At 3:28 AM +0200 4/13/04, Listar wrote:
>From: "David Irisarri" <div2000@xxxxxxxxxxxxxxxxx>
>Subject: [OM] Re: Please help - I want to buy E-1 system
>Date: Mon, 12 Apr 2004 23:11:53 +0200
>
>
>Fixed focal lenses shoud be at least f2 for the new E-system!
>
>And I would like to see a new 85/1,2 lens. (42.5/1,2) I think
>Olympus made a prototype many years ago of one 85/1.2 using
>special glass, called "grin glass" or something like that!
It's "GRIN glass". GRIN stands for GRadient Index of Refraction.
A GRIN lens is typically a flat piece of special glass that nonetheless can
focus light into images, because (unlike standard optical glass) this special
glass has a refractive index that varies with distance from the optical axis.
The variation is parabolic, with the higher refractive index in the center.
Multimode optical fibers are in fact elongated GRIN lenses made of fused silica
glass. Typically, the germanium-doped core is 50 or 62 microns in diameter,
and the overall fiber (including the pure silica cladding glass) is 125 microns
(1/8 of a millimeter) in diameter.
Small (a few millimeters in diameter) GRIN lenses are widely used in fiber
optics, and in xerox machines. I've never seen a GRIN lens big enough for a
camera lens. The chemical process that makes the carefully varying refractive
index profile is a bit tricky, and works best with small diameters.
My guess is that it turned out to be too expensive to make GRIN lenses both
large enough and accurate enough for a 35mm camera lens.
Joe Gwinn
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