Aha, thanks Chuck - it's Fred Winterbottom 1 Piers 0. Don't bother telling
me the difference between diffraction and refraction, spare me the shame!
To my understanding, a telephoto lens one in which the distance from lens
node to focal plane is less than the focal length - and that pretty much
means what you say. Excpet, of course, that it is a zoom lens in question.
Piers
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of Chuck Norcutt
Sent: 29 January 2004 18:35
To: olympus@xxxxxxxxxx
Subject: [OM] Re: Diffraction Lenses
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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