The Sony A99II SLT camera is a different type of DSLR as it has no moving mirror, the R part in DSLR, Single Lens Reflex. Instead it uses a translucent mirror to pass light to the autofocus system at the same time as allowing for a live view in both the viewfinder and the back of the camera body. Mine had gotten a smudge and dust that would not come off so I thought it was time to replace it.