I wrote earlier:
<<The new issue of EOS Magazine carries an article on the DO lens. I don't
have it here with me but from what I remember, from my quick look, the set
comprises two unmarked glass elements with a 'marked' element sandwiched
between them. I will have another look soon and revert back to the list.>>
In fact there is not a sandwich.
To quote from EOS Magazine
"..... Diffractive gratings are already used in spectroscopes and in the
optical-reading systems of CD and DVD players.
Until now, diffractive elements have not been used in camera lenses because
there is a tendency for white light to produce superfluous diffracted light
as it passes through the grating. This results in flare, which degrades the
image quality.
Canon has resolved this problem by creating a multi-layer condtruction made
from two single-layer diffractive optical elements with opposing concentric
circular diffraction gratings. When incident light enters the element,
superfluous diffracted light is not produced and almost all of the light is
used for the image. This makes it possible, for the first time, to use a
diffractive optical element in a camera lens."
There are diagrams indicating the opposing gratings matching each other,
rather than being etched on the surface. Please see the December issue of
EOS Magazine for full details.
www.eos-magazine.com has not been updated to include the articles in the
current edition, maybe Robert will make this article as a PDF for
downloading?
Bob Turner
Dundee, Scotland, U.K.
Website : www.bawbee.co.uk
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