The SLT, developed by Sony, uses a mirror similar to that found in a DSLR. However, unlike the moving and fully reflective mirror of DSLRs, the SLT mirror is fixed and semi-reflective. New Zealand-based British photographer Gordon Laing describes the technology:" fixed semi-reflective mirror allows around 70% of the light to pass through to the sensor for full-time live view composition, but reflects the remaining 30% or so to the phase change AF system, allowing quick and continuous autofocusing in Live View and movie modes. 30% is however too little for a traditional optical viewfinder, so Sony doesn't bother, instead using the main sensor to deliver a live image to an electronic viewfinder in addition to the main rear screen for composition."