Re: ATM Immersion Null Test for Aspheres

["Richard" <richas@idt.net>]

There are mechancal advantages to subject test that make it
appropriate for very large thin mirrors.

(1) The mirror is tested flat on its back so that there is
no need for a sling, pegs, or other edge support.   This
eliminates potatoe chip deformation for thin mirrors.

(2) With the mirror immersed in a flud, some of its weight
is neutralized.   This eases the requirements on a submerged
flotation cell.

(3) Based on efforts at autocollimation on a fluid surface,
a viscous oil is probably a better fluid than water because
it would not be as sensitive to slight vibrations (around
here, whenever a rapper's car goes by).

. . . Richard


----- Original Message -----
From: "Anthony Stillman" <atmer@flash.net>
To: <atm@shore.net>

> 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".

> delta s = R * k^6 * e^2 / 16  = (y^6 * e^2 / 16 * R^6 *
lambda) wavelengths
>
> where y = k*R
>
> It didn't make sence to me either.

This looks like one of the residual terms in the power
series for 1-sqrt(1 - y^2), which is the formula for
sagitta.