This is a fantastic Carl Zeiss Jena DDR 135mm f3.5 MC S Sonnar M42 lens. It is a prime lens that is compatible with M42 mount. The lens is in great shape and comes with a skylight filter. The Carl Zeiss Jena lens is perfect for SLR cameras and has a maximum aperture of f/3.5. It focuses manually and has a fixed focal length of 135mm. This lens is great for photography enthusiasts and professionals alike. Nice lens, quality feel, substantial materials and proper glass. Threaded fitting but I believe that an adapter could allow this to fit a micro four thirds and that would be great to use.
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