Ola Ken,
The real lens always have distortions, Wide lens for example, which 3d applications cant replicate, a few ones can, but its a real slow render.
The workflow secret to all Films and Tv productions is get your shot (need to take note of lens and Camera type, Digital Cameras have some values to be converted to match real film lenses) and bring this data for example in a 3d tracking software, un-distort the shot, track it, it which will generate a 3d lens to you, import in EIAS, render your 3d scene, bring the EIAS Render to your compose software like After Effects, and distort the EIAS render to match the real scene, appears tricky, but when you get the workflow, everything becomes perfect.
Take a look on this Syntheyes VIdeo Tutorials:
http://www.ssontech.com/content/lens1flow.htm
http://www.ssontech.com/content/lens2flow.htm
http://www.ssontech.com/content/centering.htm
http://www.ssontech.com/content/lensalg.htm
http://www.ssontech.com/content/lensflo.htm
http://www.ssontech.com/content/lensGrid.pdf
Hope this help
Thanks
Tom