Thanks for your comments Daryl. I’d say if you spend much time looking at the Moon and planets, or double stars, an ED refractor is a very worthwhile upgrade from a standard doublet. The resolution and colour perception are both substantially enhanced by the almost total lack of chromatic fringing. The other advantage is an ED can be made shorter for its aperture and still give good images. The standard 100ED refractor is f/9, but its performance is better probably than a normal 100mm doublet at f/13.
- This reply was modified 3 weeks, 2 days ago by David Arditti.