Tertiary and quaternary mirrors
Tertiary mirror, 8.3-m, aspherization comparable to that of a VLT-M1, radius of curvature ~ 2 x VLT-M1. Suitable blank probably available.
Very high aspherization of quaternary calls for novel fabrication & control approach
- 5.7-m, 27-mm thick Zerodur or Astro-Sital blank.
- 350 support points on 9 rings; aspherization generated by max. 6000 N force, within acceptable stress limits
- relatively high frequency residual ~ 12 ?m RMS, to be polished out.
- 2 suitable optical test set-up already identified.