Softimage Xsi: Matching cameras

Heya,


I've been looking for a method to match camera lenses with the Softimage camera. All this while, I've been doing it by calculating the field of view which is tedious and inaccurate most times. But it was always ok as it was pre-viz that it was used for.


This time round, I need to do it on the shoot itself and was kinda hoping for a quick way of actually changing the lenses if the director wanted to do that on set.


I've heard about a formula to translate the data but have not found any. Any ideas? This is a 35mm film camera. I'm using Soft3.9/4.0.


Any help would be VERY much appreciated. ;P


Thanks!