Re: ATM Immersion Null Test for Aspheres

[Scott Rychnovsky <srychnov@chem.ps.uci.edu>]

>Recently while thumbing through old optics journals I came across a letter
>by Robert T. Holleran originally printed in Applied Optics Vol. 2(12)
>1336-1337 (Dec.  1963) entitled "Immersion Null Test for Aspherics".  The
>author presented what he believed to be a novel null test for aspheric
>surfaces.
>
>
>For a paraboloid where e = -1 this translates to a value of 1.414 for n.
>Some oils have indices near this, however the letter notes that this
>nulling method, when used on shallow curves, can tolerate wide parameter



Anthony,

I was interested in this method for a while, but then I put together 
a Waineo null test setup and haven't looked back.  One problem of the 
method is that you need to work vertically, which may be tricky for 
long focal-length paraboloids.  I did take the trouble of looking up 
some likely fluids for null testing, however.

The most promising fluid I found was diethyl malonate.  It has a 
refractive index of 1.4140 (20 °C), is relatively non-toxic , and is 
also relatively cheap by the standards of fine chemicals: $33 for 1 
Kg (one could probably find a better price.)  It has a high flash 
point and a high boiling point (199 °C) , which makes it relatively 
safe and convenient to handle.

Let me know if you decide to try it.

Scott

--
Scott Rychnovsky
srychnov@chem.ps.uci.edu
ATM Page: http://www.mindspring.com/~tlepage/