The IMAQ Vision 6.0 Concepts Manual has good detailed information on a variety of topics including calibration. Chapter 3 has 18 pages of information on calibration and setting up your imaging system.
If you installed the Vision 6 help, it should be under your Start>>Programs>>National Instruments>>Vision>>Documentation, or you could go to ni.com/support and look in product manuals pull down to find the link:
http://digital.ni.com/manuals.nsf/caba5d53e9b015a186256793004eebb7/a84f8c4bb40374c5862569a700520cc0?OpenDocument
This is fior the Vision 5, but it looks like the concepts are the same.
Hope this helps,
Brad
