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Collapsible or Solid Tube


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Hi all,

I would like to ask about the advantages and disadvantages of a collapsible dobsonian telescope. Here is two dobs, Sky-Watcher Traditional Dobsonian 10″ and Sky-Watcher Collapsible Dobsonian 10″, should I get the first one or the second one for visual observing(10inch dob is good for VO, just want to ask which one is a better choice).

Clear Skies

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As an owner of a collapsible 8" Skywatcher Dob.  With all its advantages, if I bought again I certainly wouldn't even consider a solid bodied telescope.  Mine holds it's collimation with no issues - only been collimated once when I got it and been lugged about several times since with no issues.  I find no stray light issues at night - for daytime sun use I add a home-made cover to the trusses.  Storage is certainly the issue where it wins against a solid tube hands-down and I do believe it would have to be far easier to move around that it's solid bodied equivalent.

I could perhaps see a solid bodied one in an observatory where it doesn't need to be moved from, but if you want to store it in a house or shed then do yourself a favour and get a collapsible one.

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I wouldn't think of either type as better, it's more a case looking at their relative merits and picking the type that is better suited to your preferences.

Some of the advantages of a truss are they can be broken down into smaller and lighter pieces for storage, carrying, and transport, they cool down quicker, the mirrors are easier to access if you need to clean them or fiddle with them, they don't catch the wind so much, they don't need so much flocking if you prefer flocked innards.

Some of the advantages of a solid tube are greater rigidity for holding collimation and attaching heavier accessories, natural protection against dew, stray light, animals/insects/leaves/dust etc, faster to set up and take down because... no truss rods to put together, you can attach and set up finders, heaters, eyepieces etc so they are pre set and leave them like that, and collimation is less likely to be needed in the field, cheaper, lighter overall, simpler so less to go wrong.

I would recommend doing checks as to the spaces you could store and transport the telescope in, and check the weight/bulk that you can carry. If you can store it and carry it I would go for a solid tube.

Where a truss really pulls ahead is that it can make it possible to get a bigger aperture that can still be stored, transported, and set up, which could make the trade offs worthwhile depending on what you are looking for.

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10" is right at the cusp of where being collapsible or a truss design starts to make sense from a storage and transport perspective.  At 8" or less, it makes much less of a difference.  I would never consider anything but a truss for 12" and up.  At 15" and up, you've really got to start looking at the weight of the individual components to make sure you can heft them around.  My 15" mirror box at 65 pounds is at the limit of what I can lift.  A solid, 2" thick mirror is quite heavy when encased in 3/4" oak.  The biggest and best truss scopes come with removeable mirror boxes and sometimes tapered or honeycomb mirrors to reduce the weight of each component or to improve cooling.  Eventually, you need wheelbarrow handles and pneumatic tires to move the biggest Dobs around.

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The flextubes are slightly heavier than the solid tubes oddly enough. If you need a tube that will get shorter for transport / strorage then the flextube is the way to go but you will need to invest in a light shroud.

Optically they are both the same.

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4 hours ago, Paz said:

faster to set up and take down because... no truss rods to put together,

"No truss rods to put together" is a bit misleading.  On my 8" Dob the truss rods are in situ.  You just loosen three nuts and literally pull the top up into the air until it stops and then tighten the hand-driven nuts backup - 10 seconds tops and as quick to reverse!  I know some of the really big truss rod OTA's are a bit more like a Meccano set, but the Skywatcher flex-tubes are simplicity itself to extend and use and then collapse.

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24 minutes ago, JOC said:

"No truss rods to put together" is a bit misleading.  On my 8" Dob the truss rods are in situ.  You just loosen three nuts and literally pull the top up into the air until it stops and then tighten the hand-driven nuts backup - 10 seconds tops and as quick to reverse!  I know some of the really big truss rod OTA's are a bit more like a Meccano set, but the Skywatcher flex-tubes are simplicity itself to extend and use and then collapse.

You are right, I should have explained this.

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Its a bit of a wash if you ask me.

Both work. Personally I see little point in truss scopes under 12" unless one is looking at a high portability suitcase variety (the flex tube is certainly not this)  

For me the "flex" idea is a bit of a gimmick TBH as the stored version takes up exactly the same amount of floor space as the solid tube version.

IOW what's the point, if you are storing it under a shelf/table, get the flexttube, otherwise just get the solid tube and save yourself some money :) 

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If you want to view DSOs and your back garden is light polluted, a flex tube is the way to go. It gets the max aperture to a dark sky site and a dark sky is worth more than any filter and, IMHO, is the equivalent of 2” additional aperture to your viewing pleasure. 

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8 hours ago, John said:

The flextubes are slightly heavier than the solid tubes oddly enough. If you need a tube that will get shorter for transport / strorage then the flextube is the way to go but you will need to invest in a light shroud.

Optically they are both the same.

Ive read this before that truss tubes are slightly heavier. I still cant figure it out how its possible. Solid tube and truss may both have the same footprint, but truss scopes dont need as much head room. They can be stored in smaller spaces. 

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We have a 150 Skyliner and I recently bought a Heritage-130p Flextube just for myself. The reason being I have a narrow back hall, then back garden steps to navigate and although the 150 isn't too heavy, it is awkward and I need my OH to help me take it out. The Flextube I can pick up unaided as it is so neat and light and I prefer that independence. Now I know you are looking at something a lot bigger, but these are the factors you need to consider.

If it's going in an observatory/garage or a quick flat wheel outside then a fixed tube is great. If it's not straightforward access, build yourself a mock up box of what it's like to cart around then make your decision off that IMO.

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1 hour ago, LukeSkywatcher said:

Ive read this before that truss tubes are slightly heavier. I still cant figure it out how its possible. Solid tube and truss may both have the same footprint, but truss scopes dont need as much head room. They can be stored in smaller spaces. 

Having used both the solid tube and a flextube 12" Skywatcher dobs the flextube is slightly heavier I can assure you Paul.

Both were fine scopes though :smiley:

 

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36 minutes ago, John said:

Having used both the solid tube and a flextube 12" Skywatcher dobs the flextube is slightly heavier I can assure you Paul.

Both were fine scopes though :smiley:

 

I dont doubt you. How much heavier would you guess?.

Im assuming it down to materials used in construction.

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Have a 10" Flex tube

Easy to transport as do displays with schools and space badge scout/guide movement in Australia

Takes about 5 minutes to set up

Have a right angle spotting scope

I also cheat

Lay a laser pointer along dovetail of spotting scope, to give rough estimate where I want to view, and then find tune using spotting scope

Regulations lot stricter in Australia with respect to use of laser pointer, and only persons allowed to have are members of a incorporated astronomy society, for public displays

 

 

 

Skywatcher 10 inch Dobson.jpg

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I've a solid tube 250px, and it holds collimation ridiculously well!

For me, storage is dominated by the sizeable footprint: the tube length reduction with a flex tube offers no practical advantage for storage.

The two areas where I see the flex-tube having an advantage:

1. Transport in a car: flex tube shines here!

2. The ability to reduce the tube length to support binoviewing without incurring a magnifying glass path corrector (GPC).

Regarding #2, I do use a binoviewer on solar system targets with my 250px, and I have a 2.6x GPC. What it means is that I am restricted if I want lower magnifications, but here's the thing: I want 200x or so on planets, so this isn't really a significant issue.  I prefer mono on DSOs anyway.

The solid tube is slightly less hassle set up - less fuss sliding up/down, no fitting a light shroud, no moving parts/clamps to break with time, nothing to get stuck/jambed in place, secondary less likely to dew up.

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1 hour ago, niallk said:

less fuss sliding up/down

The slide is as smooth as silk - niallk, I sense there is a chance that you haven't played with one of these - for your own interest if you get a chance I think you would find it interesting to experiment with one

1 hour ago, niallk said:

no fitting a light shroud

Only strictly necessary during the day

1 hour ago, niallk said:

no moving parts/clamps to break with time, nothing to get stuck/jambed in place,

I look at how mine is put together and it seems pretty indestructible to me - I wouldn't mind betting there are folks with older ones than mine who are having no mechanical issues

1 hour ago, niallk said:

secondary less likely to dew up

I am not sure about this as the secondary faces the same direction as on the fixed tube and is the same distance from the end of the OTA.  I actually have dew shields, but I've not needed to fit them.

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While we're on this topic, how are the altitude motions on these flextubes versus truss Dobs with large trunnions?  The flextubes seem to ride on a small pivot point.  Does this mean they are more sensitive to imbalance when switching eyepieces?

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6 hours ago, JOC said:

Light shroud:

Only strictly necessary during the day

 

 

Not here - when I had a truss tube dob the shroud made a real difference to contrast on deep sky objects. The scope would have been quite ineffective on such targets without one. From a very dark sky site it's not as essential but keeping body heat and dust out of the optical path is still a good idea :smiley:

 

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