Giant coating plant for the VLT: a porthole view

View through a porthole in the VLT coating plant. The coating unit is a large vacuum chamber with a diameter of 9.4 meters and a volume of about 122,000 liters. The required ultra-high vacuum is generated by 8 cryo-pumps which are located on top of the vacuum chamber. The lower half of the vacuum chamber is mounted onto an air-cushion vehicle via 4 large spindles for closing and opening of the vacuum chamber. For loading and unloading of the mirrors the lower half of the chamber is moved on 8 air-cushions from the coating unit location to the mirror handling tool and vice-versa.