When the Praktica LLC was introduced, it was considered a camera with remarkable design; with the benefit of hindsight it was indeed a true landmark.
At the close of the 1960s, full-aperture TTL metering was not uncommon, even for cameras using the M42 mount. However, maximum aperture indexing and the simulation of selected aperture with the M42 mount made it necessary to have further modifications to the mount itself; with the experience gained from the Pentacon super, Pentacon was well aware of the pitfalls. To banish the problem, a novel system was devised: the simulation circuit was moved from the camera body to the lens, making the connection between the lens and camera purely electric. Three contact pins at the back of the lens mate with three contact tracks on the camera body; the use of tracks rather than points takes care of the possible discrepancies in the final stopping position of the lens.
To enable the LLC to meter at full-aperture, electric versions of Meyer/Pentacon and Zeiss lenses were produced, and as an extra benefit, accessories were produced to allow for full-aperture metering and automatic diaphragm operation even when the lens is detached from the camera body, such as when used reversed or at the end of a bellows unit. A small number of third-party lens makers also offerred compatible electric lenses as well. With non-electric lenses the simulation section of the metering system can be shut down to effect stopped-down metering.
The LLC requires a 4.5V PX21 alkaline cell to run its meter, which can be a little difficult to find nowadays. Various methods of improvisation have been devised to use more readily-available batteries to effect the same functionality.
With the increased communication between camera and lens nowadays, other manufacturers had to follow the lead set by the Praktica LLC to employ electric connections.
TTL metering with electrical diaphragm control. This reflex camera offers the great advantage of keeping the finder image at the brightest even during light metering. This method of light metering at open aperture is made possible by the electric transmission of the diaphragm values. It can be utilized with lenses from 29 mm to 135 mm and also with appropriate accessories for taking close-ups. For all other PRAKTICA lenses without electric diaphragm control, light is metered with working aperture. By the internal light metering device, being part of the automatic diaphragm control, automatically the image angle of the lens used and the prolongation factors owing to accessories are taken into consideration.