John Francis wrote:
On Mon, Sep 12, 2005 at 09:16:42AM -0700, keith_w wrote:
[...]
No-one on earth can measure the difference in angles involved . .
Oh yes they can. In fact it's quite easy to do, even with the naked eye (as long as you use a piece of smoked glass or some other sun filter). There's around half a degree of difference in the angle of light from one side of the sun to the other - that's why the sun appears as a disc instead of a point light source.
I don't know where this is going, but...your 1/2 degree equates to 0.00873 inches of horizontal displacement, per inch of distance from the emitter, which I am assuming is the rear face of the rear element.
Ain't much... keith
