Carl Zeiss Jena Orthometar 35mm f/4.5

Carl Zeiss Jena Orthometar 35mm f/4.5

The Carl Zeiss Jena Orthometar 35mm f/4.5 is a pre-war Contax wide-angle introduced in 1937. Zeiss offered it as a less expensive alternative to the faster 35mm f/2.8 Biogon, but it has an independent six-element, four-group optical identity.

The symmetrical Orthometar construction places two cemented doublets at the outside and two single elements around the central diaphragm. The lens uses the external Contax bayonet, incorporates its own focusing helicoid and is rangefinder-coupled.

It focuses to approximately 0.9 metres and has a five-blade diaphragm operating from f/4.5 to f/22. The front accepts 40.5mm screw-in filters. Its rear optical assembly is considerably shorter than that of the pre-war Biogon, allowing it to mount safely on the later Contax IIa and IIIa.

A separate 35mm finder is required for framing. Zeiss paired the Orthometar with the same 35mm finder used for the Biogon.

Optical qualities

Rendering

Zeiss promoted the Orthometar for its flat field and comparatively even edge definition. The nearly symmetrical layout is inherently favourable for controlling geometric distortion, lateral chromatic aberration and several off-axis aberrations.

The lens is slower than the Biogon, but the moderate f/4.5 aperture reduces the demands placed on spherical-aberration correction. It offers generous depth of field and is particularly suitable for architecture, landscape and general documentary photography.

Most surviving examples are uncoated. Contrast can consequently be moderate and strong backlight may produce flare. A hood is advisable when stray light can reach the front element.

Performance statements derived from later Orthometar-type lenses should not be transferred numerically to this exact lens. They are useful only for explaining the design family’s general correction principles.

At maximum aperture

Maximum-aperture performance should be evaluated with a correctly calibrated camera. A coupled rangefinder measures distance through a mechanical cam and does not inspect the image plane directly. Small errors in the body, mount or lens can therefore shift the sharp plane. Subject movement and field curvature may also be mistaken for optical softness. A clean, properly assembled lens should be tested at several distances before conclusions are drawn.

The widest setting provides the greatest light transmission and the least depth of field available from the design. Contrast can be reduced by residual aberrations, internal reflections or aged coatings. Bright point sources may show glow or flare. These effects vary between examples and should not be presented as a fixed signature of every surviving lens.

Stopped down

Closing the diaphragm increases depth of field and generally improves consistency across the 35mm frame. Middle apertures are often the practical choice for documentary work, landscapes and architecture. The smallest aperture provides more depth but is not automatically the sharpest setting because diffraction gradually reduces fine contrast.

Aperture shape depends on blade count and mechanical condition. Oil, bent blades or an incorrectly assembled iris can change both operation and out-of-focus highlights. Published blade counts should remain tied to the exact barrel version rather than copied between mounts.

Handling and compatibility

Contax and Kiev rangefinder lenses use either the internal standard-lens bayonet or the external bayonet. These interfaces serve different mechanical purposes even though they belong to the same camera system. Similarity to Nikon S or another rangefinder mount does not guarantee correct registration, coupling or infinity focus. A suitable adapter must reproduce the required focusing mechanism and keep the rear assembly clear of internal camera parts.

History

Development and Launch

The Contax Orthometar appeared in 1937 as a moderately priced 35mm wide-angle. Although its barrel closely resembles that of the pre-war Biogon, the shorter rear assembly and 6/4 optical formula make it a separate lens family.

Production Evolution

Early lenses reused Biogon-style depth-of-field engraving that extended to f/2.8 even though the Orthometar itself opens only to f/4.5. Standard examples carry the Carl Zeiss Jena engraving.

A small early group is reported with the erroneous “C. Zeiss Jean” engraving. At least one unusually marked example with a minimum aperture of f/45 has also been documented.

Sources disagree about the precise end of manufacture. The lens remained available in period catalogues after its initial production batches, but catalogue availability does not establish when the last lenses were manufactured. Production Year To therefore remains Unknown.

Special Editions/Variants

The early engraving error, the Biogon-style depth-of-field scale and the reported f/45-marked lens are meaningful factory variations, but they do not justify separate LeicaLensList profiles.

Collector Notes

The Orthometar is sometimes mistaken for a Biogon because of its similar chrome focusing barrel. The much shorter rear projection and f/4.5 engraving provide the clearest distinction.

Its short rear section also separates it mechanically from the pre-war Biogon and removes the latter lens’s principal Contax IIa/IIIa compatibility problem.