[rollei_list] Re: Xenon is a Xenar!
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 28 Mar 2005 18:56:56 -0800
----- Original Message -----
From: "J Patric Dahlén" <jenspatricdahlen@xxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, March 28, 2005 3:20 PM
Subject: [rollei_list] Re: Xenon is a Xenar!
> >From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
>
>> The late version of this lens is shown in the 1955
>> edition
>>of the Kodak lens booklet from the _Kodak Reference
>>Handbook_. This is from the Retina IIIc so it may or may
>>not
>>be the later version Patric has.
>
> It's not. The pre-war 2,8/50 Xenon I have, has three
> air-spaced elements in
> front of the stop, and a cemented pair behind the stop.
>
> I looks just like the one on the picture to the left here:
> http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00BeZf
>
> /Patric
>
The Xenar appears to employ a standard trick of splitting
elements to improve correction. It is a Tessar where the
front positive element has been split into two less powerful
elements probably in an attempt to improve the performance
at f/2.8. The Xenon shown is interesting. The back cell is
the back of a Biotar, the front is superficially simiar to
the Xenar but really isn't. If you look at the shapes of the
elements you will find them different. It appears that in
the Xenon the second component of the Biotar has been split
and air spaced. Its hard to guess the purpose. Warren
Smith, in _Modern Lens Design_, shows a lens classified as
a Biotar with no cemented surfaces (p.320) and a lens with
three air spaced elements in front of the stop and a
cemented pair and air spaced single element behind the stop.
This is a near UV lens but its layout is similar (p.321).
Since the f/2.8 lens is obviously derived from the Tessar
the Xenar name is appropriate, since the f/2 lens appears to
be derived from the Biotar the Xenon name is appropriate.
Neither lens is similar to the Wynne lens.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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