4MOST - 4-metre Multi-Object Spectroscopic Telescope
4-m Multi-Object Spectroscopic Telescope

Final 4MOST Wide Field Corrector lens delivered

by Joe Liske on 2021-07-19

The Project Manager, Joar Brynnel, is very happy to report that on 2021-07-15 the large lens "L1" for the 4MOST Wide Field Corrector (WFC) arrived safely at the UCL laboratory. Being the largest (900 mm diameter) and most expensive optical element in 4MOST, this is the final WFC lens to arrive in London.

The raw material (so-called "blank") for this lens was procured from a US vendor in 2017, and then shipped to an optics manufacturer in New Zealand. Here the lens was machined, and in August 2018 it was shipped to a specialist in the US for the so-called aspherisation. This is a difficult manufacturing step that only very few suppliers worldwide are capable of, especially for a lens of this size. For various reasons, the aspherisation took much longer than anticipated, and the lens was returned to New Zealand only in November 2020. Here, the lens was thoroughly tested and found to be in spec. In December 2020, the lens started its next overseas journey, this time to a coating facility in the US. The optical coating was completed and accepted in July 2021, and the lens was then shipped to London where it is now safely stored and waiting to be integrated into the WFC. We are relieved to finally see this beautiful lens finished and having survived the long journeys across the planet!

The L1 lens in its shipping box during its incoming inspection at UCL.