At 11:17 AM 5/8/2002, Ben McCafferty wrote:
>While we're on the topic of Fresnel lenses, those of you in or near CA, take
>a trip in your Westy (RVC) to the Pigeon Point Lighthouse, about 15 miles
>south of Half Moon Bay.  You can take a tour, and they are one of the only
>lighthouses I know of where you actually get to go up into the top where the
>Fresnel lens is.  It is an order 1 lens (I think--it's the biggest one ever
>made), and is nothing short of spectacular.  Once a year, in November, they
>light the bulbs inside the lens and it is a working Coast Guard beacon for 2

The biggest (bigger than first order) was called a hyper-radiant.  There's
a first-order lens in the light at Seguin Is. Maine which you can visit --
but you have to get out to the island, and the caretakers have to be
around.  They're the "Friends of Seguin," not official keepers -- like all
US lights it's officially unmanned.

There's another large lens, not sure what order, in the Boston Science
Museum, but it's not lit and I don't think you can get too near it.

These -- the original Fresnel lenses are based on the same principle as the
modern flat ones, but they're made of individual curved prisms mounted in a
globular framework.  Worth a few million each...

david

--
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"