[LargeFormat] Carl Zeiss Dagor 180mm f9

[Mike Brown]

Does anyone know the serial number sequence for Goerz, Berlin prior to 1926 
when it was absorbed by Zeiss?  I would like to assemble a serial number 
range correct year of mfg for the Goerz, Berlin manufactured lenses.
----- Original Message ----- 
From: "Richard Knoppow" <dickburk at ix.netcom.com>
To: "f32 Large Format Photography Mail List" <largeformat at f32.net>
Sent: Saturday, October 01, 2005 12:06 AM
Subject: Re: [LargeFormat] Carl Zeiss Dagor 180mm f9


>
> ----- Original Message ----- 
> From: "Timothy Atherton" <tim at KairosPhoto.com>
> To: "Richard Knoppow" <dickburk at ix.netcom.com>; "f32 Large Format 
> Photography Mail List" <largeformat at f32.net>
> Sent: Friday, September 30, 2005 9:51 PM
> Subject: RE: [LargeFormat] Carl Zeiss Dagor 180mm f9
>
>
>> Thanks Richard, tons of info.
>>
>> I borrowed one of a colleague for a while - it's a very very nice lens 
>> (it
>> was probably later rather than earlier and was in a COmpur shutter). 
>> Someone
>> was telling me it was a Protar III just renamed after Zeiss bought Goerz,
>> but I didn't think so.
>>
>> tim a
>
>   There is a story to this. At about the same time that Emil von Hoegh was 
> designing the Dagor Paul Rudolph was working on a similar lens. Rudolph's 
> lens was also a double meniscus type with each half consisiting of three 
> cemented elements but, in Rudolph's lens, the powers were in a different 
> order. In the Dagor the outer elements are positive with the negative 
> element sandwiched in between. Rudolph's version had the positive element 
> in the center sandwiched between two negative elements. Actually, von 
> Hoegh also covers this arrangement in his patent. von Hoegh got precidence 
> on the patent but Rudolph also was able to get a patent on his version. 
> Now, an interesting thing is that before he he took his design to 
> C.P.Goerz von Hoegh approached Zeiss. There is a cute story that von Hoegh 
> was carrying a Christmas goose under his arm for his family and was not 
> taken seriously by the Zeiss people. I think it is much more likely that 
> he was rejected as a Zeiss designer because Rudolph knew von Hoegh had a 
> rival design to his own. Zeiss did make some lenses of the Rudolph pattern 
> as "Triple Protars" but never pushed the design much. The Schneider 
> Angulon has the same arrangement of powers as the Rudolph design but uses 
> oversize outter elements to get around mechanical vignetting. This is not 
> a problem when von Hoegh's arrangement is used because it results in a 
> shorter lens with less vignetting. There are other arrangements of three 
> cemented elements in a double meniscus lens. The best known of these is 
> the Voigtlander Kollinear. Curiously, there was another case of 
> simultaneous and independant invention here, Steinheil also came up with 
> the same design at about the same time. Steinheil called his lens the 
> Orthostigmat. Patents were issued to both companies and actual lenses 
> sometimes have the other's patent number on them. Evidently they 
> cross-licensed their patents. None of the alternative forms has any 
> advantage over the Dagor. The type has one fault: a large residue of zonal 
> spherical aberration. This results in some softness when used wide open 
> and some focus shift when stopped down. Actually, the blur due to the 
> spherical is of a pleasant nature so Dagors are useful as mildly soft 
> focus lenses when used near maximum aperture. Spherical aberration is 
> proportional to the stop so Dagors in all variations become very sharp 
> when stopped down about three stops. All double meniscus lenses are 
> inherently wide angle lenses. Plain Dagors will cover (barely) 87 degrees 
> at f/45.
>   A single cell of a Dagor can be used alone but the correction for coma 
> is dependant on symmetry so single cells must be used at quite small stops 
> to be reasonably sharp, around f/36 being the maximum.
>   The Zeiss index is a compendium of lens designs put together mainly by 
> Willie Merte, one of the great Zeiss Designers. It includes all sorts of 
> lenses made from around the late teens to the late 1930's. This internal 
> document was captured after WW-2 and published. The lenses in it are 
> included in the lens design survey program LensView, which I am fortunate 
> enough to have by courtesy of its author. The Zeiss Index shows that Zeiss 
> was evidently quite interested in the Dagor design and there are many 
> variations of it included. Zeiss had a rival design which was introduced 
> not long after the original Dagor. This is the Convertible Protar. As 
> mentioned above while Dagor cells can be used alone for long focus lenses 
> they are not corrected for coma. Coma is corrected by symmetry so a 
> complete Dagor has very little but the individual cells have a lot. Paul 
> Rudolph decided that by combining an "old glass" and "new glass" pair in a 
> single cell (by cementing them, 4 cemented elements in each cell) he could 
> obtain a true convertible where each cell was corrected for coma. 
> Convertible Protar lenses were sold in sets of up to five cells of varying 
> focal length along with a barrel and shutter. By using the cells alone or 
> combining them a great variety of focal lengths could be obtained along 
> with good performance. Used combined the Convertable Protar has no 
> advantage over a combined Dagor and maybe less coverage, but individually 
> the cells perform much better.
>   Modern large format lenses and enlarging lenses are often of a type 
> which traces its ancestery to the Dagor. This type is called the Plasmat. 
> In effect, the Plasmat is a Dagor with the inner elements split off and 
> air spaced. The advantage is that the additional degrees of freedom allow 
> much better correction of the zonal spherical which plagues the cemented 
> meniscus types. Plasmats are also capable of excellent correction for 
> astigmatism and, like their prototypes, they are essentially wide angle 
> lenses. The first Plasmat type was designed by Ernst Arbeit of Shultz and 
> Billerbeck but the name comes from a lens designed by Paul Rudolph during 
> his second career for Hugo Meyer. Another older lens of this general type 
> is the Wide Angle Xpres (the regular Xpres is of a different type) made by 
> Ross, and the Zeiss Orthometar of Merte. However, because of the flare 
> from the eight glass air surfaces, this type of lens did not become 
> popular with designers until afte good anti-reflection coatings became 
> available after WW-2. Because air spacing can result in much improved 
> correction and cheaper construction than is possible with all cemented 
> lens designs such designs died out pretty quickly after coating became 
> available.
>   von Hoeg, by the way, was also responsible for the "dialyte" type lens. 
> The first was his Celor but the type was perfected by designers such as 
> Walther Szchokke, of Goerz, who designed the Dogmar and famous 
> Apochromatic Artar, which are of this type.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk at ix.netcom.com
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