>
> Answer the bloody question Dr Wayne -
>
Yeah, well I forget the details (1st or 2nd year uni some 35 years ago) but
I seem to remember something about it. We all seem to agree that the light
intensity from a point source falls off as 1/r**2, if you put a lot of
points together in a line the light intensity drops off as 1/r (I seem to
remember you can "prove" this by integrating along a line from x = -infinity
to +infinity). Extending this by putting a lot of lines parallel and close
to each other would probably give you the 1 required (integrate the
intensity from the points from x= -inf. to +inf. and y= -inf. to + inf.).
Of course practically the plane of light is not infinite but it's probably a
close enough approximation since the part of the plane outside the field of
view of the lens doesn't contribute any light to the image anyhow.
Did a quick check of Halliday & Resnick which shows this for electric field
strength from an infinite sheet of electric charge so it probably holds true
for any physical attribute which exhibits a 1/r**2 relationship for a point
(e.g. gravity too).
...Wayne
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