After a short testing of the GSO Imaging Newton 303/1212 mm OTA, I decided to retain only the optics and build an entirely new telescope from scratch. The original tube proved to be mechanically inadequate for serious astrophotography. The newly designed structure is a Serrurier Truss Newtonian, engineered to maximize mechanical rigidity, thermal stability, and performance under demanding imaging conditions.
Design Inspiration
This build was heavily inspired by Rolf Olsen’s custom Serrurier truss Newtonian telescope, a benchmark in DIY astrophotography telescopes. His attention to structural stability and imaging performance set the standard for what a Newtonian truss system can achieve when properly designed and executed.
Special thanks to Rolf Olsen for sharing his extensive documentation, design philosophy and kind support, which served as an essential source of inspiration throughout this project.
Flaws of the Original GSO Tube
- Severe flexure issues caused optical misalignment under load.
- Extremely sensitive to temperature changes, with internal turbulence and frequent focus shifts.
- Lightweight construction and materials were unfit to support imaging equipment reliably.
- The tube design prevented the optics from performing at their true potential.
Design & Build: Serrurier Truss Newtonian
The new structure is based on the Serrurier truss design: the secondary cage and primary mirror box are connected by symmetrically placed aluminum struts. This layout ensures that any flexure remains symmetrical and does not shift the focal plane.
Main Features:
- Secondary cage made from CNC-machined multi-layered poplar plywood, compact and lightweight, with custom 3D-printed aluminum pipe joints.
- Mirror cell from plywood, CNC-machined with 3-point flotation system and 3 lock knobs.
- 1.5 mm tickness 16 aluminum truss tubes.
- 4 mm tickness aluminium central box/brace
- GSO original spider to support the secondary mirror.
- GSO low-profile Crayford focuser, reused from the original tube.
GSO Optics
- Primary mirror: 303 mm f/4.
- Secondary mirror: 88mm.
Although the GSO optics are generally good, they were held back by the poor mechanical quality of the original OTA. The new Serrurier structure allows them to perform to their full capacity in demanding imaging setups.
Benefits of the New Structure
- Total mechanical rigidity: no flexure even with heavy cameras and accessories.
- Fast thermal equilibration: the open structure promotes air circulation and prevents turbulence.
- Precision-engineered: all components were designed in CAD and CNC-machined to tight tolerances.
Field Performance
- No focus drift or misalignment during long imaging sessions.
- Consistently sharp and stable images.
- Thermal performance significantly improved over the original tube.
Weight and Mount Compatibility
- Total weight of custom truss telescope: 19 kg
- Original GSO tube weight: 22 kg
A 3 kg reduction, with greatly improved balance and lower stress on the mount, resulting in better guiding performance.
Replacing the GSO OTA with a custom Serrurier Truss structure has completely transformed this telescope. The new build is lighter, stiffer, and purpose-built for astrophotography. The optics, once limited by the original tube, now operate in optimal conditions with no compromises. This project has proven that even mid-tier commercial optics can deliver outstanding results when supported by a well-designed mechanical structure.
