Re: ATM Ross null-test

["Howard Banich" <hbanich@teleport.com>]

Klass,

I've used the Ross null test a few times. A powerful test that is easy to
interpret - a null is hard to mistake for anything else. The set up takes
some care so you don't mistake misalignment for optical errors, but once
everything is set I've found it more convenient to use than a basic
Foucault, Ronchi or poor mans caustic test. The quality of the lens is
paramount to have confidence in your results.

I found that using a combination of readings from a knife edge and from
Ronchi bands helps confirm just how good a null you've achieved. A good
looking set of straight Ronchi bands may show some very slight zones under
the knife edge, or more likely a touch of over or under correction. Judging
when Ronchi bands are exactly straight takes a little practice.

I used a friends set-up, but I plan to buy a quality Ross lens as soon as I
can afford one.

Howard
Forest Grove, Oregon

-----Original Message-----
From: k.honders <k.honders@worldonline.nl>
To: atm@shore.net <atm@shore.net>
Date: Monday, August 23, 1999 1:13 PM
Subject: ATM Ross null-test

>Hi all,
>
>        I am quite sure that several of you have experience with the
>Ross-null test.I am very interested in your comments about that test.
>
>Klaas Honders
>k.honders@worldonline.nl