Joseph Tainter wrote:
David asked:
* ED glass has suddenly become cheap enough to use in a broader range of lenses.
* ED glass has become necessary to produce acceptible results with DSLR's.
* ED glass has become enough of a recognized feature that using it pays dividends in improved lens sales.
* Pentax has become committed to producing better zooms than ever before, possibly to try to close the door on 3rd party lenses (much like SMC does).
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I have wondered if ED glass is now less expensive to produce. Mentioning its presence is certainly an advertising point.
Knowing what little I think I do about it... I wouldn't think so.
You don't just call an optical design an ED design. The particular glass formulation must match some particular optical design. They have to go hand in hand.
The glass they use is 'doped' to obtain the refractive index they're searching for, for some given lens design.
Once you have the design, all the ED glass doping, manufacuring and testing takes place at the glass foundry, and I should think it essentially never changes for that particular R.I.
What I'm saying is, you don't just casually decide to offer ED glass in a lens design. Any number of factors might change, and have to be accounted for.
Other production and ingredient costs may well change, and probably do, but not the process itself.
So it seems to me.
keith whaley
