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Collapsible or Solid Tube


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50 minutes ago, John said:

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:

 

Totally agree with John on this :) 

It also prevents stray objects from falling out of ones pockets and onto ones prime mirror :eek: 

54 minutes ago, Louis D said:

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?

There is little comparison between a SW flex tube and a scope with larger trunnions 

Eg I can swap from a huge 31mm 2" Nagler to a tiny 1.25" plossl and not need to adjust any counterweights or the balance set up of my scope in any way. 

Edit; guess I should explain......I have a scope with large trunnions ;) 

 

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6 minutes ago, swamp thing said:

It also prevents stray objects from falling out of ones pockets and onto ones prime mirror :eek: 

Somehow, I've managed to avoid this calamity :-D

OK, so I'll concede - it sounds like a shroud or not at night may depend on your local situation.

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2 hours ago, Louis D said:

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?

I have the Skywatcher Skyliner 10" flextube version with built-in Synscan system. The tube trunnions are several inches in diameter. The driven side slots into a large slotted wheel, and the passive side rests on 2 substantial rollers.

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I've only recently purchased a 10" Flextube GOTO scope and one advantage of this design that hasn't been mentioned (I don't think) is that the length of the tube has two "fixed" positions. One all the way out for visual and the other a bit shorter for imaging. It saves having to move the primary mirror up the tube to obtain focus. I haven't tried any imaging with it yet and it may not be an issue, but I have heard stories of people having to move their mirror up the tube.

Even at a dark site I would use a shroud even if only to prevent accidental dropping of items onto the main mirror.

Dave

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11 hours ago, JOC said:

The slide is as smooth as silk - niallk, I sense there is a chance that you haven't played with one of these 

Hi JOC, you are spot on correct: I haven't used a flex tube 1st hand.

When I was looking at getting a ~16", I was initially considering a 400p flex tube. I read loads of reviews, and watched some YouTube vids which were the basis for some of my potential reservations.

Please don't get me wrong - I think the SW scopes are great: overwhelmingly positive reviews, and I heartily recommend my 250px solid tube.

Cheers,

-Niall

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The only thing wrong with the Flextube is that name - it's really the last thing you should call an alternative newtonian tube system; you really don't want it to flex ! :rolleyes2:

The truss tube is a much more sensible term. As we all know, astronomers who have tried to lift a 16" solid tube newt often wear a truss for a while afterwards :grin:

 

 

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Dropping items onto the main mirror!

I must admit I hadn't even considered the chance of doing this.  In fact I would have thought that the truss tubes would have minimised this possiblity, i.e. if you dropped something through the middle gap that there would be a good chance of it falling through onto the floor and if you dropped something at the secondary vanes end I would have thought there was a good chance that it would fall out of the side before it hit the primary - something that couldn't happen with a solid tube.  In fact I would think you'd need to have the OTA fairly vertical before something falling at any point on a truss tube setup would be likely to hit the primary.

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43 minutes ago, JOC said:

Dropping items onto the main mirror!

I must admit I hadn't even considered the chance of doing this.  In fact I would have thought that the truss tubes would have minimised this possiblity, i.e. if you dropped something through the middle gap that there would be a good chance of it falling through onto the floor and if you dropped something at the secondary vanes end I would have thought there was a good chance that it would fall out of the side before it hit the primary - something that couldn't happen with a solid tube.  In fact I would think you'd need to have the OTA fairly vertical before something falling at any point on a truss tube setup would be likely to hit the primary.

Keeping light and body heat out of the optical path were the reasons that I used one and the light shroud made a really noticable difference to the first all the time and the second during the winter months. If you look for photos of truss tubed dobs in use at night (not the stock photos) you will see that many have shrouds fitted and there is good reason for that.

Other than the split tube and 3 sliding rods holding the two sections apart we are talking about exactly the same scope in this thread though. Your choice is good as is that of the owner of a solid tube version :icon_biggrin:

At the 10" size the difference in price is plus £100 for the Flextube (non-GOTO) version so "you takes your money and makes your choice". A lot of scope and performance for the £'s spent either way.

 

 

 

 

 

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I don't think anybody said it.. the truss type seems to be the winner among the forum users.. but here is my alternative vision:

This bellow is a very good looking telescope, old style, white solid tube. :icon_biggrin: I like how they look.

gY6EeB0.png

Solid tube!

6dPOtr1.jpg

 

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18 minutes ago, N3ptune said:

I don't think anybody said it.. the truss type seems to be the winner among the forum users.. but here is my alternative vision:

This bellow is a very good looking telescope, old style, white solid tube. :icon_biggrin: I like how they look.

gY6EeB0.png

Solid tube!

6dPOtr1.jpg

 

Have you ever tried to wrestle a 16" or larger solid tube Dob out of a full sized van?  I helped unload and setup a solid tube, vintage 17.5" Coulter some years back.  It filled the entire cargo length of a 12 passenger, full size van, weighed well over 100 pounds, required two people to move, and was still unwieldy.  No thank you.  You can keep your giant, solid tube Dob.

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On 12 December 2017 at 12:41, PeterCPC said:

I found that the flexi tube I had did not hold collimation. Go with the solid.

Peter

This. For 10 inch or less solid tube F5 or larger is usually OK for handling & exact collimation less critical. 

A 10 inch solid tube will fit front-to-back in a small hatchback car, my Austin Metro accomodates my Bresser 10 inch dob easily. 

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On 12 December 2017 at 16:27, Geoff Lister said:

My 10" Flextube holds collimation fairly well, takes a few seconds to extend, and fits in a cupboard that would not have enough height for a solid tube equivalent.

Flextubes are I guess the ideal compromise, part solid, part truss. It would be my choice for 14 inch+ primary mirror, a 12 solid OTA being at the limit for handling weight & width. 

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2 hours ago, 25585 said:

A 10 inch solid tube will fit front-to-back in a small hatchback car, my Austin Metro accomodates my Bresser 10 inch dob easily.

The 10" flextube OTA would, just about, fit in the passenger seat of my Mazda MX5 roadster/open-top-observatory, but there is no way I could fit the base in the boot.

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1 hour ago, Geoff Lister said:

The 10" flextube OTA would, just about, fit in the passenger seat of my Mazda MX5 roadster/open-top-observatory, but there is no way I could fit the base in the boot.

If the base is easy to disassemble & re-assemble that could be one solution perhaps?

I carry the OTA in my car & have a tow bar & small camping aluminium trailer which the base can go in. 

Even all-scaffold scopes have largish platforms and mirror boxes. 

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14 hours ago, Geoff Lister said:

The 10" flextube OTA would, just about, fit in the passenger seat of my Mazda MX5 roadster/open-top-observatory, but there is no way I could fit the base in the boot.

You 'need' to get yourself an Obsession 22" UC - well it fits in a Corvette!! ;)

John-Nymark-Corvette-th.jpg.f442591a418c922378218c1813cea027.jpg

(Taken from Obsession Telescope' s website)

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You guys all need Skoda Octavia Estates!  There are very few practical objects that cannot be fitted in back if an Octavia estate!  I once had an in-tact dining table and 6 chairs in one and, if memory serves , another time we managed 3 bicycles without needing ro remove their front whèels!

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I have a 12" truss type myself. If it were a solid OTA, I'd never take it anywhere. Since I'm able to break it down, I can actually fit the lower tube and base in the back seat of my 4-door car and everything else in the trunk and still be able to take my wife and daughter. If it were a solid OTA, I'd need a truck or SUV or have to leave my family behind if I wanted to take it anywhere. The downside is, I have more bags and pieces I have to haul around instead of just one tube. It does make it more manageable though as the individual pieces are lighter than a solid tube.

The real disadvantage for me is having to recolimate it every time I put it together. When you take something apart, it doesn't always go back together exactly the same way. If something is even 1mm off, over the length of the tube it can be VERY off. I would imagine a solid tube has less colimation issues. Colimation isn't difficult, it's just one more thing I need to worry about during setup though. Solid OTA's are also easier to setup in general. I also have to put four trusses on every time I put mine together. That's 12 more knobs I have to tighten and spend a couple extra minutes on and a secondary tube assembly I have to try and attach without dropping it.

Dew was mentioned. It was a problem the first time I was out on a night and the temperature dropped below the dew point. Now I have heaters on everything and don't worry about it.

There are pros and cons to each type, but optically and performancewise they are going to be extremely identical.

 

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I'm quite happy with my 300p Flextube Syncscan. Needs  collimation only when moved on its trolley, not when collapsed and left covered and parked in situ. A light shroud is needed but easily and cheaply made out of black yoga Matt.

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36 minutes ago, Buzzard75 said:

 

The real disadvantage for me is having to recolimate it every time I put it together. When you take something apart, it doesn't always go back together exactly the same way. If something is even 1mm off, over the length of the tube it can be VERY off. I would imagine a solid tube has less colimation issues. Colimation isn't difficult, it's just one more thing I need to worry about during setup though. Solid OTA's are also easier to setup in general. I also have to put four trusses on every time I put mine together. That's 12 more knobs I have to tighten and spend a couple extra minutes on and a secondary tube assembly I have to try and attach without dropping it.

Dew was mentioned. It was a problem the first time I was out on a night and the temperature dropped below the dew point. Now I have heaters on everything and don't worry about it.

There are pros and cons to each type, but optically and performancewise they are going to be extremely identical.

 

TBH buddy, any newt of 12" and over is going to need collimating every time you move it, be it a solid tube or a truss scope. It's to do with the mirrors weight. ;) 

 

 

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31 minutes ago, swamp thing said:

TBH buddy, any newt of 12" and over is going to need collimating every time you move it, be it a solid tube or a truss scope. It's to do with the mirrors weight. ;) 

 

 

I was referring more to the secondary and having to take apart the trusses, but yeah, the primary almost always needs to be slightly adjusted as well.

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