ATM Foucault & Pinhole Camera?

["James Lerch" <jlerch1@tampabay.rr.com>]

Greetings All,

I've been pondering ways to do a Full surface Foucault test, and the thought occurred to me to try a Diffuse light source, and a Pinhole camera.

I tried, However my skill at making a pinhole camera is lacking, but the initial results looked promising.

Before I put more effort into this, I thought I would pass my hypothesis by the Wise and All knowing list.

Given:

#1 A Pinhole camera, with a Properly sized pinhole to match a ~monochromatic light source
#2 An unobstructed diffuse light source, Co-planar with the Pinhole (a flat tipped, frosted LED)
#3 All mounted on a X-Y platform, where Y motion is Parallel to Optical axis

If the pinhole is at the null position for the 50% radius of our parabolic mirror, only the bundle of light from the 50% radius will be focused small enough to make it thru our pinhole.  Light that focuses Closer or Further away from the pinhole will be substantially reduced.  

The result on our CCD camera will be an image of our mirror, with a bright ring of light at the 50% radius.

I'm almost too embarrassed to show this, so please excuse the Crap on the CCD, the poor focus, and pinhole irregularities, but it does show the idea may have merit

http://lerch.no-ip.com/atm/pinhole.jpg (11kb)

The above image is nulled near the 75% radius for this mirror, a 6" F/5.  Any idea why there is a vertical component going diagonally from lower left to upper right?  

The camera used is a Philps Vesta Pro, with a Pin hole made from Al foil, spaced roughly 19mm from the CCD.  The light source is a 5mm diameter LED, sanded flat.  

BTW, you can definitely see that the surface of my mirror is rather rough at this null, on regular Foucault, you can only see this in the Center of the mirror, where its near spherical.

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My Bino-Scope Documentary)





Take Care,
James Lerch
http://Lerch.yi.org/atm (My Telescope  Construction Webpage)