Refracting telescope question?

[Doug B]

Which lens in a refracting telescope inverts the image -- the objective lens or the eyepiece?

[Michael Steen]

I'm going to give this one a stab and risk being called an idiot by more knowledgable posters (Carlos), but any lens (especially convex) which focuses light to a point will invert the image.
Imagine the light coming in at the top and bottom of the lens. It gets bent so that the top declines downward, and the bottom upward. Depending on the focal length of the lens, those two beams of light intersect at a point--the focal point. But they don't stop there; they keep going. But now the bottom is on the top and vice versa. Hence the inverted image.
The objective lens certainly does this, but so do lenses in the eyepiece. When you add up the minimum # of lenses required to bring the image to a sharp focus in your eye, you still end up with an inverted image. Another lens could be added to flip it right side up, but that would cut down on light transmission, so for astronomical telescopes it's eliminated.
Hope this helps. (And I hope I got it right!!)