Wikipedia is a good read

[RobF]

I was just browsing the eyepieces entry in Wikipedia. Really well written piece for someone who still marvels at the quality and variety of astronomical products available these days compared to the very early 80s. http://en.wikipedia.org/wiki/Eyepiece

The diagrams of the various eyepiece designs very informative. Can still remember reading Patrick Moore textbook descriptions of Kellners etc and wondering what they'd be like. Now we've got Ethos, Pentax, etc etc.

Happy time to be a visual or photographic astronomer.

[RickS]

If you enjoyed that, Rob, you'd probably like the chapter on eyepieces in the book "Telescopes, Eyepieces and Astrographs" by Smith, Ceragioli and Berry. The spot diagrams demonstrate the performance of each eyepiece design very clearly. I found it very interesting to see the steady and significant improvements made as eyepieces evolved over time

The rest of the book is very good too...

Cheers,
Rick.

[RobF]

Thanks Rick. I need to read up on spot diagrams more. If I understand correctly, almost like a statistical modelling of where light of given wavelengths can be expected to fall?

[RickS]

Rob,

A spot diagram is the result of ray tracing a bunch of rays representing a point source to see where they fall on the focal plane. As you suggest, this is often done in a few discrete wavelengths. So long as they all fall within one pixel I'm happy ;)

Having read the book I'm now a big believer in ray-fan plots. They make it pretty easy to "read" what aberrations are present in a scope design. Unfortunately, I've never seen a scope manufacturer supply one...

Cheers,
Rick.