AstroMaster 130 Spidervane Modification

The spidervane modification has its roots in the results of the startests I performed on the scope. In the diffraction patterns the original 4-vane sipder produced very distinct diffractions.
This is of course partly due to the 4-vane configuration, which produces 4 strong diffraction spikes around bright stars. This is in some cases visually very pleasing and is some what expected of astrophotos. The original spidervanes also had an other issue which is visible in the startest image below.

The vanes produce a somewhat "blocky" star image most likely due to the 3mm thickness of the individual vanes. It is understandable that on a "budget" scope some compromises are made to lower the production costs.
An other issue I wanted to adress with the modification was to minimize the central obstruction size. In the original configuration the central obstruction is actually slightly more than the secondary mirror size requires. Secondly as I managed to chip the original secondary while trying to remove it from the mount, I purchased a slightly smaller secondary that still works on the scope without larger modifications to the tube . The original central obstruction is 44mm in diameter, which amounts to ~34% obstruction. The original secondary minor axis is 40mm. If mounted differently would already reduce the obstruction to ~31%. The new secondary has a minor axis of 37mm, which, if mounted correctly would give an obstruction of ~28%.  I'm hoping to get a little bit more contrast. Visually probably not notable, but when photographing though the scope then the situation might might be different.

I wanted to go for a rather simple design without any "gnarly" parts and easily upgradeable. Basically I want to be able to take the whole thing apart and make changes when necessary. The design basically consists of three parts; the central hub, detachable vanes and the secondary mount.
Unfortunately all the texts are in Finnish, but I think you get idea. As you can see I went for the 3-vane design in order to get rid of the 4 very bright diffraction spikes.
The main problem with the making of the vanes was to find thin and stiff enough material to do the job. It turned out that a metal ruler was more or less a perfect solution for it. Being only 1mm thick and very torsion and bending resistant, especially in the short lengths needed for this.
The central hub is made of POM (Polyoxymethylene) or simply a type of plastic which works well for precision parts and can handle temperatures down to -40C.  The secondary is mounted with three drops of standard silicone adhesive.

The final spider before painting matt black and installation of the secondary. As you can see the difference between the original and the modified vane is quite distinct. Of course the whole original plastic assembly needed to come off before the new vanes could be installed. The good thing is that the plastic tube end was attached to the tube with three screws with 120 degree separation, so no drilling was needed.
Below is the painted spider with the secondary installed (and the original for comparison) and the spider installed in to the scope.

Ever since the modification was completed the weather has been quite miserable, so no star tests have been performed with the new sipder installed. But when the skies clear and the temperatures rise to a manageable level I will perform the tests.


  1. hello,

    My name is Mitja and Im coming from Serbia. Im bought astromaster 130eq and i wish to do same modifications of spider vane. so i need some more informations about this. links or some plans how to do its ok. my idea its to get 3 vanes 1mm thickness. secondary will stay the same.

  2. Hi Mitja, I'll try to help you as much as I can. My suggestion is that you get rid of the original secondary holder. You can of course keep the mirror. You can contact me directly through my email mtoastro(enter the funny a here)

  3. How did you make the Central hub? Or Is is available for purchase

  4. Hi Bala, the central hub is my own design and manufacture. It's not available for purchase, but you can use the drawing on this page to make one. All you need is access to a lathe to make the hub and a steel ruler for the vanes. Some of the text is in Finnish but if you want I can provide a translation.