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[OM] Re: Diffraction Lenses

Subject: [OM] Re: Diffraction Lenses
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Thu, 29 Jan 2004 13:34:50 -0500
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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