[Leica] Televit-V

[John Collier <jbcollier@home.com>]

While researching the Novoflex, I came across a posting from Mr. Wulff
discussing how a Leica Televit-V 400 f6.8 went seriously soft on him over a
relatively short period of time. He went on to say that he had heard of at
least one other case of this. He speculated (as did Leica which he had also
sent the lens to have checked out) that the special glass in the elements
(only 2) was unstable and had "changed". Has anyone else heard of this or
have any more definite idea on the cause? Should we avoid old versions of
the 400 and 560? I am hoping that brighter minds than mine will be able to
provide a few answers.

John Collier

I have "cc" this to Henning so he is not taken by surprize by the sudden
popularity of his name.


Here are the relevant messages from the archives:


Date: 05-May-1998 02:52:22
From:  
Subject: Re: [Leica] 6.8 Telyts

The 400/6.8 on a VisoIII was always a real delight for me as far as
handling went. I shot birds in flight at 20 feet, which you could't do with
anything else (except may a Novoflex) before autofocus. Unfortunately, the
field curvature in my lens actually changed with time (and the lens got
less sharp), so I got rid of it in the mid 70's.

   *            Henning J. Wulff
  /|\      Wulff Photography & Design
 /###\   mailto:
 |[ ]|     http://www.archiphoto.com






Date: 05-May-1998 23:44:52
From:  
Subject: Re: [Leica] 6.8 Telyts

>> The 400/6.8 on a VisoIII was always a real delight for me as far as
>> handling went. I shot birds in flight at 20 feet, which you could't do with
>> anything else (except may a Novoflex) before autofocus. Unfortunately, the
>> field curvature in my lens actually changed with time (and the lens got
>> less sharp), so I got rid of it in the mid 70's.
>
>Anyone know how this could happen? "field curvature in my lens actually
>changed with time"

The explanation given to me was that some glasses (glass being a fluid) can
indeed flow enough in a normal span of years to cause this. Leica has used
a number of exotic glasses, and I was told that this might have been the
cause. Separation of the two elements had not taken place. One other person
has related the same thing (re: a 400/6.8) to me.


   *            Henning J. Wulff
  /|\      Wulff Photography & Design
 /###\   mailto:
 |[ ]|     http://www.archiphoto.com






Date: 08-May-1998 02:50:46
From:  
Subject: Re: [Leica] 6.8 Telyts

>>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
 /###\   mailto:
 |[ ]|     http://www.archiphoto.com