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I think you'll you'll find that the 160 ED is made with FPL53.
The 160 FL is made with Calcium Fluorite as the colour correcting element.
Its more expensive as it is more expensive to produce. The regulations governing its manufacture are quite strict (principally with regard to disposal of the toxic by-products).
As a BTW: Contrary to general belief CaFl2, which is a crystal, is much easier to figure than ED glass and can be produced in batches with very little variation from 'perfect'.
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