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ED Design?
Here's a thing that puzzle's me and probably says more about my ignorance of optics that anything else.
The price of an ED is considerable higher than an Achro of similar size because essentially the glass is dearer.
So my question is, "Instead of using a large lens in the primary doublet/triplet as the ED element and thus adding to the cost, why can't the designers use a smaller correction lens toward the end of the light path that would use about a 1/3 of the glass a front element would use?"
My own presumption is that the light still needs some distance beyond the lens to bring all frequencies to a common focus, just less than the standard achro configuration. Right, or wrong?
Trevor
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