Aluminizing
It is best to defer the aluminizing until the cell and other tube parts have been completed; then the mirror and diagonal can be coated at the same time.
In Chapter XI, aluminizing and care of the optical parts are treated in detail.
Any but a perfect job of aluminizing should be rejected. If you are willing to go to the trouble and expense, it is a good idea to have the aluminized mirrors, especially the secondary, given a coating of magnesium fluoride — the same as is applied to the surfaces of lenses to reduce reflection losses.
This gives a hard, durable surface that will withstand considerably more cleaning than the softer aluminum, without affecting its reflective qualities.
Chapter VII The Diagonal
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