Re: ATM Advice on Large Spherical Mirror? - UNIFORM ILLUMINATON

["Richard Schwartz" <richas@earthlink.net>]

----- Original Message -----
From: "David Sleeter" <d.sleeter@verizon.net>
To: <atm@shore.net>
Sent: Wednesday, December 05, 2001 7:51 PM
Subject: ATM Advice on Large Spherical Mirror?


(snip)

>  The ronchi lines look reasonably
> straight, but it's hard to get an excellent read, because my Focault
> tester uses a cheapo "grain-of'wheat" bulb. The image of the filament
> shows through the pinhole, and it distorts the appearance of the ronchi
> lines.

Aha, gotcha!  It seems that non-uniform illumination really can and does
happen!   After all, we are working with a pinhole camera here.   What about
Mutalib's question on how to calculate the knife edge longitudinal shift
when trying to balance unequally illuminated aperture masks?

I am thinking of those hemispherical diffusers that old school black & white
photographers of the Weston and Adams generation used on their light meters.
This would be placed behind the pinhole and illuminated as uniformly as
possible.  But like everybody else around here, I have no idea how to
calculate anything related to this.

. . . Richard