SOM Berthiot Flor 50mm f/1.5

SOM Berthiot Flor 50mm f/1.5

The SOM Berthiot Flor 50mm f/1.5 is a French high-speed standard lens documented in an original rangefinder-coupled Leica M39 mount. Leitz Auction dates the known configuration broadly to the 1940s and describes a heavy brass barrel with a polished chrome finish and early coated optics. Its 50mm focal length and f/1.5 aperture identify a distinct Flor made for Leica-thread rangefinder use.

The exact optical formula, diaphragm blade count, filter fitting and minimum focusing distance have not been established from reliable documentation. Those fields remain unknown. This profile does not borrow specifications from slower Flor lenses, cine optics, the separate 55mm f/1.5 Flor or other SOM Berthiot products.

Optical qualities

Rendering

No verified factory optical section or controlled test for the exact coupled 50mm f/1.5 has been located. The Flor name was applied to more than one focal length and aperture, so it cannot be used by itself to infer an element count or formula. Evidence for this entry is strongest for the physical barrel, period, coating and camera compatibility.

At 50mm, the lens gives a standard field of view on 35mm film. The f/1.5 aperture supports selective focus and lower-light photography. Descriptions such as glow, swirl or painterly bokeh are not treated as specifications. The appearance of a photograph depends on aperture, focus distance, background, film or sensor and the condition of the optical surfaces.

At f/1.5

Full aperture produces the shallowest depth of field and makes rangefinder accuracy important. The lens cam should be checked at infinity and at several measured distances. A focus error can result from body calibration, cam wear, helicoid servicing or incorrect assembly.

The documented early coating may improve transmission and flare behaviour relative to an uncoated optical unit, but no quantitative measurement for the exact Flor has been found. Coating wear, haze, separation, fungus and internal contamination can lower contrast substantially. Such effects describe condition, not an intended signature of the model.

Stopped down

Closing the diaphragm increases depth of field and generally improves consistency beyond the central field. The exact blade count, smallest marked setting and shape of the opening must be confirmed from an original lens. They should not be copied from a related Berthiot optic merely because the family name is the same.

Handling and compatibility

The heavy brass construction places more load on a screw-mount camera than a small collapsible standard lens, so the assembly should be supported during mounting and removal. Its original coupling cam is intended to operate a Leica-standard rangefinder. Correct thread pitch alone does not prove correct register or coupling.

An LTM-to-M adapter allows use on many Leica M bodies, while a mirrorless adapter provides direct sensor focus. Neither makes an inaccurate historical cam correct. A 50mm viewfinder is available in many compatible bodies, but earlier cameras may require an external finder. Until the front fitting is documented, filters and hoods should be selected by direct measurement.

History

Development and Launch

The Berthiot optical business traces its origins to Claude Berthiot's Paris workshop, founded in 1857. Historical accounts record later Lacour-Berthiot naming and the use of SOM, Société d'Optique et de Mécanique de Haute Précision, during the twentieth century. The company produced photographic, cinema and instrument optics in France.

Leitz Auction assigns the coupled Flor 1.5/50mm to the 1940s. Its original M39 focusing mount, heavy polished brass construction and early coating place it within SOM Berthiot's small-format photographic work of that decade. A precise launch year and original catalogue reference have not been located, so the broader period is retained.

Production Evolution

The available exact-version record documents a polished chrome brass barrel and coated optics. It does not establish when coating began, whether uncoated Leica-thread examples were sold, or whether the diaphragm and engraving changed during production. No sequence is invented from isolated auction photographs.

The 55mm f/1.5 Flor in an A. Garneau-coupled mount is catalogued separately. Its focal length and documented mechanical attribution make it more than a cosmetic variation. Likewise, cine and projection Flor lenses require their own evidence and are not included here.

Special Editions/Variants

No factory commemorative edition or separately named special version of the 50mm f/1.5 Leica-thread Flor has been reliably documented. Auction suggestions about individual examples or tiny batches are not converted into a production total. A later workshop conversion should be described as a conversion rather than a factory variant.

Collector Notes

Confirm the SOM Berthiot and Flor engravings, 1:1.5 50mm specification, polished heavy-brass barrel, Leica-standard M39 mount and functional coupling cam. Compare the mount architecture with a documented original, since a converted optical head may carry correct front engraving but different rear mechanics.

Check rangefinder agreement, helicoid smoothness, aperture operation and infinity position. Inspect the early coated glass for haze, fungus, separation, coating wear and cleaning damage. Do not generalise the condition, serial number, accessories, provenance or sale price of one auction example to the model.