Does the Zeiss software have some form of image compression going on?

The images are not stored as RAW data; instead, they are losslessly compressed. Achieving a compression factor of 2 with this method is quite common. In theory, even higher compression could be possible, but CMOS cameras tend to produce more noise compared to older CCD cameras, and noise cannot be compressed effectively.

The size after compression depends on the input image, which explains the variations. For example, if an image is completely overexposed or entirely black, the compressed images should be very small because it only needs to store the information that all pixels have a grayscale value of 255 or 0.