On Sun, 7 Sep 2003 00:29:11 +0100, "OG"
wrote:


"ChrisH" wrote in message
.. .
A plossl is normally a pair of matching plano-convex doublets with the
two convex surfaces facing each other - close together but not quite
touching.

That would imply that the first lens surface at each end should be flat. Is
that right?

I suspect that this comes into the 'true but not useful' category.


Actually, it's in the 'interesting but wrong' catagory...

I went and had a closer look on the web and it appears the eye-lens is
not plano-convex but the outer (eye) lens has a concave surface.
Having said that, my Vixen 22mm Plossl (as written on the barrel)
definitely has a flat surface on this face of the eye lens. It seems
there are a lot of minor variants of the basic Plossl design which are
then (wrongly) lumped together and called 'Plossls'. The design I
descibed above is correctly known as a 'symmetrical' or 'dialsight'
eyepiece.

Here's an interesting monologue describing the development of eyepiece
designs over centuries:
http://www.brayebrookobservatory.org...fEYEPIECES.pdf
(lots of other interesting information on the root page-
http://www.brayebrookobservatory.org...LICATIONS.html
but someone really ought to do something about that background image!

Other interesting sites I found we
http://members.shaw.ca/quadibloc/science/opt04.htm
Which has pretty coloured scross-sections of eyepiece designs - but as
I said, I would not treat these as definitions.

http://www.bpccs.com/lcas/Articles/scope4.htm#eyepieces
Interesting basics on how eyepieces and filters work

http://www.observers.org/beginner/ey...s.freeman.html
Jay Reynolds Freeman's page on his eyepiece selection for different
telescopes.


ChrisH

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