Re: ATM Foucault test accuracy

[spooner@page.az.net (Michael Spooner)]

One thing I've wondered about is if the background is not uniform behind the
mirror. Also if there is glare from the knife edge area will it bias the eye
to one side or other for shadow comparison? As I age it becomes more
apparent why my parents used to complain about dirving at night and glare -
it's pretty amazing how much it now bothers me. Perhaps we should pay a bit
more attention to our testing circumstances and the effects of a varied
background illumination (and one sided knife edge glare) on separated
contrast comparisons. Food for thought anyway.
--Mike Spooner
----- Original Message -----
From: Tom & Lou Krajci <krajcit@3lefties.com>
To: <atm@shore.net>
Sent: Saturday, June 09, 2001 1:44 PM
Subject: Re: ATM Foucault test accuracy


>
> > From: "Bill T." <twentiethwave@hotmail.com>
>
> The user has to judge the *brightness* of two *separated* patches of
> light...and adjust the test apparatus so that the two patches are equal in
> brightness (and ideally at 50% of max illumination).
>
> Our eyeballs are not all that good at measuring brightness in absolute
> terms, and are a bit better at relative measures (but with the foucalt
test
> the two areas we want to compare are sometimes not that close to one
> another...making comparison more difficult and potentially less accurate).
> (CCD/video camera based test rigs overcome much of this problem, but I'm
> assuming we are making eyeball powered test rigs here.)
>