----- Original Message -----
From: "Shough, Dean" <[EMAIL PROTECTED]>
| > Wouldn't a significant part of the weight savings come from a reduction
in
| > the amount of glass in the lens? It seems to me that a DO lens could be
| > extremely thin, since the light-bending is being done by the diffraction
| > grating rather than by the refraction of a varying thickness of glass.
In
| > other words, the DO element could be essentially flat, as opposed to a
| > conventional element that's convex, concave, or some combination
thereof.
| >
|
| The glass is typically a small part of the overall weight of lenses. The
| main weight savings comes from the extra degrees of freedom that allow the
| optical designer to reduce the length of the lens. Look at the 200 mm
| F/1.8, 300 mm F/2.8 and the 400 mm F/4 (the unreleased lens the DOE lens
was
| compared to). Each lens is approximately 100 mm in diameter and similar
| design, but as the focal length increases the length and weight increases.
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.
Bob Turner
Dundee, Scotland, U.K.
Website : www.bawbee.co.uk
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