[AZ-Observing] Re: The Orion 120mm ED Refractor
- From: Brian Skiff <bas@xxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Mon, 7 Aug 2006 16:52:25 -0700 (MST)
>> I read that as two objective elements, making it a doublet. There's a lot
>> of confusion over the terms APO, ED, and Achromat, triplet etc.
Since there are experts on the line here, am I correct in thinking
that there is no "in-between" range of color correction amongst
refractors? That is, the ordinary doublet has a color error of
something like 1:2800 of the focal-length of the telescope, and
"apos" have error of around 1:10000 or smaller --- with nothing
in-between except by purposely mis-designing an "apo" to have worse
correction than you would get naturally (more-or-less). I presume
that since the optical materials is a pretty mature technology that
nothing's changed in the last 10 years as far as materials go.
\Brian
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