Re: [Phys-l] Sun's image due to reflecton by not a pinhole.

[Gary Karshner <gkarshner@stmarytx.edu>]

Bernard,
        This reminds me of one of my favorite papers, in which Lord 
Rayleigh calculated the focal length of a pinhole that had the resolution 
of a four inch telescope. It is something like 150 miles. One of my 
students pointed out to me last year that it was Aristotle who first 
noticed the imaging effect of a pin hole by observing that the spots of sun 
light on the ground under a leafy tree are images of the sun. This is 
especially evident during a partial eclipse of the sun when the round dots 
become crescent shaped images of the partially cover solar disk.
Gary


At 08:53 PM 4/29/2009 -0700, you wrote:
> Intuitively, I think a small plane mirror will act "like"  a pin
> hole.  A member of tap-l claims that a large mirror (eight inches
> diameter) will do the same if the "focal" length is long enuf.
> (logically meaningless).  He then backed it up by experiment.  i.e.
> nice image at 50 feet.
>
> My calcs. (remember I'm maths challenged) predict that image was ~
> five inches and (with ray tracing, trig, and algebra) the "circle of
> confusion the same as the radius of the mirror (what ever the
> distance).  So am I very challenged or is the tapper ...?
>
> bc
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