The Carl Zeiss Docter Wetzlar Optic Apo-Germinar 450mm f9 lens

Background:

The Lens Vade Mecum tells us that Docter Optics, who were better known in the United Kingdom

for binoculars, were bought back by Carl Zeiss in the 1990's.  Production of lenses ended in 1997

following the death of their founder, leaving the cult legacy of the array of Docter Wetzlar Optic

lenses to disperse without marketing in the large format field.  Of the range of Docter Wetzlar

Optic lenses, the Apo-Germinar lenses relied on the blue prints of  two designs: a 4 element

dialyte construction for focal lengths up to and including 450mm [f9.0 240mm, 300mm, 360mm,

450mm] and 6 glass design for the focal range from 600mm - 1000mm.  Both lens types were

single coated optics.

 Docter Wetzlar Optic 450mm Apo-Germinar F9.0 in Copal 3 shutter

This legendary lens, produced by Docter Optic in Wetzlar Germany, had a very short lifespan and was

not marketed beyond its home.  Much of the information here has been supplied courtesy of Arne Croell,

author of the seminal article on Docter Optics in Viewcamera Magazine (2003).  More information here.

Docter Wetzlar Optic supplied MTF curves for their range of refined lenses.  Of these, the 150mm - 450mm

focal lengths were constructed as dialyte elements with a single coating.   The 450mm f9.0 Apo-Germinar

is an exceptional lens, standing out notably for its relatively compact size and weight in a Copal 3 shutter

yet possessing an image coverage of 535mm, unrivalled by smaller compact 450mm lenses.  Of these,

the Fujinon C type 450mm has a reputation as the most compact 450mm lens ever made to cover the

whole plate format (and 8x10" format too).  However its Copal 1 shutter size limits the image circle in

comparison to the Docter Wetzlar Optic and maximum apertures of the C type run at f12.5 or f12.0 for

the T type of the same focal length.   Photographers preferring faster optics for portraiture work may find

this consideration relevant.   

Tessar vs Dialyte vs Plasmat?

    - Zeiss Docter Wetzlar Optic 450mm f9.0 Dialyte type

    - Nikon Nikkor 450mm M f9.0 Tessar type

    - Fujinon C 450mm f12.5 Assymetrical Dialyte type

    - Fujinon CMW 450mm f8.0 Plasmat Type

The compact size; fast aperture and image covering circles of the 450mm lenses can be resolved back

to the lens construction designs. Modern lens manufacturers offers both plasmat and tessar type lenses in

this focal length so it can seem a little anachronistic for Docter Wetzlar Optic to offer a dialyte construction.

Older manufacturers offered 19" variations on a double anastigmat design (e.g Dagor Series III lenses)

however not on a par with the high definition of the current modern lenses.   Nikon offer a true Tessar type

450mm focal length, whereas the Fujinon offering shares an assymetrical variation of the  dialyte

construction compared to the symmetrical dialyte construction of the Docter Wetzlar Optic.  The Nikon 

offers a relatively greater image circle, a consequence of both the Tessar design (which has relatively

greater coverage for a dialyte type for its focal length, like for like) and  its larger Copal 3 shutter which

does not restrain the angle of coverage.  Tthe Fujinon's assymetrical design offers optimisation for infinity,

holding an advantage at 285 grams ~ approximately half the weight of the Docter Wetzlar Optic or the

Nikkor ~ due to the compact structure of its Copal 1 shutter.  The trade off however is a relative limitation

of movements.

Whereas the dialyte construction in the larger Copal 3 shutters of the Docter Wetzlar Optic offers a

superlative image covering circle, the peculiar 'Trimmring' attachment for spacing the front elements

of the dialyte enables optimisation of the infinity field at extremes of image coverage.  This is an

intelligent design albeit idiosyncratic for large format lens users.  The advantages of the true dialyte

design of the Docter Wetzlar Optic, is the optimised image definition across the greater image circle in

comparison to either the Tessar type (Nikon) or assymetrical dialyte (Fujinon) whilst retaining its compact

size relative to a much larger, bulkier and heavier plasmat type such as the Fuji CMW 450mm f8.0 type

or the Nikon Tessar equivalent.   Image circles of the plasmat types run at 520mm and 440mm at f22 for

infinity for each lens respectively.  Therefore the sole advantage of these heavier plasmat type lenses

over the image circle of  535mm of the Docter Wetzlar Optic (quoted as 530mm in some literature) lies in

the fractionally and extremely modest faster aperture of f8.0 against the Docter Wetzlar Optic lens of f9.0,

yet whilst the plasmat type requires larger and more expensive filters (86mm for the Fujinon compared to

58mm of the Apo-Germinar) and weighs nearly twice as heavy as the Apo-Germinar 450mm lens. The

smaller compact Copal 1 type Fujinon may indeed have a relatively greater circle of illumination for its

design compared to a scaled up Tessar type whose definition is less acceptable in the margins of this circle.

Although this may seem disconcerting news for plasmat lens owners, the relatively small batch production

numbers of Docter Wetzlar Optic lenses renders it less common.

MTF Curves:

Characteristics:

As seen above, the main distinctions of the Apo-Germinar 450mm f9.0 lie in two areas: firstly, its unrivalled

covering power at infinity of 535mm at f22 for infinity.  At repro' distances, this image circle approximately

doubles.  Secondly, a spacer ring adapter is supplied with the lens for image correction beyond 1:5

reproduction to 1: infinity reproduction, ensuring peripheral field sharpness whilst employing movements. 

For this combination, the Apo-Germinar 450mm f9.0 offers a superlative architectural process lens with an

amazing palette for image coverage yet while it remains compact. 

Filter size:                                58mm front threaded [0.75x pitch]

Flare Control:                          Excellent due to design and single coating lens for its relatively huge image circle.

                                                  In practice, comparable to Tessar types such as the Nikkor M or Fujinon C types.

Shutter:                                    Copal 3 [1s- 1/125s + B/T]  Significantly larger than the Fujinon C and consequently

                                                  has a greater image circle not limited by the narrow Copal 1 shutter of the Fujinon C. 

Aperture:                                  10 bladed apertures run from f9.0 to an amazing near pinhole f180.

Summary:                                This is quite an extraordinary lens which is very distinctive for its characteristics, leading

                                                  the field incomparably.  The Apo-Germinar 450mm f9.0 represents the ideal whole plate

                                                  format lens for travelling light and covering all possible movements of the Chamonix field       

                                                  camera without concern over limitations associated with the angle of coverage. 

                                                  Unfortunately discontinued following a limited batch of manufactured lenses, it represents

                                                  one of the best options available in the 450mm focal length particularly for photographers

                                                  undertaking extensive movements (i.e. architectural work or where perspective control is

                                                  critical for imaging) with impressively high definition and contrast for process work and

                                                  general use.

Other Zeiss Docter Wetzlar Optic lenses:

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