

Reged: 12/26/05

Loc: Raleigh, NC
Re: How much does your dob weigh per inch of aperture? new [Re: David Knisely]
      #5770056 - 04/01/13 01:52 AM

80 lbs (base + OTA) / 12 inches aperture = 6.67 lbs/in.

Presumably, we don't count accessories such as finderscopes or Telrads or the removable wiring and batteries needed for e.g. dew heaters and fans; just the telescope structure itself.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed D
Carpal Tunnel
*****

Reged: 04/30/10

Loc: Sunny South Florida
Re: How much does your dob weigh per inch of aperture? new [Re: FirstSight]
      #5770181 - 04/01/13 05:51 AM

My 6" tube Dob weighs 30# fully loaded - 5# per inch

The 6" strut Dob should weigh 22# or less when finished - 3.7# per inch

Ed D


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: How much does your dob weigh per inch of aperture? new [Re: Jeff Porter]
      #5770219 - 04/01/13 07:26 AM

Quote:

Just curious to find out what some of the different dobs weigh per inch of aperture. Here is what I have...

17.5" StarStructure TL = 96 lbs. so
96 lbs/17.5" aperture = 5.5 lbs/inch of aperture

Orion XX12...
86.5 lbs./12" aperture = 7.2 lbs./inch of aperture.

Orion 6"
35 lbs./6 aperture = 5.8 lbs./inch of aperture.

I would love to hear from everyone from the Coulter owners to the ultralights.

Jeff P




In a scaled design, weight scales with the cube of the aperture. If everything is scaled up then a 12 inch Dob should weigh 8 times as much as a 6 inch. A small scope has a real advantage in a linear measure. One measure would be the ratio of the cube weight divided by the cube of the aperture. Some parts are not scaled, focusers... another measure might be pounds/square inch, the weight for a given amount of light gathering.

Note, in the interest of simplicity, the numbers below are in terms of "lb/inches squared", i.e. the aperture squared, this proportional to the area of the mirror.

Two examples:

- Jason Comet Hunter 480. This should pass muster and a Dob, it's on an alt-az mount. It's got a steel tube and metal mount. It's a 3 inch scope that weighs 4.75 lbs, it's weight to aperture ratio is 1.59 lbs/in, weight per square inch of mirror area is 0.53 lb/inch squared. Even with the 1.59 lb/in number, it could easily be much lighter. I have a 3 inch F/3.7 Newtonian OTA that weighs about 1.5 lbs, with a simple mount, it could be under 1 lb/inch.

This scope comes in at about one third the weight/aperture of the Star Structure but the Star Structure is clearly the lightweight design, the Comet 480 is not.



- 16 inch Dobstuff. This weighs about 90 lbs depending on the configuration, it's weight to aperture ratio is about 5.6 lbs/in. It's weight per square inch of mirror area is about 0.35 lbs per inch squared.

The mini-dob was not designed to be particularly light, steel tube, steel mounting, but at under 5 pounds, it really didn't need to be. On the other hand, the Dobstuff, needed to be light. The optics began their life as Meade Starfinder Dob, I believe that scope must have weighed about 150lbs, 9.4 lbs/in or 0.59 lbs/inch squared. It was basically unmanageable and something had to be done.

Looking at the scopes listed:

- 17.5 inch Star Structure: 0.313 lb/inch squared, 5.5 lb/in

- 12 inch Orion Dob: 0.601 lb/inch squared, 7.2 lb/in

- 6 inch Orion: 0.972 lb/inch squared, 5.8 lb/in

- 14 inch Orion Truss: 0.612 lb/inch squared, 8.6 lb/in

- 6 inch custom: 0.833 lb/inch squared, 5 lb/inc.

- 3 inch Jason: 0.59 lb/inch squared, 1.6 lb/in

- 16 inch Dobstuff: 0.35 lb/inch squared, 5.6 lb/in

If one is looking for a measure of the effectiveness of a lightweight design, I don't think the linear lb/in is reasonable. The 17.5 inch Star Structure at 90lbs is well executed design that goes a long way to minimizing the weight and yet the linear metric does not show that. To my mind, if the smaller scopes were built with such attention to detail, they could be considerably lighter, at 0.313 lb/inch squared, a 12 inch Dob would weight 45 lbs, not at all unreasonable and an even light scope could be built.

Looking the various weights/inch square, I think it does a better job as a metric for sorting out what is a lightweight design. However, the weight/inch cubed might be more appropriate, if one were comparing different animals, this would probably be the metric one uses. The Star Structure comes in at 0.018 lb/inch^3, at weight over inches cubed ratio, a 12 inch Dob would weigh 31 lbs, possible but really pushing the limit. But then, the Star Structure is really pushing the limit for a 17.5 inch scope, it's just that our expectations are skewed because of the simple practical fact that a large Dob has to be manageable. I don't know how much a 25 inch Obsession weighs, probably between 225 lbs and 250lbs. If a 25 inch Dob were built using the same technology used for a steel tube Dob, it would probably weigh at least 500 lbs.

Just some stuff to think about...

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
JimMo
I'd Rather Do It Myself


Reged: 01/08/07

Loc: Under the SE Michigan lightdom...
Re: How much does your dob weigh per inch of aperture? new [Re: Jon Isaacs]
      #5770244 - 04/01/13 08:06 AM

My 14.5" is a behemoth and I have no idea what it all weighs. I'm sure it's well over 100 lbs with a deep mirror box so lots of 3/4" plywood which is doubled for the altitude bearings. I've contemplated rebuilding it but it is easy to transport with the wheel barrel handles and holds collimation extremely well with no flex of the structure at all. In other words it's a tank. Let's say 120 lbs. which is 8.28 lbs. per inch.

Post Extras: Print Post   Remind Me!   Notify Moderator  
tezster
scholastic sledgehammer
*****

Reged: 07/14/09

Loc: Missisauga, Canada
Re: How much does your dob weigh per inch of aperture? new [Re: Jeff Porter]
      #5770248 - 04/01/13 08:14 AM Attachment (10 downloads)

My 10" DobStuff weighs around 40lbs., so 4lb/inch. I'd love to see some 'suitcase' scopes, Sumerian optics designs, and other home-made light-weight designs.

Edited by tezster (04/01/13 08:22 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
nicknacknock
professor emeritus
*****

Reged: 02/20/12

Loc: In a galaxy far far away...
Re: How much does your dob weigh per inch of aperture? new [Re: JimMo]
      #5770249 - 04/01/13 08:15 AM

3.7 per inch lightweight structure does have a few advantages...

Post Extras: Print Post   Remind Me!   Notify Moderator  
isawit
member


Reged: 01/22/13

Loc: Lake Phelps, North Carolina
Re: How much does your dob weigh per inch of aperture? new [Re: JimMo]
      #5770251 - 04/01/13 08:16 AM

Apertura AD12 12"/86.1 lbs. = 7.175 lb. per inch of aperture

Post Extras: Print Post   Remind Me!   Notify Moderator  
Mirzam
Post Laureate
*****

Reged: 04/01/08

Loc: Lovettsville, VA
Re: How much does your dob weigh per inch of aperture? new [Re: isawit]
      #5770257 - 04/01/13 08:22 AM Attachment (13 downloads)

68 lbs, 14" aperture homebuilt travel scope = 4.85 lb/in. It helps that the Mark Cowan quartz mirror only weighs 11 lbs.

JimC


Post Extras: Print Post   Remind Me!   Notify Moderator  
ctcables
professor emeritus


Reged: 11/14/06

Loc: Oregon
Re: How much does your dob weigh per inch of aperture? new [Re: Mirzam]
      #5770291 - 04/01/13 08:57 AM

32/14.5 is 2.2lbs can pick it up with one hand and go with no problem. Working on a 20" I hope to get in around 40lbs + 10lbs for the bace with drive. We will see how it turns out.



Edited by ctcables (04/02/13 12:10 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
nirvanix
Carpal Tunnel


Reged: 06/07/07

Loc: Saskatoon, SK
Re: How much does your dob weigh per inch of aperture? new [Re: ctcables]
      #5770430 - 04/01/13 10:14 AM

13.1" original Coulter weighs 150 lbs, so about 11.5 lbs per inch.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff Porter
super member
*****

Reged: 09/03/10

Loc: Utah
Re: How much does your dob weigh per inch of aperture? new [Re: Jon Isaacs]
      #5770467 - 04/01/13 10:35 AM

Jon,

Your points are well made. I didn't think to use either of the methods you mentioned but they do give a better representation of the differences between the various models. I really like the idea of weight/(aperture squared), so I will compile a list using that ratio from lightest to heaviest based on that criteria.

For everyone else, keep em coming.

Jeff P


Post Extras: Print Post   Remind Me!   Notify Moderator  
FirstSight
Duke of Deneb
*****

Reged: 12/26/05

Loc: Raleigh, NC
Re: How much does your dob weigh per inch of aperture? new [Re: Jeff Porter]
      #5770579 - 04/01/13 11:36 AM

Weight and bulk per inch of aperture is not purely advantageous (if relatively light) nor disadvantageous (if relatively heavy). For transportability, lower weight and bulk relative to aperture is an advantage, higher weight-to-aperture tends to be a disadvantage. For stability in breezy conditions or resistance to flexure, higher weight-to-aperture tends to be an advantage. A lighter-weight design can compensate by using stiffer, higher-quality materials, though usually this compensation comes at higher cost in materials and required quality of design and workmanship.

Winter Star Party (the site for which is directly on a wind-exposed south-facing beach berm) is an excellent test of the relative values of weight/bulk/materials/design/aperture/transportability. You can easily see who's thriving and who's not with what scopes on a temptingly clear, transparent night with just enough breeze to challenge the ability of scopes to provide stable views above about 150x, as well as getting a good idea what kind of vehicle capacity and human effort was necessary to transport them the distance from home to the site and set them up.

Edited by FirstSight (04/01/13 12:07 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Project Galileo
scholastic sledgehammer
*****

Reged: 11/14/07

Loc: Jefferson County, Colorado
Re: How much does your dob weigh per inch of aperture? new [Re: FirstSight]
      #5770682 - 04/01/13 12:12 PM

Loaded my modified LB16 weighs in at 120 lbs. That is 7.5 lbs per inch.

Post Extras: Print Post   Remind Me!   Notify Moderator  
BluewaterObserva
Postmaster
***

Reged: 05/18/04

Re: How much does your dob weigh per inch of aperture? new [Re: Project Galileo]
      #5770846 - 04/01/13 01:40 PM

Way to much.... Wood adds up quicker than I expoected.

Self-made 13.1" Truss dob.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tad S.
sage
*****

Reged: 08/28/06

Loc: SW Virginia
Re: How much does your dob weigh per inch of aperture? new [Re: BluewaterObserva]
      #5770928 - 04/01/13 02:23 PM

My modified XT8i now has a 200mm mirror and a few accessories that bump the weight to 42 lbs. That comes out to 5.27#/in.

Stock the XT8i is 41.6 lbs for a 203mm mirror (5.2#/in).

--Tad


Post Extras: Print Post   Remind Me!   Notify Moderator  
careysub
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: How much does your dob weigh per inch of aperture? new [Re: nirvanix]
      #5771566 - 04/01/13 07:47 PM

From a spreadsheet of compiled weights (mostly from a thread here about a year ago, I added the HO offerings and the Orion XX16g recently). Ordered from the lowest Lb/In^2 "figure of merit" to the highest"

---------------------Aperture-Wt. (lb)--Lb/In---Lb/In^2
Hubble Optics UL18------18------72------4.00-----0.22
Hubble Optics UL16------16------60------3.75-----0.23
Hubble Optics UL14------14------48------3.43-----0.24
Webster D18-------------18------92------5.11-----0.28
DobStuff 17.5 ----------17.5----89------5.09-----0.29
Obsession 20 UC---------20-----124------6.20-----0.31
Obsession 18 UC---------18-----105------5.83-----0.32
Obsession 15 UC---------15------79------5.27-----0.35
DobStuff 14-------------14------70------5.00-----0.36
Obsession 20 Classic----20-----147------7.35-----0.37
Obsession 18 Classic----18-----126------7.00-----0.39
Starmaster 20-----------20-----156------7.80-----0.39
StarStructure 15 TL-----15------88------5.87-----0.39
Obsession 15 Classic----15------89------5.93-----0.40
Obsession 12.5 Classic--12.5----65------5.20-----0.42
Starmaster 18-----------18-----138------7.67-----0.43
Starmaster 14.5---------14.5----96------6.62-----0.46
Starmaster 16-----------16-----121------7.56-----0.47
StarStructure 12.5 TL---12.5----78------6.24-----0.50
LightBridge 16----------16-----128------8.00-----0.50
Zhumell 12--------------12------75------6.25-----0.52
Zhumell 16--------------16-----134------8.38-----0.52
Orion XT10--------------10------53------5.30-----0.53
LightBridge 12----------12------80------6.67-----0.56
Zhumell 10--------------10------60------6.00-----0.60
Orion XX12--------------12------87------7.25-----0.60
Starmaster 11-----------11------74------6.73-----0.61
Orion XX14i-------------14-----120------8.57-----0.61
LightBridge 10----------10------65------6.50-----0.65
Orion XX16g-------------16-----195-----12.19-----0.76

Edited by careysub (04/01/13 09:04 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
buddyjesus
Carpal Tunnel
*****

Reged: 07/07/10

Loc: Davison, Michigan
Re: How much does your dob weigh per inch of aperture? new [Re: careysub]
      #5771587 - 04/01/13 07:55 PM

http://royalsociety.org/exhibitions/350years/newton-telescope/

would love to find out how much this one weighs personally.


Post Extras: Print Post   Remind Me!   Notify Moderator  
kfrederick
Carpal Tunnel


Reged: 02/01/08

Re: How much does your dob weigh per inch of aperture? new [Re: buddyjesus]
      #5771757 - 04/01/13 09:42 PM

The HST is weightless so it wins

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | (show all)


Extra information
23 registered and 26 anonymous users are browsing this forum.

Moderator:  ausastronomer, Phillip Creed, JayinUT, okieav8r 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 2059

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics