M42
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Optical
Bertele Sonnar formula reducing air/glass interfaces to six by adding low-index glass; classic 5cm f2 was 6 elements in 3 groups and f1.5 was 7 elements in 3 groups.
Updated
Jul 10, 2026
The Sonnar name traces to Ludwig Bertele, who worked for Ernemann (Krupp-Ernemann Kinoapparate AG) and developed the Ernostar F2, a 5-element/4-group asymmetric design with eight air/glass interfaces. After Ernemann merged with Zeiss, Bertele filled the space between the 2nd and 3rd element with low-index glass, reducing the design to just 6 air/glass interfaces and improving light transmission by nearly 10%. This gave rise to the classic Sonnar formula. The 5cm f2 Sonnar of 1931 was 6 elements in 3 groups (1-3-2), and by splitting the rear doublet into a triplet the 5cm f1.5 Sonnar of 1932 was born, with 7 elements in 3 groups (1-3-3). The whole design philosophy of Zeiss differed sharply from Leitz: where Leitz pursued highly corrected, symmetric double-Gauss designs (Summar, Xenon, Summitar) prioritizing distortion correction and resolution, Zeiss prioritized a bright, high-contrast image, treating flatness of field and geometric distortion as secondary to light transmission. The minimized air/glass count was a direct response to the primitive coatings of the era. The design was revived by Zeiss in the mid-2000s as the C-Sonnar T* 50mm f1.5 in the ZM (Leica M) series with modern coatings and only minor optical changes, keeping the classic formula alive. The C-Sonnar has a genuine cult following: reviewers note that Sonnar designs have a 'very particular rendering' prized by many photographers, especially for portraiture and its distinctive bokeh, though skeptics argue it is an old formula sold on nostalgia. Note: the reviews describe the M-mount ZM C-Sonnar and prewar Zeiss Jena 5cm Sonnars; specifics for an M42-mount 'Carl Zeiss Sonnar' are not directly covered, so many mechanical fields below are marked unknown.
Verdict: A Carl Zeiss Sonnar is for the photographer who values character over clinical perfection — a bright, high-contrast, portrait-flattering rendering with prized bokeh, born from Bertele's classic low-surface-count design. The fast f1.5 versions demand that you master their pronounced focus shift, while slower Sonnars like the 85mm f2.8 reward you with lovely circular bokeh and a fully usable wide-open aperture. Choose it for its cult rendering and history, not for corner-to-corner test-chart performance.
A signature Sonnar strength, cult-followed and often described as lovely, circular and smooth with no swirl or bubble effects.
Fast Sonnars suffer pronounced focus shift that complicates critical sharpness, with quality dropping off at close focus, though wide-open remains usable.
High contrast by design, with a usable wide-open aperture not veiled by haze or low contrast.
Real adapters from our shop that fit this lens mount.
Standard · ฿325 · In stock
Standard · ฿325 · In stock
Standard · ฿325 · In stock
Standard · ฿325 · In stock
Standard · ฿540 · In stock
Standard · ฿540 · In stock
Standard · ฿540 · In stock
Standard · ฿540 · In stock
Standard · ฿540 · In stock
Standard · ฿1,250 · In stock
Standard · ฿890 · Out of stock
Standard · ฿890 · Out of stock
The Sonnar name traces to Ludwig Bertele, who worked for Ernemann (Krupp-Ernemann Kinoapparate AG) and developed the Ernostar F2, a 5-element/4-group asymmetric design with eight air/glass interfaces. After Ernemann merged with Zeiss, Bertele filled the space between the 2nd and 3rd element with low-index glass, reducing the design to just 6 air/glass interfaces and improving light transmission by nearly 10%. This gave rise to the classic Sonnar formula. The 5cm f2 Sonnar of 1931 was 6 elements in 3 groups (1-3-2), and by splitting the rear doublet into a triplet the 5cm f1.5 Sonnar of 1932 was born, with 7 elements in 3 groups (1-3-3). The whole design philosophy of Zeiss differed sharply from Leitz: where Leitz pursued highly corrected, symmetric double-Gauss designs (Summar, Xenon, Summitar) prioritizing distortion correction and resolution, Zeiss prioritized a bright, high-contrast image, treating flatness of field and geometric distortion as secondary to light transmission. The minimized air/glass count was a direct response to the primitive coatings of the era. The design was revived by Zeiss in the mid-2000s as the C-Sonnar T* 50mm f1.5 in the ZM (Leica M) series with modern coatings and only minor optical changes, keeping the classic formula alive. The C-Sonnar has a genuine cult following: reviewers note that Sonnar designs have a 'very particular rendering' prized by many photographers, especially for portraiture and its distinctive bokeh, though skeptics argue it is an old formula sold on nostalgia. Note: the reviews describe the M-mount ZM C-Sonnar and prewar Zeiss Jena 5cm Sonnars; specifics for an M42-mount 'Carl Zeiss Sonnar' are not directly covered, so many mechanical fields below are marked unknown.