Mirror manufacturers need to have a dedicated "Test Tunnel". This will be a space set aside in the factory which is long enough to test mirrors and can be maintained at a very even temperature, while allowing easy access to the individual components of the system under test.
There must be no draughts or significant air convection as this implies there is a temperature gradient in the tunnel which will affect the results.
In our new factory we have several test tunnel positions, - the one in the photograph opposite is along one of the walls. It is a continuous timber bench, waist high and about 24' long.
Optical Test Bench being set up for a Cassegrain double pass test.