How do you identify a Plossl eyepiece?

On 6 Sep 2003 13:42:07 -0700, (Doc) wrote:

How do you tell if you have a Plossl eyepiece?

Thanks

Not easy unless you take it apart to look - not really recommended but
if you feel comfortable about it... (just remember to put things back
exactly how they come out!).

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. You can normally see if each lens is a doublet by looking at
their edge, you'll see a line where the two components are cemented
together.

ChrisH

UK Astro Ads: http://www.UKAstroAds.co.uk

"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.

..

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

UK Astro Ads: http://www.UKAstroAds.co.uk

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.

Hmm, well, from what I remember being told, a plossl needn't be plano;
just that the _most_ convex surfaces are facing each other. In reality,
if I remember correctly, that means the crown (convex) halves of
the achromats are facing each other. But I'd be interested to hear if
this is wrong.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk