The Kenko Uniplus 12 Extension Tube for Sony Alpha Cameras is an optics-free mechanical linkage which provides 12mm of space between any Sony Alpha camera and any lens made to fit Sony Alpha cameras.  The Uniplus 12 is for moderately-close macro work, giving a 1:4 image reproduction ratio with a 50mm lens.  This is the right choice if you'd like to photograph a 4x5" area of someone's face, for example.

All of your Sony Alpha camera's metering and exposure functions are retained, and though it is best to manually focus whenever working in the macro realm you can have the option of AF whenever there is sufficient light entering the optical path to properly activate the camera's focusing system.

Provides full communication between lens and camera

Autoexposure and TTL/flash metering functions are retained 100%

Can provide AF function when enough light is present

Provides a 1:4 maximum magnification with a 50mm lens