eye piece f/ should match objective f/,

In Rutten and van Venrooij's Telescope Optics, in the chapter on eyepieces, the second paragraph begins:

"A most important aspect of the eyepiece (self evident, but not always recognised by telescope users) is that the focal ratio of the light cone entering the eyepiece, fe/de, is the same as the focal ratio of the objective system,fo/do, when there are no other optical elements between the objective and the eyepiece. This equality of focal ratio has important cosequences, particularly in the off-axis perfmance of eyepieces."

I haven't seen anyone discuss this on the web. I wonder if anyone here is paying attention to this. Wadda ya know?

Thanks,Dan

>>>I haven't seen anyone discuss this on the web. I wonder if anyone here is paying attention to this. Wadda ya know?

Thanks,Dan
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What they are discussing is the light cone angle entering the eyepiece, simply that the maximum angle that the light enters the field lens is a function of the focal ratio of the telescope.

This is often discussed on the web, certainly by those of us who own F4 telescopes...

This is why an 20mm Erfle or Konig works quite nicely in an F11 refractor while it turns quite sour when used in an F4-F5 scope.

Certainly Al Nagler has capitalized on this with the Naglers being well corrected down into the F4 range.

Jon Isaacs