Re: [ATM] ATM - Schiefspiegler!!! - (really a question about lens curves)

["David Harbour" <stainless_steel@suddenlink.net>]

Looking for a really SIMPLE lens, with a real good focal length, without 
having to worry about radius of curvature?

Go down to your local vending optician, and ask for what you want in 
diopters, and amount of "reflex". For instance, say you really wanted a long 
focal length lens, that was only slightly "reflexed"; you would ask for an 
unprocessed (glass) opthalmic blank of  +.25 diopters. Better have a long 
tube for it; probably have to stop it down a little bit. (196" focal length)

I have some "rare" tubing, made by "Sparco" office products, that is almost 
the right diameter (the inside part is exactly right) for unprocessed 
opthalmic blanks; the beauty of this spiral wound, accurately made tubing is 
that one can slide the two very long pieces together, and they slide 
smoothly without any "runout" or sideplay, until one gets very close to the 
end of the the outside tube. I have a good little pile of these wonderful 
adjustable, robustly made mailing tubes on hand. Also, I have some truly 
large diameter tubing, same kind; don't know who made it, though. About 4" 
diameter; slides really smoothly, both pieces.

Look in the November, 1996 issue of Sky and Telescope for an application of 
this "Sparco" tubing. I don't think they make it anymore.  ("The Milk Crate 
Mounting" by David A Harbour, AKA "R-101")

R-101

----- Original Message ----- 
From: "Richard F.L.R. Snashall" <rflrs@rcn.com>
To: "ATM List" <atm@atmlist.net>
Sent: Monday, April 14, 2008 11:33 PM
Subject: Re: [ATM] ATM - Schiefspiegler!!! - (really a question about lens 
curves)


> Adam Perkins wrote:
>>
>>
>> I don't how common a convex element of +/- 80" radius
>> might be, but I'm hoping someone can point out a
>> correlation between EFL and curvature of exposed
>> elements in a "typical" achromat.  A simple lens would
>> be ideal, but beggars can't be choosers in the surplus
>> market.
>>
> Not surplus: JML Optical (www.jmloptical.com) has a lens,
> stock number 77898, which is a meniscus, one of the radii
> is a convex 2115.8 mm and its diameter is 63 mm.  The
> material is SF8 or similar, I think.
>
> Melles Griot had a doublet, LAO357, that had a similarly
> shaped SF8 flint element, but I cannot find it on their
> website.
>
>
>
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> 


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