USSR lens Helios 81M is a six-celled anastigmat with single-layer or multi-layer (MS) clarification based on the Biotar 2/53 lens (Carl Zeiss Jena). According to the optical scheme - planar. One of the most common lenses of the USSR Specifications: Format: 35mm mirror Type: Constant focal length (fixed) Focus: Manual Focus System: M42 Optical design: 6 elements in 4 groups Focal length: 58mm Aperture: f / 2.0 - f / 16 Petal Aperture: 8 Diameter of filter thread: 49mm Weight: 270g Length: 42mm Year of production: 1975 Product condition: Good condition. Lenses without scratches and fungus. There is a micro hairline inside. The mechanics are working properly.