a virtual microscope slide includes images of a specimen for a given level of optical magnification which are associated and stored in a data structure . the forming of the data structure having the multiple z - plane images preferably includes automatically focusing at a principal reference focal plane and capturing and digitizing an optically magnified reference z - image and then shifting the specimen relative to the lens system by a predetermined increment to capture and digitize another z - plane image . preferably , a multiple sequence of z - plane images above and below the reference image and captured and digitized . for ease of retrieval and use , each reference image has its associated z - plane images are formed in a stack that is sent over the internet , or intranet to a local computer storage for quick retrieval when a viewer wants to mimic a focusing up or down to better view a detail in an image . thus , the resultant images are retrieved and displayed such that a virtual focusing capability is available to the user . the images can be formed with overlapping fields of depth , adjacent fields of depth , or wholly separated fields of depth .