EYEPIECE DESIGNS Last updated: 28 April 2001

Subject:	Reassembling an Eyepiece
Sent:	Thursday, April 26, 2001 08:13:33
From:	sherrodc@ipa.net (Clay Sherrod)
To: Jim 
Ohhhhh, Jim.
Let me ask you (did you get the lenses mixed up as to which one goes at
the eye end and which one goes at the bottom......or did you simply
forget which way they are turned in the eyepiece tube?)

In "theory" you will have two (2) sets of two cemented lenses.  BOTH
should be identical, and one group of two goes at the top and the other
at the bottom.  Now....you will see that each shows one (1) concave
surface and one (1) convex surface.  Assuming that Meade's Plossl is the
classic design, merely insert the top one first, with the CONCAVE
surface closest to where you eye would be....the convex surface, then,
would be aimed into the tube of the eyepiece.

Now the lower element....the one nearest the base of the eyepiece is
inserted also from the bottom but opposite....in other words put the
convex surface in first so that it faces the OTHER convex curve from the
first lens group.  This will result in the CONCAVE surface of this lower
lens pair to be facing out the BOTTOM of the eyepiece.

There is a possibility that Meade's design is different, but I don't
think so.  If you know which one is top or bottom, all the better,
because BOTH CONVEX SURFACES FACE EACH OTHER inside the eyepiece tube
and BOTH CONVEX surfaces are looking "out of the eyepiece" in opposite
directions in a Plossl...

Good luck, and you owe me a steak dinner.

Dr. Clay

-----Original Message-----
>From: Jim
>Dr. Clay,
>
>I disassembled my Meade 4000 Super Plossl 26mm eyepiece to remove a speck of
>lint/dust right inbetween the two elements, and......you guessed it.......I
>got called away by and "emergency" and when I came back, I couldn't
>remember the order in which the two elements went back into the eyepiece.
>
>I don't notice any appreciable difference between the two elements.  I do,
>however, notice that there is a line etched around the circumference of each
>element.  This line is closer to one side of the element that the other.
>
>Is there a specific orientation for the elements?
>
>Thanks,
>
>Jim.

As a follow-up (I like to triangulate my information!), I just located
this very informative illustration below on the web at funsci.com.  It
confirms your assessment and my configuration.  The Plossl Eyepiece is
depicted near the bottom of the page.

As a kid, I loved Christmas because I knew I'd be getting new things
that I could take apart!  Thankfully, some of us never grow up!!

Sincerely,

Jim.

And more:

Jim -
that diagram is absolutely correct and the lens elements need to be
arranged in that fashion.  Unless Meade has made some "custom changes"
which I doubt.....it does not matter which pair are placed where in your
eyepieces as long as they oppose one-another as clearly shown in your
diagram..   A picture is worth....an eyepiece!

Clay Sherrod

And this:

I did not mix them up as to top and bottom element.  I just couldn't
remember concave/convex orientation.  I reasoned the configuration you
suggest and tested the eyepiece last night on a terrestrial object last
night (a distant neighbor's electric meter) and could easily read the
dial indicators on the meter from 150 yards away.  I then star tested
the eyepiece on Sirius and got a nice pin point focus.  I guess I got it
right.

So, go on down to your local Outback Steakhouse, order up whatever you
want, and tell them Jim on the island of Saipan will come by later and
pay them for your meal.

Thanks, again.

Jim
Saipan, Northern Mariana Islands, USA
15' 09"N  145' 44"E  GMT +10

Jim - they told me your credit was great and they had a direct link to
Saipan.  "Order whatever you want..." they said.  So my Meade 16" is due
here probably in about two weeks.  (Steak was good, too!)

Glad you got the eyepiece back together well.  You figured right!

I am glad I could help.

Clay Sherrod

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