[LargeFormat] Goerz Artars

[Michael Briggs]

On 25-May-02 Guy Glorieux wrote:

.............
> I just recently purchased on eBay a
> "Goerz Apochromat Artar, 19", F:11- F:32, 
..........
> The seller also claims that it will cover 20x24, which would be ideal
> for my 11x14 filed camera.
> 
>  You can see the picture at
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1351565960
> 
> Is this likely to cover 20x24?  Any thoughts about that lens?

The Artar is a lens of the Dialyte type, a symmetrical design with four
air-spaced elements.  The original Dialyte was designed in 1899 and was renamed
Celor in 1904.  In 1904 the lens was redesigned using better glasses, resulting
in the Artar.   This is all from pp. 100-102 of A History of the Photographic
Lens by Rudolf Kingslake.

Modern versions of this lens are the Apo-Artar, Apo-Nikkor and Apo-Ronar. 
These lenses are all rated to cover about 46 degrees.   This figure is a
characteristic of this design.   Some of really long focal lengths have slightly
smaller coverage, probably because the glass elements were made smaller that
simply scaling the design up.

The equation to calculate the diameter D of the circle of coverage when
focused at infinity is  D = 2 f tan (theta / 2), where f is the focal length of
the lens.   Here theta is probably very close to 46 degrees, so for f = 19
inches one obtains D = 16.1 inches.

The diagonal of 20X24 is 31 inches, so this lens will not work for landscape
photography with 20x24 film.  For making a lifesize image, 1:1, the coverage
doubles to 32 inches, and so for this application the lens would cover 20x24.
As process photography was the original application, old catalogs would likely
list 32 inches as the coverage.

The diagonal of 11x14 is 17.8 inches, so the lens probably won't fully cover.

I think selling a lens for the likely use of distance photography (vs closeups)
and citing the coverage for 1:1 imaging is misleading.    The seller may not
have understood that the coverage they cited was for 1:1 and so have made an
honest mistake.

--Michael