Re: Re[2]: ATM 8" f3.8 -- Worthy project?

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Richard,

>Here is a radical idea not found in authoritative books....
>what if, instead of a wire, you use a small spherical bead?
>Then you get the circular shadow, but not the vertical bar
>shadow.   The bead can be moved from side to side to allow
>testing of tilted or astigmatic surfaces.

Why not? It should be a very fine test for astigmatism, as you can measure around the 
whole 2 pi of a zone at once, and pick out the zonal astigmatism that e.g. Mel speculated 
would account for much of the "missing matter" of one-dimensional Foucault type testing. 
Trouble is suspending it at a well-defined point in space, without the support 
interfering with the reflected light and messing up the image.

>And if you replace the bead with a pinhole (the pinhole is
>an inverse bead), I guess you see an illuminated circle.
>Hmmm....

>And if you use a slit, I guess you see an illuminated circle
>with a vertical illuminated bar....  Hmmm....
>
>Please keep this idea secret, as it is not according to
>established orthodox dogma.

By all means try it! It should be a *very* rewarding exercise in wave optics to try and 
explain afterwards why it didn't work at all like expected...... 
At least I thought so ;-)

Nils Olof