In 1968, Leitz responded to the critics of the non-TTL meter of the original Leicaflex by introducing its successor the Leicaflex SL with a TTLmeter. "SL" stood for "Selective Light", the name chosen by Leitz for its implementation of TTL metering. This system metered a limited area represented by the viewfinder's central microprism spot. At a time when SLR systems were divided between those embracing TTL metering at full aperture (such as Nikon and Konica, and those with mounts which permitted only stop-down metering (such as Pentax and Canon), Leitz chose to implement full-aperture metering on the Leicaflex SL.
Leitz also addressed complaints about the original Leicaflex focusing screen in the SL focusing screen, which offered a ground-glass focusing screen with a central microprism spot. This more conventional configuration did not prevent it from being very bright and comfortable. In fact, the brightness of the SL viewfinder remains unsurpassed up to the present day.
The Leicaflex SL replaced the mirror lock-up function of the original Leicaflex with a depth of field preview. The principal effect was to obsolete the rangefinder-derived 21mm f/3.4 Schneider Super-Angulon lens which, due to the protrusion of the rear element into the camera body, was designed to work with the mirror locked up and in conjunction with an external viewfinder. This lens cannot be mounted on the SL or its followers without mirror lockup. The original Leicaflex Super-Angulon was replaced by the retrofocus type 21mm f/4 Super-Angulon, which can be used conventionally.