这里是Astro-Physics老板和设计师Roland Christen的原话:
Just today I was reading an ad for an "ED" eyepiece. It said the following:
Our ED-2 eyepieces are made of "extra-low dispersion optical glass that boasts
superior refractive properties ..." etc.
Well, I'm a long time optical designer, and frankly, using real ED glass in an
eyepiece is a total waste of time. This material produces nothing that other,
better suited glasses cannot produce in terms of field width, sharpness, color
correction and a host of other properties. In fact, I'm willing to bet that
they are using FK5 and calling it "ED" glass. This material has been used in
various wide field oculars almost since the beginning of time. We optical
designers call it "fake ED". It does not have any property that could be
attributed to real "extra - low dispersion" materials.
Hang loose,
Roland Christen
Astro-Physics |