[ATM] Re: Too Small Optics

["David Harbour" <scarab2@cox.net>]

Richard,

You and all the others already know the answser to this question. The errors
that occur on the surface of a lens during polishing out can be 400% larger
than the errors on a reflector objective, and still not be objectionable.
The four times error is a "rule of thmb". Nevertheless, it lets lensmakers
off the hook for testing (at least for small lenses). (I.e., they don't
really "test" them)

Now, not long ago, I sold a 6" Roland Christian lens, an f/12 apochromat.
This lens STUNNED ME with its performance. In 1988 (I think; someone correct
me if I disremember, here) I watched Saturn pass in front of that (3rd?)
matgnitude star, down south. The view took my breath away!! I was stunned at
the view at 475X (and angry that a friend begged, and I gave, eyepiece time
to, while the star was scintillating as the rings passed across it).

Now, I haven't made my point. At the time I bought my f/12 lens from Roland,
there was a "debate" of sorts, going on in the Kalmbach publication
(excellent; the idiots let it go): "Telescope Making" (I advertised my kit
mountings in it).

In any case, they showed a "nullograph" of one of Roland's lenses: I took it
as representative of his lenses. IT HAD HUNDREDS OF LITTLE ZONES IN IT: high
zones, troughs- stuff mirror makers WOULD HAVE NEVER ALLOWED.

I assumed that my lens must have been typical; and yet, there it was:
STUNNING  views of everything.

In the nasty exchange between John Gregory (who'd just come out with his
"wonder" lens- the two element apochromat which he claimed would outperform
Roland's lenses) and Roland, Roland claimed he was trying to manufacture
ultra high performance lenses that "amateurs could afford", rather than
something so exotic as John's lens, that no one could afford.

Who can afford Roland's lenses, now? I paid $1195 for mine; when I
advertised it in Astro Mart, I had a remarkable number of hits, and one guy
asked me what my highest bid was (I told him $2,200). He said: "Would you
take $3,500? I said: "I'll start packaging it for you now". (Wouldn't any of
you guys like to have deep pockets like that?). Now here is the interesting
part of the story: I had sold this lens to someone 15 years ago for $950. He
died; his brother GAVE THE LENS BACK TO ME. Thus, I bought it once, and got
to sell it twice. Somewhat wistfully, I wish I had it now.

Lensmakers have it easy. It us us mirror makers, who deal with real
precision, who are really challenged. Don't forget it, guys.

Dave
----- Original Message ----- 
From: "Richard Schwartz" <richas@earthlink.net>
To: "David Harbour" <scarab2@cox.net>; "ATM List" <atm@atmlist.net>;
"Richard" <cnc@cncservo.co.uk>
Sent: Wednesday, June 15, 2005 2:08 PM
Subject: Too Small Optics


> Dumb Question:  how do they test and figure microscope lenses?
>


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