Archived posting to the Leica Users Group, 1998/05/07

[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]

Subject: Re: [Leica] 6.8 Telyts
From: "Henning J. Wulff" <>
Date: Thu, 7 May 1998 22:50:46 -0700

>>You're right. All, or most, glass flows like a liquid, just slower.
>Myth. Glass is an amorphous crystalline solid, and does not flow, even
>over centuries.

One last comment on this. Leitz Wetzlar told me this thing about the glass
changing. I think they said that the glass changed; not that it flowed. The
same fellow also said that they had had a similar problem with one of the
glass types developed for the Noctilux.

Having taken over 30 physics courses in University, I am not sure I
understand this explanation either, as I am not aware of any way that a
glass can change without flowing other than darkening or changing colour.
On the other hand, with proper doping and mixing it is possible to make a
glass that flows at room temperature. We're not talking window glass here,
but glass that has substantial quantities of strange elements. I have heard
(note that this is heresay; I'm not stating this as fact) that the present
Noctilux has some glass that has nearly twice the specific gravity of
ordinary 'window' glass. This stuff is far from ordinary. On the other
hand, the performance of my Noctilux has not changed. The only other lenses
in my possession that have changed, of the couple of hundred I've had over
the last 40 years, are those I've whacked hard enough and those
(Rodenstocks) that have had elements that have disliked their cemented
buddies enough to have left them.

BTW, the 400/6.8 deteriorated to such an extent that a 400/6.3 Soligor
preset costing $59Cdn at the time outperformed the Leica lens, and, as
noted before, there was no mechanical damage to the Leica lens nor were the
elements separating or coming otherwise adrift. Leitz Canada and Wetzlar
both had a look at the lens (mid 70's).

   *            Henning J. Wulff
  /|\      Wulff Photography & Design
 |[ ]|