Digital cameras come in a multitude of different types and sizes, and some of the jargon can be quite unhelpful. For example, ‘compact’ cameras aren’t necessarily compact and the real difference is that they have non-removable lenses. DSLRs and CSCs are both examples of interchangeable lens cameras, or ILCs, and these are differentiated by their design, sensor size and intended market. Most novices start off with a compact camera, move up to a DSLR or CSC when they become enthusiasts and then upgrade to a full-frame or medium format camera if they turn professional.
‘Alpha’ is the generic brand name used by Sony for its interchangeable lens cameras. This can be confusing because Sony makes cameras in two types – SLT (single lens translucent) and mirrorless models. Both are Alphas, but the Alpha A9 (mirrorless) and Alpha A99 II (SLT) are entirely different cameras with different lens mounts and lens ranges. Sony’s SLTs use Alpha A-mount lenses, while the mirrorless models use E-mount lenses.
SLT cameras are made by Sony as a kind of hybrid of the regular digital SLR design and the always-on live view of a mirrorless camera. They do have a mirror in the body, but it doesn’t flip up and down when you fire the shutter. Instead, it has a translucent surface so that the image can pass straight through to the sensor on the back of the camera.
The point of this design is that the fixed mirror can reflect light back on to the camera’s fast phase-detection autofocus sensor even while the image is being composed using a live view image on the rear screen or in the electronic viewfinder.
The downside is that you get all the bulk of a DSLR without the clarity of an optical viewfinder. Sony still makes its SLT models but with improvements in sensor-based hybrid autofocus technology, most expect it will soon transfer all its efforts to its mirrorless models.