Jump to content


Small (150mm) open truss pros and cons

Recommended Posts

While still waiting for my mirror, I'm looking at materials to build the scope, especially the tube.

I'm starting to play around with the idea of an open truss since large enough PVC pipes are rarely available in lengths less than 6m and I'm really not fond of the idea of using a cardboard tube.

All of the normal considerations for building a truss is irrelevant at this size and I can think of a lot of cons. I do think it would look cool though, and I don't think I've ever seen such a small open truss scope.

Why would you encourage or discourage the construction of such a small open truss scope?

Link to post
Share on other sites

It can be frustrating not having suitable materials to make a conventional tube, a truss tube can certainly provide a workaround. I have a 6" truss tube Newtonian that I built as a rough plan prior to making a 30". There is quite a bit of work involved at any aperture but it does look cool. I won't try and add to the list of cons that you have identified but to be honest a wooden square tube for a 6" has a lot going for it on pros. Easy to make, cheap, available materials, the square section simplifies fitting components and also discourages the circulation of tube currents. I could go on.....   :icon_biggrin:

Link to post
Share on other sites


Someone here on SGL built this the post was a couple of years ago now. I fancy having a go at one if I even get a long focal length 150mm mirror, the 1200mm variety. I did ask if any plans existed but it was done somewhat by trial and error. Kept a few of the images.

It is/was a 6" but built as an ultra portable, not a kind of permanent truss.

Edited by ronin
  • Like 2
Link to post
Share on other sites

Thanks for all the replies. It's reassuring to know that I am not completely crazy. @ronin, that's a really awesome design in the picture, I have something similar in mind for the truss, but I don't think I'll go for the dobsonian mount. Next is to decide if I want to be able to disassemble it or keep it permanent. Permanent will be less work, but portable is novel:icon_biggrin:.

11 hours ago, Peter Drew said:

I won't try and add to the list of cons that you have identified but to be honest a wooden square tube for a 6" has a lot going for it on pros. Easy to make, cheap, available materials, the square section simplifies fitting components and also discourages the circulation of tube currents. I could go on.....   :icon_biggrin:

I've seen few wooden "tube" designs in in octagons and squares etc. and to be honest, I don't really like the look of it, but you're absolutely right, a square assembly will make a lot of tasks a walk in the park, like mounting the focuser and secondary mirror.

I am curious as to what effect an enclosure has on the view quality. People go through painstaking effort to blacken a tube's inside to get rid of stray light rays. With a truss you allow even more strays in, or is there something I don't completely understand?

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By Quetzalcoatl72
      I'm after a cassegrain reflector but I don't know which one to buy,
      I have a celestron c5 and it worked wonders for all fields, I now want the same but twice as powerful as my final upgrade
      I am looking at a c9.5 for £1350 or a c11 for £2000, My question is an extra 2.75" focal worth it for £750 more?
      I will likely purchase one this week
    • By Cosmic Geoff
      With reluctance I am looking to sell my 200mm aperture f5 Helios Newtonian OTA. (Helios is a brand that became incorporated into Skywatcher - this closely resembles Skywatcher OTAs)
      The Helios is offered with single speed rack & pinion focuser, tube rings, 22 to 1.25" adaptor, dovetail bar and grab handle for £90 o.n.o.  In good condition except that the dovetail bar appears to be discoloured by exposure to sunlight.
      I have not used the telescope for many months and with a persistent problem in my right arm my enthusiasm for moving heavy kit around has diminished.
      Buyer to collect from North Bucks.
      Offered as option with the OTA: EQ5 mount with RA drive + 6 volt sealed lead-acid battery +charger + standard and extra long Dec slow motion manual shafts. £150. Condition - used but working.
      If I sell the OTA I will be looking to dispose of its accessories:
      9x50 Skywatcher straight finder - in excellent condition except that the small plastic dust cap is missing.
      Cheshire collimator, boxed, as new.
      Helical fine focuser, range 10mm, ID 1.25", screws into 2"adapter.
      3x Datysun Barlow, as new, boxed.
      Widefield eyepiece, 22mm f.l., 30mm body (note not 1.25")  with built in focus, works well with this telescope.
      Plastic collimation cap (no cost).
      This bundle would cost around £114 new - offered if bought with scope at £75 o.n.o.

    • By 25585
      Like many I think Telrads are great scope sites. And want to use mine with different scopes. But I don't want to stick a base to a nice looking OTA.
      All base types seem to be curved so sticking to a flat surface such as an accessory plate is not possible.
      The only option seems to be using two holes in its base, if they line up with those on a plate. Are there any ideas out there, or aftermarket Telrad bases apart from the company ones?
    • By bottletopburly
      Decided to put  cooling fans on my newtonians a 200pds and a 130pds ,used a 120mm on the 200 and a 80mm on the 130pds ,i used, Be Quite silent Wings2 fans they  use rifle bearings and are so quite German made, i did the 200 first and was impressed with this make so ordered the same make for the 130 pds it comes with a lead with four wires but only needed neg ang pos so snipped other two out ,  made a disc from plastic and cut out around collimation screws on primary then used velcro to attach to OTA  fitted a 2.1mm  dc socket on to the disc then bought a usb lead  to 2.1mm barrel though i may fit another 2.1mm socket on my power box and use 12v either way it works ,i used a dimmer on the 200pds but it doesnt need it and wouldn't use it again but its fitted now so will leave in place. 

    • By Ulysses31
      So, I have gone and got myself a Skywatcher Star Discovery 150p, which has so far proved to be a very good little scope and I've had some very good results.
      I have now got the bug for imaging and have gone out and got myself a second hand Nikon D5100 and verious other equipment needed to do this, only to now find I can't get Prime Focus!!!!!!!! So the only way I can image is using a barlow x2 which obviously changes the F ratio from F5.5 to F11 slowing everything x2 this isn't to bad for planetary imaging but for DSO images not so good!!! 
      After searching through lots of videos on to do this all I can find is...... 
      I can either butcher the standard rack and pinion focuser that's fitted on it by cutting it down and rethreading it or by moving the primary up by 20-25mm,  which seems a shame to do a brand new scope still under warranty! 
      The only other option I have come up with is changing the focuser to a Skywatcher Low Profile  Dual Speed Focuser For Newtonian Reflectors. 
      Could anyone out there shed any light on this before I spend another £130 on the new focuser. 
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.