Archived posting to the Leica Users Group, 1997/10/09

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Subject: Re: 35-70mm. R f4.0 ASPH Zoom
From: Larry.Zaks@DANA.COM
Date: Thu, 9 Oct 1997 13:25:52 -0400

Eric Welch <ewelch@ponyexpress.net> wrote on Thu, 09 Oct 1997 01:06:21:
Subject: Re: 35-70mm. R f4.0  ASPH Zoom

>Canon is as far as I know the only company that does the glass on plastic
>thing. And I'll bet they're not sharing. And besides, that's only for the
>consumer aspherics. And the old Noctilux is way too old (1966) to have such
>a hybrid type of element.
>
>Leica is using molded glass. The aspheric surface is not ground, it's
>molded to a finished surface.

FWIW, Canon uses 3 types of aspherical elements, polished, molded and replicated
aspherical lens elements.

My understanding is that polished aspherical lens elements are fashioned by
grinding and polishing glass to aspherical shapes which is the most expensive
and time consuming way to do so.  Molded aspherical elements are fashioned by
forming molten glass into an ashperical lens shapes and presumably the grinding
and
polishing process is either not needed or minimal.  Replicated aspherical lens
elements are fashioned by bonding 2 optical materials together (one of which I
believe is made of a polymer resin) to form an aspherically shaped lens element.

Also, I think that I read that other lens manufacturers may be using the
"replicated
aspheric" lens process although I do not specifically recall the company
mentioned,
although Tamron comes to mind.  Leica's heritage and legacy, I doubt that any
compromises in terms of lens quality and construction have been made if they
use aspherical elements that are fashioned in a process other than grinding and
polishing method.

Regards,

Larry Zaks