The BetterLight Scan Back is a so-called line scanner. It uses a large trilinear array of photo sensors (line of Red, Green and Blue Sensors).  Each sensor samples each pixel in the original by being passed over the original via a motor and lead screw, thus capturing each pixel three times.

The Metis DCS achieves even higher file sizes  by moving its trilinear array over a third of the original, and then using an ultra precise motor to move it up an additional third for a second scan, and finally repeating the process for the last area.

The Sinar 54 uses an area array sensor, and moves the sensor's x and y, offsetting each sample scan by .5 pixels and dithering multiple scans together.

These digital backs coupled with large format cameras provide the best possible reproduction and represent the highest level of digital imaging. They also require the most knowledgeable users.  However, since 2002, driven by the economic need to use volunteers, work/study students, etc.,  AIA has developed techniques, software adaptations, and special documentation to help novices use these devices with great success and ease.