![Truss tube](https://image.jimcdn.com/app/cms/image/transf/dimension=300x1024:format=jpg/path/sd346316ed6df6d14/image/if9d0862514a0b6fb/version/1403529166/truss-tube.jpg)
Primary mirror cage
The assembly of the optical tube is progressing well.
The primary mirror cage is the most massive part of the optical tube assembly. It is a truss-tube made of powder lacquered square bar steel. To minimize the mass during assembly, the focus tube, back plate and primary baffle tube were removed.