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All optical flats are flat to 1/10 wave, i.e. flat to 0.00005 mm.
The thickness of the flats is typically 1/6 of the diameter.
Tolerance on diameter +0/-0.25 mm.
All optical flats are supplied with a calibration curve in individual cases for protection of the surfaces when not in use.
A choice of three materials is offered :-
Fused Silica has an extremely low coefficient of expansion and is perfectly transparent. A higher grade of this material is available which is suitable for optical systems where the transmission of the flat is important. Flats of this material can be made to special order.
Zero Expansion Glass The coefficient of expansion of this material has obvious advantages but it does tend to be slightly yellow-brown in colour. The transmission is still very high and perfectly acceptable for normal optical flats.
Low Expansion Glass This glass is not a high quality optical material but it is perfectly transparent and very suitable for normal optical flats.
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