Interchangeable lens 35mm rangefinder cameras made their debut over 90 years ago when Leitz introduced the Leica II and Zeiss debuted the Contax I. The first lenses for these cameras were Tessar formula lenses of modest speed. The 5cm F3.5 Tessar was produced in Contax RF mount in 1931, and was soon followed by the 5cm F2.8 Tessar a few months later. The 5cm F2.8 Tessar was a poor performer used wide-open, too far of a stretch of the 4 element in 3 groups, 1-1-2 design for the available glass of the day. The Leica II was introduced with the Elmar 50mm F3.5, also a Tessar type 1-1-2 design. The Elmar has the aperture behind the front element rather than the middle element as it is on the Zeiss Tessar. Leitz soon introduced the 50mm F2.5 Hektor, a 6 element in 3 groups, 2-2-2 formula lens. This lens is also soft used wide-open. The race for speed was on.
Ludwig Bertele’s Sonnar is a break-through formula that embodies fast optics in a compact design. 2021 is the 90th birthday of Bertele’s 5cm F2 Sonnar. This lens is the first Sonnar to be introduced for the new Contax camera. 2022 is the 90th birthday for the 5cm F1.5 Sonnar.
2022 was a good year for me, two very special Sonnars came my way. The first- Ninety years after it was manufactured, a Carl Zeiss Jena 5cm F1.5 Sonnar from the first batch of 100 lenses completed, October 1932. This can be considered the trial batch, the optical formula and design of the lens was changed soon after. The second very special Sonnar is the Skyllaney pre-production 5cm F2 Bertele Sonnar.
Zeiss and Leitz brought out full lines of interchangeable lenses for their cameras, and dominated the market for 35mm format. The design philosophies of the two companies were very different.
Leitz designers believed that lenses should be highly corrected with small amounts of residual aberration. Their designs made use of double-Gauss optics, lenses with highly symmetric designs. Pairs of similar image-forming optics, placed back-to-back, will cancel out aberrations. Think of two prisms placed back-to-back: the first splits white light into a rainbow, the second prism combines the rainbow back to white light. The optical pairs are “highly symmetric”, not “completely symmetric”. In the 1920s it was found that introducing a small amount of asymmetry into the symmetric Planar formula lens allowed for much wider apertures. The Summar 5cm F2, Xenon 5cm F1.5, and Summitar 5cm F2 of the 1930s were well-corrected for distortion, highly color-corrected, and had a reputation for fine resolution. The Xenon is a 7 element in 5 group optic, with 10 air/glass interfaces. These lenses were not coated, and each air/glass interface reflected 4% of the light coming through it. The result is lower contrast and almost 1 F-Stop loss in transmission. All of these lenses used soft glass for the front element, making it very difficult to find one in good condition. If you do, the Bloom on the glass acts as a natural lens coating. Bloom is oxidation of the glass, which changes the refractive index of the surface. This reduces reflections. Good copies today perform better than when they were new.
Ludwig Bertele placed more importance on producing a bright image with high contrast. His designs minimized the number of air/glass interfaces using groups of cemented elements in asymmetric designs. Ludwig Bertele worked for Ernemann (Krupp-ErnemannKinoapparate AG) and developed the “Ernostar” F2. This lens had 5 elements in 4 groups, an asymmetric 1-1-1-2 configuration, eight air/glass interfaces. Ernemann merged with Zeiss, and Bertele created their most famous lens of the 1930s by filling in the space between the 2nd and 3rd element of the Ernostar with low index of refraction glass. This improved transmission by almost 10%. Corrections for flatness of field and geometric distortion were secondary to transmission of light.
Ludwig Bertele’s Sonnar is a break-through formula that embodies fast optics in a compact design. 2021 is the 90th birthday of Bertele’s 5cm F2 Sonnar. This lens is the first Sonnar to be introduced for the new Contax camera. 2022 is the 90th birthday for the 5cm F1.5 Sonnar.
2022 was a good year for me, two very special Sonnars came my way. The first- Ninety years after it was manufactured, a Carl Zeiss Jena 5cm F1.5 Sonnar from the first batch of 100 lenses completed, October 1932. This can be considered the trial batch, the optical formula and design of the lens was changed soon after. The second very special Sonnar is the Skyllaney pre-production 5cm F2 Bertele Sonnar.
Zeiss and Leitz brought out full lines of interchangeable lenses for their cameras, and dominated the market for 35mm format. The design philosophies of the two companies were very different.
Leitz designers believed that lenses should be highly corrected with small amounts of residual aberration. Their designs made use of double-Gauss optics, lenses with highly symmetric designs. Pairs of similar image-forming optics, placed back-to-back, will cancel out aberrations. Think of two prisms placed back-to-back: the first splits white light into a rainbow, the second prism combines the rainbow back to white light. The optical pairs are “highly symmetric”, not “completely symmetric”. In the 1920s it was found that introducing a small amount of asymmetry into the symmetric Planar formula lens allowed for much wider apertures. The Summar 5cm F2, Xenon 5cm F1.5, and Summitar 5cm F2 of the 1930s were well-corrected for distortion, highly color-corrected, and had a reputation for fine resolution. The Xenon is a 7 element in 5 group optic, with 10 air/glass interfaces. These lenses were not coated, and each air/glass interface reflected 4% of the light coming through it. The result is lower contrast and almost 1 F-Stop loss in transmission. All of these lenses used soft glass for the front element, making it very difficult to find one in good condition. If you do, the Bloom on the glass acts as a natural lens coating. Bloom is oxidation of the glass, which changes the refractive index of the surface. This reduces reflections. Good copies today perform better than when they were new.
Ludwig Bertele placed more importance on producing a bright image with high contrast. His designs minimized the number of air/glass interfaces using groups of cemented elements in asymmetric designs. Ludwig Bertele worked for Ernemann (Krupp-ErnemannKinoapparate AG) and developed the “Ernostar” F2. This lens had 5 elements in 4 groups, an asymmetric 1-1-1-2 configuration, eight air/glass interfaces. Ernemann merged with Zeiss, and Bertele created their most famous lens of the 1930s by filling in the space between the 2nd and 3rd element of the Ernostar with low index of refraction glass. This improved transmission by almost 10%. Corrections for flatness of field and geometric distortion were secondary to transmission of light.
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