Every camera manufacturer has its own brand of image stabilisation system. Most use mechanisms inside the lens, where gyroscopic sensors detect any camera movement and drive motors that shift an internal lens element to correct it. The trouble is, according to Sony, that these only counteract certain types of movement, namely pitch and yaw.
This is where you inadvertently twist the camera sideways or in an up-down direction as you take the picture. The movements may be so tiny you don't notice, but they can be enough to blur the fine detail in your pictures. This is typical of shots taken with telephoto lenses – actually, it affects all lenses, but telephotos magnify the blur and make it more obvious.
But these aren't the only movements that can cause blur. High-magnification images, particularly macro shots, are often spoiled by lateral and vertical movements, or x/y shifts, during the exposure. Sony's image stabiliser can correct these too.
The fifth axis of correction is 'roll', which is an unintended circular movement that's most obvious in video footage but can affect still images too, especially with slower handheld exposures at night, for example. You'll see it when a horizon that should have been straight is actually slightly skewed.
Sony says this is the world's first full frame camera with 5-axis image stabilisation. Olympus also has a 5-axis image-stabilisation system, first introduced with the OM-D E-M5, but this controls a smaller Micro Four Thirds sensor, and although there are commercial connections between the companies, Sony says the stabilisation technology in the a7 II is completely unconnected with Olympus's.
Some Sony lenses already have stabilisation built in, but here's where the system gets clever. The A7 II will use the axes of correction provided by the lens and supplement them with the extra axes available in the camera. You won't get 'double' stabilisation, but you will get the best blend of both systems.
The big advantage, of course, is that you can now get stabilised images with non-stabilised lenses, and that includes older Sony A-Mount lenses for its D-SLR and SLT cameras, which can be attached to the A7 II via an adaptor.
Sony is claiming the equivalent of 4.5 stops of correction from the new system, and we look forward to putting this to the test.
In the meantime, take a look at this Sony A7 II demo video.