keith_w wrote:
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
But it's a gargantuan amount when you are talking about lens
construction. See my previous post on this matter.
m
