[rollei_list] Re: Xenon is a Xenar!
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 28 Mar 2005 14:47:23 -0800
----- Original Message -----
From: "Eric Goldstein" <egoldste@xxxxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, March 28, 2005 1:03 PM
Subject: [rollei_list] Re: Xenon is a Xenar!
> Sounds like an interesting variant Patric but the math is
> confusing me... t=
> wo cemented elements plus three individual elements is 7
> elements in 5 grou=
> ps total... no?
>
>
> Eric Goldstein
>
>
I think he means two elements cemented together not two
groups of two elements.
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. This is a 50mm, f/2.0, 9
element lens,, 4 components in front of the stop and two
behind it. There are three cemented components each of two
elements. All the glass-air surfaces are concave to the
stop, the cemented surfaces are either plano or near it.
This lens is part of a system where the groups in back of
the stop are part of the camera and the groups in front of
the stop are interchangible to change focal length.
Information on the construction of the Longar and Curtar
front cells are not given in this book but Kingslake shows
them in _A History of the Photographic Lens_. There are
three shown for focal lengths of 76mm, f/4.0; 48mm, f/2;
35mm, f/5.6. There is a puzzle here: the illustration of the
76mm cell is the one shown in the Kodak booklet as the 50mm
one. From Kingslake's descriptions his illustrations appear
to be right. If this is so the 48mm, f/2 "normal" cell makes
a conventional Biotar with the back element. Both the wide
angle and long focus cells have six elements in four groups,
but of somewhat different arrangement. Kingslake states that
two different systems were used, one based on the Schneider
Xenon, the other on the Rodenstock Heligon. Both of these
are Biotar types. Kingslake also says that the whole system
was abandoned in later cameras for complete interchangible
lenses operating with a common rear shutter.
Despite a claim by Marc Small that the Xenotar type lens
originated at Zeiss in the mid 1930's I can find no
indication of that anywere. No early lenses of this sort
appear in the Zeiss Index which is included in the LensVIEW
program. Kingslake attrbutes the design to C.G.Wynne of Wray
Optical dating from 1944, a lens called by Wray the Unilite.
These are derived from the Planar/Biotar by eliminating the
positive part of the cemented rear component and bending the
resulting negative element. The Unilite/Xenotar still has
symmetry so it has very good correction for coma, lateral
color, and geometrical distortion along with the flat field
and good correction for spherical typical of the Planar
derivatives.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
> -----Original Messag
e-----
> From: J Patric Dahl=EF=BF=BDn
> <jenspatricdahlen@xxxxxxxxxxx>
> Sent: Mar 28, 2005 3:53 PM
> To: rollei_list@xxxxxxxxxxxxx
> Subject: [rollei_list] Xenon is a Xenar!
>
> I have a pre-war Kodak Retina IIa (type 150) with the
> Schneider Xenon=20
> 2,8/50.
>
> I thought the lens looked much different from the post-war
> Xenon on my IIc.=
> =20
> The rear lens group is made of two cemented elements, and
> there are three=
> =20
> air spaced elements in front of the aperture.
>
> So this pre-war Xenon is actually the FIVE ELEMENT XENAR
> we have talked=20
> about on the RUG before. It's sometimes called
> "Super-Xenar" in Schneider=
> =20
> litterature.
>
> In "a lens collectors Vade mecum" they say: "This looks
> the same lens as th=
> e=20
> S-Xenar for Exakta from the reflections and external
> curves. Thus it is a=
> =20
> case where a triplet was used for a Xenon design [...]
> Perhaps Kodak merely=
> =20
> liked the prestige of having Xenon on their cameras".
>
> (Not the same as the S-Xenar on Rollei 35 cameras. That's
> a four element=20
> lens)
>
> /Patric
>
>
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