10" - 12" Dobs - Solid Tube Or Flextube Types?

[Ian McCallum]

I'm still contemplating getting a larger Dob than I have at present.  I would like to move up from the Sky-Watcher 200P to something like either a 10" or 12", depending what I can get through my front door (unassembled).

What I'd like to know is, what's the current thinking on solid tube vs. collapsible tube?  I think the likes of weight/cool down time/light pollution ingress, etc.  What are the pros and cons between the two types?

Thoughts and ideas are most welcome, especially if I'm going to spend a lot of money on one.

[Dave scutt]

Hi Ian. 

I think if your taking it in and out of the house through the front door maybe a collapsible might be better unless you have a trolley or ramps 12" solid tube is heavy.

As for cool down maybe a fan will help mine is left in the shed leaving the fan running for a couple of hours, can't help with light pollution I have none

[Ian McCallum]

2 minutes ago, Dave scutt said:

Hi Ian. 

I think if your taking it in and out of the house through the front door maybe a collapsible might be better unless you have a trolley or ramps 12" solid tube is heavy.

As for cool down maybe a fan will help mine is left in the shed leaving the fan running for a couple of hours, can't help with light pollution I have none

If I got the flextube or truss type, then a shroud would be a must - I would get some light spillage from the sides, due to the neighbour's lights, etc.

[Carbon Brush]

Until a few months ago, I owned an SW250 flextube. It gave good views and was reasonably portable.
By portable I mean carrying the tube and rocker box separately. I did not record the weights.
It did not feel (muscles/back) a big step up from a 200P type of scope on an EQ mount.
Collimation was never a problem as the tubes always extend to the same position.
Having the flextube made transport, storage and handling easier.
As this scope had motor drives, balance was not a problem.
I did find that a bit of dismantling and adjustment on both motor drives helped deal with backlash and got a clutch release force that I liked.

Yesterday I collected the latest addition to my toybox. A 12" rigid tube dob. Basic (chipboard type) rocker box, no motor drives.
This felt like a BIG jump from the SW250. At around 1.5M long it meant removing the back seats for transport.
The base is approximately 650mm diameter. I think the 250 was around 550mm diameter. It doesn't sound much, but it feels big.
It is definitely a beast to handle. The rocker box comes in at about 14Kg and the tube with finder about 21Kg.
It is not just the tube weight, it is the size. A 'bear hug' carry is OK for a 200, or 250 but for a 300 you wonder if you know any friendly gibbons.
Yes the tube definitely benefits from handles of some sort. Mine has luggage strap types that may or may not be kept.

The undriven mount has definitely highlighted the need for good balance when you have smooth bearings. I used to rely on the motors holding the 250. But the 300 just tilts.
Without a finder it is balanced, add the finder and it falls.
I am still thinking about balancing techniques and have seen a few ideas.
At present I'm thinking in terms of a weight on the mirror cell opposite side to the focusser.
If I come up with a really good idea, I will post it😏
The alternative is brake with release lever, which may be easier to implement.

Most (affordable) newts benefit from some flocking to help with light pollution. By this I mean off axis light relecting around the tube..
If you put a dim red torch just catching the (supposedly very) black paint at the top, your view turns red.
With flocking this is much improved.

I can't comment on cool down as I have always stored scopes in unheated places.

HTH, David.

 

[HiveIndustries]

I just picked up a used Lightbridge 12" and I find myself repeatedly saying, "This is the smallest dob I'd ever have as a truss." I drive a Chevy Bolt (Opel Ampera in your parts) and a Hyundai Kona, both small bordering on tiny cars (for an American, anyways). I think a 10" tube would probably fit in my car just fine with the seat belt securing it good. The weight obviously matters but for me, I'm finding breaking down the structure to move 5 feet because I have 5 degrees of exposure of my target in between trees really subtracts from the usability, so much so that I'll be tinkering some kind of chassis and wheel system for it. If I had a 10" tube dob I'm confident I'd be able to avoid that without too many back issues.

All of this being said after the longest war of attrition with the clouds ever in the history of earth I finally saw the Orion Nebula this AM at around 6 right before the sun poked out of the horizon and it was still a really really faint affair in my Bortle 8 sky so I'm in the end very happy to have the bigger scope.

All of the above being considered, I'm happy with a large truss dob, personally and would probably still be happy from a size standpoint with a 14-16"

[Mr Spock]

The good thing about my 250mm flextube is how easily I can pick it up. I used to have a solid tube 250mm and had to sell it because I couldn't pick it up at all (bad back).

[Ian McCallum]

1 minute ago, Mr Spock said:

The good thing about my 250mm flextube is how easily I can pick it up. I used to have a solid tube 250mm and had to sell it because I couldn't pick it up at all (bad back).

It's good to read about someone else's experience with both models. 👍

[Dave scutt]

I had no problem with the dob being ballanced if the handles aren't to loose a good idea is too put some foam in between the tube and box . A good trolley and ramp would help moving in and out where stored 

[HiveIndustries]

2 minutes ago, Dave scutt said:

I had no problem with the dob being ballanced if the handles aren't to loose a good idea is too put some foam in between the tube and box . A good trolley and ramp would help moving in and out where stored 

Sorry to potentially derail but I gotta ask about your wheels. Is that a manufactured thing or did you fabricate it? If the former, got a link and how do you like it?

[Dave scutt]

It was custom made when I brought the dob,it's very easy to move around stable and no vibrations

[Beulah]

I have both solid tube and flex tube versions of the Skywatcher 300p and the flex tube does win a little,  as the tube can be partially extended for binoviewers (which I am planning to buy one day) and compactness during storage. The solid tube is much better at holding collimation...

Weight-wise,  the flex tube is a little heavier...

[Bigwings]

I have a Bresser 10" Dob which is solid tube. It's party trick is that it comes with tube rings on which it mounts big alt bearings when in Dob mode. Take these off and you can mount it as a conventional Newt. Mine sits on an AZ EQ6 mount in Alt Az mode. 

Just a thought but you may one day want a mount that will do everything including AP. 

Clear Skies

[John]

On 17/10/2021 at 13:01, HiveIndustries said:

... I'm finding breaking down the structure to move 5 feet because I have 5 degrees of exposure of my target in between trees really subtracts from the usability, so much so that I'll be tinkering some kind of chassis and wheel system for it.....

 

That was exactly the same experience that I had with my Meade Lightbridge 12 inch. In the end I decided to downsize to a 10 inch newtonian on an alt-azimuth mount and then later upsized again when a lighter weight UK made 12 inch optical tube came my way, for which I had a nice dobsonian mount built.

There is no doubt that the chinese made 12 inch dobsonians are good value but they are just the wrong side of the weight limit in my view, unless you get / make some sort of trolley system for them.

 

[Orange Smartie]

I have a StellaLyra 10" solid tube, which I bought to complement my Heritage 150p. 

I live in an 1850s house and the ceilings and doors are quite low - I would struggle to move anything larger through the house. As it is I have to:

Remove OTA from stand and place on the sofa.

Take dob base (14kg) outside and place at observing spot.

Return for OTA (about 16kg) and negotiate low ceilings, double doors, several steps, overhanging trees and an uneven lawn, before I can put it on its base.

10" is definitely manageable, even as with this week, when I knew I only had a brief window of opportunity.  12" would be too big for me unless I could store it outside.  I have no experience of the collapsible ones, but I do understand that they would be heavier.  I thought about an 8", but decided that if the optical performance was not sufficiently better than the 150p, I might become lazy about getting it out. As it is, the 10" is so obviously superior to the 6" that I don't mind the extra effort, but I think I would probably not put up with so much faff for a small improvement. 

In terms of balance, note that the StellaLyra has an adjustable pivot point (not really adjustable in use) so you can balance it against the majority of your eyepieces. 

Edited October 19, 2021 by Orange Smartie