Warning, possible "dumb question" coming...
I'm looking at doing some piggy-back DSLR work and moving up to an ED scope. It occurred to me that there's not much difference in focal length between a lot of telephoto lenses and the smaller ED scopes - eg 400-500mm.
Now I know ED scope are good for eliminating CA... but what is the deal with most telephoto lenses... are they effectively like achromatic refractors or does the coating achieve similar CA inhibiting results
cheers,
Rob