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Modern optical telescope use mirrors and very few lenses.
Unlike bathroom mirrors, where the shiny layer is sealed in to the back of the glass, telescopes use so-called “first surface” mirrors, with the reflective layer on top. This makes them difficult to clean.
When they get dirty or as they loose reflectivity over time, they need to be re-aluminised. Professional telescopes in constant use, need their mirrors to be re-aluminised roughly every two years.
The word “aluminising” suggests that aluminium is involved - which is indeed the case. A very thin layer of very pure aluminium gets deposited onto the mirror’s surface in a special vacuum deposition process. This video shows this process in detail, from beginning to end.
Because aluminising is a fairly unique process, but since it is needed at every observatory, it is therefore commonly found at observatories. The South Africa Astronomical Observatory is no exception, and has a total of four aluminising tanks of different sizes, ranging from 330mm (13 inches) to 2 metre diameter.
In this video we will be using the tank capable of handling up to 40-inch or 1 metre diameter mirrors in which we will be aluminising a mixture of professional and amateur mirrors - 5 mirrors in total.
31 авг 2018
