Mirror supporting substratum for e.g. terrestrial observation, has spacers defined between one set of recesses and/ or two set of recesses, where part of one set of spacers has width different from width of part of other set of spacers

摘要

The substratum (1) has two set of recesses (2, 3, 4, 7, 8) formed in a rear face (16), where the substratum is produced from a monolithic block of material including a lithium- aluminum- silicon type glass ceramic material. Set of spacers (5, 6, 9, 10) are defined between one set of recesses (2, 3, 4) and/ or the two set of recesses. A part of one set of spacers (5, 6) defined by the former recesses has width different from width of a part of other set of spacers (9, 10) defined by the latter recesses.