keith_w wrote:
Godfrey DiGiorgi wrote:
On Sep 12, 2005, at 1:42 AM, mike wilson wrote:
A "large parallel cylinder of light" is the same thing as light
coming from an infinitely distant point source. Consider light from
the sun: all rays are parallel at 92 million miles distance, unless
scattered by atmosphere. In the vacuum of space, they are absolutely
parallel. So even though the sun is several hundred times the
diameter of the Earth and is a light source, it is a point light
source.
Point of information: 8-)
The sun's light rays are not parallel. If they were, then it would
appear the same size at whatever distance you saw it. Think of a
laser spot from a pointer. Apart from atmospheric diffusion and the
flaws of production, the spot should be the same at one foot, one
hundred yards or one mile. _Because the sun is so far away_, the
light rays are very close to parallel. But they are not.
True, point taken. But they are very close to parallel, the deviation
being extremely small across so short a distance as the diameter of
the earth. I should have written "... all rays are 'effectively'
parallel at 92 Milliion miles distance ... ".
Godfrey
He may indeed have scored a point, but the net result is, it doesn't
really matter one tiny bit. It's calculable, but not observable...
No point scoring involved; just making a small clearup of detail. SMC
coatings are about 1/4 of a wavelength of light in thickness - you can't
see the difference _they_ make?
No-one on earth can measure the difference in angles involved, and for
certain, no-one would actually SEE any difference in his photography,
so...it's argument for the sake of argument ~ period.
I would have to disagree with you there.......
keith whaley ;-)
Indeed.
