fovy question


I have the following problem. I want to change my fovy, but i don’t want my object to grow/shrink in size. Is there a way to compensate? The reason i want to do this, is to change the angle between the ribs of a cube.
Hope you can help me with this.

modelview * vertex = vertex’
projection * vertex’ = vertex’’
inverseprojecion2 * vertex’’ = vertex’’’
inversemodelview *vertex’’’ = vertex’’’’

and you keep vertex’’’’ in your datastructure.