How do I modify the Data Frame Extents from an ArcObjects application

Discussion created by dp3lw on Jun 19, 2012
Latest reply on Oct 17, 2013 by dk10
We're upgrading to ArcGIS 10 and we are changing a number of our feature classes and databases.  To assist our 2500 users we have written a program that converts old layers to the new layers where possible keeping the symbology etc. 

I need a little help in accessing the data frames associated with a map and changing the maximum extent when users click on the zoom out to full extent icon.  Going through the object models can be quite a chore. 

Could someone tell me which objects I'll need to use? 

The program is written in c#.