see: <http://www.canon.com/camera-museum/tech/report/200106/report.html>
Essentially, Canon has have figured out how to manufacture a diffractive
element that has the inverse effect of normal refractive elements. They
use this effect to cancel out the chromatic and spherical abberations of
the normal refractive elements in the lens.
But I must be missing something here concerning surprise over a length
less than 4 inches (101.6 mm)in a 70 mm lens. The definition of a
"telephoto" lens is one which has a shorter physical length than its
focal length.
Chuck Norcutt
Woburn, Massachusetts, USA
Winsor Crosby wrote:
>
> I was alert enough to notice that Canon was flogging something called a
> diffraction element telephoto some time ago, but did not pay much
> attention. I was flabbergasted when they just announced their new
> 70-200 zoom with diffraction elements that enable a length of less than
> 4 inches at the 70mm end of the zoom.
>
> Anyone know how a diffraction lens works?
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