RE: ATM An $18.00 Null Test

[Ric Rokosz <bz737@freenet.toronto.on.ca>]

On Tue, 27 Jul 1999, Wagner,Rick [CIS-ISB] wrote:

> ing a single pass through the lens means the lens quality is somewhat less
> important.  Given any lens it should be easy enough to use a ray-trace
> program to minimize spherical aberration by adjusting only the mirror-lens
> and lens-knife edge spacings.

The lens quality is most important in these tests.The Dall has to be 
really good to work at all and the Ross is a bit more foregiving if you 
use only the central area of a large lens.

I used a surplus lens for a while and then made a custom Ross lens and the 
difference was  amazing - shadows were clearer and easier to see.

Ric