A simple secondary mirror holder for a diagonal mirror with a minor axis of 4 cm or more.
I designed this secondary mirror holder for my dobson telescope building project using a 203 mm diameter primary mirror and a secondary mirror with 70 mm of minor axis.
This simple diagonal mirror holder has the basic 3 screws at 120 degrees to tune the tilt of the secondary mirror. Rotation and translation back and forward the telescope tube is achieved thanks to the knob in which an M4 nut is housed.
It is a simple but efficient design.

The photos show the printed holder painted with a flat black paint which looks nicer that way.
Additional is also the base part designed for M5 spider vanes for those who prefer a more robust spider vane even if it is not that necessary.

Parts needed

• 3 x cap head screws M3x45mm
• 3 x nuts M3
• 1 x pan head screw M4x65mm
• 1 x flat washer M4
• 3 x nuts M4
• 1 x wing nut M4 or normal M4 nut
• 1 spring
• Threaded rod M4 (for the spider vane)