 Mirrorless cameras feature a larger sensor and interchangeable lenses, like DSLRs, but sacrifice the SLR mirror mechanism and viewfinder to save size and cost, and hence only offer live preview.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.