I’ve been wrestling with a database problem for a couple of days and I’m stumped.  I wonder if any of you might be able to help?  I’m dealing with several hundred tables that include records for wildlife sites  For each record, there is a field that includes the site identifier appended to the path in my computer and a .tif suffix, like these examples: 
E:\Work\OWI\LIDAR\Owl_Landscapes\p99\p99sliced\rnd_SI_PK_UR3.tif 
E:\Work\OWI\LIDAR\Owl_Landscapes\p99\p99sliced\rnd_SI_PK_20100195.tif 
[Site identifier in bold italics] 
I need to create a new field in each table that holds only the site identifier, minus the path and .tif suffix.  I’m somewhat familiar with substring and Munger formulas that I have used to extract parts of strings.  But in this case, some site identifiers have mixed text/numeric characters and the string length is different among different records, so I can’t get these formulas to work.  Can someone offer advice?
Dave