A system comprising two camera lines and an extensive range of M42 screw-mount lenses, from ultra-wide angle to super telephoto and telephoto zooms. The J-series cameras had a mechanical shutter, and exposure metering was performed not through the lens, but using a special window exposure meter, which was either built into the camera or mounted additionally. Starting with the TL series, TTL exposure metering appeared, and most TL Electro models received an electronically controlled shutter. All cameras of the system performed stop down exposure metering. The Electro AX also added aperture priority automatic exposure metering.